Association of Modest Preoperative Weight Loss and 30-Day Outcomes After Bariatric Surgery: A Contemporary MBSAQIP Analysis

Association of Modest Preoperative Weight Loss and 30-Day Outcomes After Bariatric Surgery: A Contemporary MBSAQIP Analysis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Association of Modest Preoperative Weight Loss and 30-Day Outcomes After Bariatric Surgery: A Contemporary MBSAQIP Analysis Amir Monshizadeh, Masoud Rezvani, Mohammad Talebpour, Seyed Hossein Hosseini Nourzad, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8863406/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background Preoperative weight loss is commonly encouraged before bariatric surgery, yet its impact on short-term postoperative outcomes in contemporary practice remains uncertain. We evaluated the association between preoperative weight loss and 30-day postoperative outcomes using recent national registry data. Methods We conducted a retrospective cohort study using the 2020–2023 Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) Participant Use File. Patients with body mass index ≥ 35 kg/m² undergoing minimally invasive sleeve gastrectomy or Roux-en-Y gastric bypass were included. Preoperative weight loss was defined as a ≥ 2.0 kg reduction comparing the highest recorded weight within one year before surgery to the weight closest to the operative date, reflecting meaningful change beyond routine registry measurement variability. The primary outcome was 30-day serious postoperative complications, defined using the MBSAQIP bariatric surgical risk/benefit calculator composite. Multivariable logistic regression with robust standard errors was used. Prespecified sensitivity analyses included procedure-specific models, exclusion of robotic-assisted cases, and complete-case analysis for venous thromboembolism prophylaxis. Results Among 621,849 patients, 68.2% experienced preoperative weight loss. Preoperative weight loss was associated with lower adjusted odds of serious postoperative complications (adjusted OR 0.96, 95% CI 0.92–0.99). Weight loss was also associated with reduced venous thromboembolism (OR 0.88, 95% CI 0.78–0.98) and shorter postoperative length of stay (negative binomial incidence rate ratio 0.98, 95% CI 0.98–0.99). Findings were consistent across sensitivity analyses. Conclusions In a large contemporary national cohort, preoperative weight loss was associated with a statistically significant but modest reduction in serious postoperative complications and venous thromboembolism after bariatric surgery. These findings suggest that preoperative weight loss is associated with a modest incremental reduction in short-term postoperative risk but should not be used as the sole universal requirement for access to surgery. Trial registration Not applicable. Bariatric surgery Preoperative weight loss MBSAQIP Serious complications Venous thromboembolism Sleeve gastrectomy Roux-en-Y gastric bypass Figures Figure 1 Figure 2 Background Obesity is a major global public health challenge, affecting more than 890 million adults worldwide and contributing substantially to preventable morbidity, mortality, and healthcare expenditures [ 1 – 3 ]. Metabolic and bariatric surgery remains the most effective and durable treatment for severe obesity, producing sustained weight loss and significant improvement in obesity-related comorbidities, including type 2 diabetes [ 4 , 5 ]. Despite these benefits, bariatric surgery carries inherent perioperative risks, underscoring the importance of identifying modifiable preoperative factors that may influence short-term postoperative outcomes. Preoperative weight loss is commonly encouraged—and in some settings required by insurers or clinical pathways—based on the premise that modest weight reduction may improve perioperative outcomes [ 6 – 9 ]. However, the value of preoperative weight loss for reducing short-term postoperative morbidity remains incompletely defined. Prior studies have reported heterogeneous associations, with effect estimates varying by procedure type, exposure definition, and outcome selection [ 10 – 13 ]. As a result, the clinical relevance of preoperative weight loss remains debated, and mandatory requirements persist despite inconsistent evidence. Large registry-based analyses using MBSAQIP have improved statistical power and outcome ascertainment, yet uncertainty persists regarding the magnitude and consistency of the association between preoperative weight loss and short-term postoperative outcomes in contemporary practice [ 10 – 14 ]. In parallel, smaller interventional studies of preoperative dietary regimens (e.g., very-low-calorie diets) suggest potential perioperative technical benefits, but do not fully resolve questions about short-term morbidity in contemporary registry-based practice [ 15 ]. Differences in exposure definitions and outcome selection—often emphasizing mortality or isolated complications rather than standardized morbidity composites—have limited comparability across studies and contributed to ongoing debate [ 6 , 12 , 13 ]. Accordingly, we performed a contemporary analysis of the MBSAQIP Participant Use File from 2020 to 2023 to evaluate the association between modest preoperative weight loss and 30-day postoperative outcomes following minimally invasive sleeve gastrectomy and Roux-en-Y gastric bypass. Our primary objective was to quantify the association between preoperative weight loss and serious postoperative complications, defined using the MBSAQIP bariatric surgical risk/benefit calculator composite [ 17 ], using a large national cohort from the MBSAQIP Participant Use File [ 16 ]. Methods Study Design and Data Source We conducted a retrospective cohort study using the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) Participant Use File (PUF) from 2020 to 2023. MBSAQIP is a national clinical registry that uses prospective, standardized data collection to capture perioperative variables and 30-day postoperative outcomes [ 16 ]. The dataset is fully de-identified; therefore, this study was exempt from institutional review board oversight. Cohort Selection and Preprocessing Patients undergoing minimally invasive sleeve gastrectomy or Roux-en-Y gastric bypass were identified using Current Procedural Terminology (CPT) codes 43775 and 43644, respectively. Patients with a preoperative body mass index < 35 kg/m² were excluded. To restrict the cohort to elective primary bariatric procedures and ensure consistent attribution of postoperative outcomes, we excluded non–minimally invasive approaches, revision or conversion operations, cases with incomplete 30-day follow-up, American Society of Anesthesiologists (ASA) physical status class V, and patients with a preoperative hospital length of stay greater than zero days. Additional exclusions were applied to minimize confounding from acute illness or perioperative instability, including preoperative infection, sepsis or septic shock, pneumonia, ventilator dependence, confirmed or suspected preoperative COVID-19 infection, and missing postoperative length of stay. Patients with missing ASA class were excluded given its central role in risk adjustment. Age was restricted to 13–80 years because MBSAQIP top- and bottom-codes ages outside this range for de-identification, limiting interpretability of age as a continuous covariate in risk-adjusted models [ 16 ]. Cases with unknown sex designation were excluded during initial data quality checks to harmonize variable coding. Exposure Definition The primary exposure was preoperative weight change, derived from registry-recorded anthropometric measurements. Weight change was calculated as the difference between the weight recorded closest to the operative date and the highest weight recorded within one year prior to surgery, as specified in the MBSAQIP Participant Use File [ 16 , 18 ]. For all primary analyses, a prespecified categorical exposure variable was used, classifying patients as having preoperative weight loss (≥ 2.0 kg reduction) or no meaningful preoperative weight change (− 2.0 to + 2.0 kg). The 2.0 kg threshold was selected a priori to exceed routine scale-related and day-to-day weight fluctuation and to distinguish modest, clinically relevant weight reduction from measurement noise in registry data. Because the MBSAQIP variable anchors weight change to the highest recorded weight within the preceding year, meaningful preoperative weight gain could not be consistently distinguished in this dataset. Therefore, analyses focused on the comparison between modest preoperative weight loss and weight stability. Covariates Prespecified preoperative covariates included age, sex, race, Hispanic ethnicity, American Society of Anesthesiologists (ASA) physical status (I–II, III, or IV), hypertension, chronic obstructive pulmonary disease, obstructive sleep apnea, smoking status, diabetes mellitus, hyperlipidemia, renal insufficiency, dialysis dependence, gastroesophageal reflux disease, prior pulmonary embolism, immunosuppression, and inferior vena cava filter use. Race was modeled as a three-category variable (White, Black or African American, and Other), with the “Other” category combining less frequent racial groups to ensure stable multivariable estimates. Two composite variables were constructed in accordance with the MBSAQIP bariatric surgical risk/benefit calculator framework: cardiac history (history of myocardial infarction, percutaneous coronary intervention, or prior cardiac surgery) and vascular history (history of venous stasis, venous thromboembolism requiring therapy, or therapeutic anticoagulation) [ 17 ]. Venous thromboembolism prophylaxis method was modeled as a three-level categorical variable (mechanical only, pharmacologic only, or combined mechanical and pharmacologic). Missing data were minimal and were primarily limited to prophylaxis method, which was retained as an explicit category in the primary analysis and evaluated using complete-case sensitivity analyses. Outcomes The primary outcome was serious postoperative complications within 30 days, defined identically to the MBSAQIP bariatric surgical risk/benefit calculator as the occurrence of one or more of the following: death; unplanned intensive care unit admission; reoperation; procedural intervention; organ-space infection; pneumonia; unplanned intubation; pulmonary embolism; ventilator dependence > 48 hours; progressive renal insufficiency; acute renal failure; stroke; cardiac arrest; myocardial infarction; transfusion; deep vein thrombosis; sepsis; or septic shock [ 17 ]. This composite outcome was selected a priori to enable standardized benchmarking against national MBSAQIP risk estimates. Secondary outcomes included mortality, venous thromboembolism, anastomotic or staple-line leak, 30-day readmission, reoperation, non-operative intervention, gastrointestinal bleeding, transfusion, surgical-site infection (superficial, deep, and organ space), and postoperative length of stay [ 16 ]. Statistical Analysis Binary outcomes were analyzed using multivariable logistic regression and are reported as adjusted odds ratios (ORs) with 95% confidence intervals. Postoperative length of stay was analyzed using negative binomial regression and is reported as an incidence rate ratio (IRR) with 95% confidence intervals to account for right skewed and over dispersed count data. Robust standard errors were used for all models. The exposure was modeled as a binary comparison of preoperative weight loss versus no meaningful preoperative weight change, with only one exposure representation included per model. All prespecified covariates were entered simultaneously. Statistical significance was defined as a two-sided p-value < 0.05. To enhance clinical interpretability, marginal standardized risks were derived from the primary model to estimate adjusted absolute risk differences and numbers needed to treat. Prespecified supportive analyses included BMI-stratified models (< 50 vs ≥ 50 kg/m²) with formal interaction testing and E-value analysis to assess robustness to unmeasured confounding. These analyses did not alter the primary exposure or outcome definitions. Supportive dose–response analyses modeled continuous preoperative weight change using restricted cubic splines. Sensitivity Analyses Prespecified sensitivity analyses were performed to assess the robustness of the association between preoperative weight loss and serious postoperative complications. These included stratified analyses by procedure type (sleeve gastrectomy versus Roux-en-Y gastric bypass), exclusion of robotic-assisted cases, and a complete-case sensitivity analysis excluding patients with missing values for venous thromboembolism prophylaxis method. In the primary analysis, missing values for venous thromboembolism prophylaxis method were retained as an explicit category. All sensitivity analyses used identical model specifications and covariate adjustment as the primary analysis. Software Analyses were performed using Python (version 3.12.12), including pandas (version 2.2.2) and statsmodels (version 0.14.6). Results Study Cohort The MBSAQIP Participant Use File from 2020–2023 initially included 828,481 cases. After application of prespecified exclusion criteria and data cleaning, a total of 621,849 patients constituted the final analytic cohort. Of these, 451,227 (72.6%) underwent minimally invasive sleeve gastrectomy (CPT 43775), and 170,622 (27.4%) underwent minimally invasive Roux-en-Y gastric bypass (CPT 43644). Baseline demographic characteristics, comorbidities, perioperative features, and postoperative outcomes for the overall cohort are summarized in Table 1 . Preoperative weight loss was common, with 423,962 patients (68.2%) classified as having experienced preoperative weight loss and 197,887 (31.8%) classified as having no meaningful preoperative weight change. Among patients with preoperative weight loss, the mean weight change was − 7.8 ± 5.8 kg, reflecting heterogeneity in the magnitude of weight loss. Table 1 Baseline characteristics, operative details, and 30-day outcomes of patients undergoing primary minimally invasive bariatric surgery with BMI ≥ 35 kg/m² (N = 621,849). Variable Value (Mean ± SD or N [%]) Demographics Age (years) 43.0 ± 11.7 Body mass index (kg/m²) 45.6 ± 7.4 Female sex 510,438 (82.1) Race White 398,572 (64.1) Black / African American 127,525 (20.5) Other¹ 95,752 (15.4) Hispanic ethnicity 109,345 (17.6) Functional status Functionally independent 618,282 (99.43) Not independent (partial, total, or missing) 3,567 (0.57) ASA class² ASA I–II 108,164 (17.4) ASA III 492,279 (79.2) ASA IV 21,406 (3.4) VTE prophylaxis method Mechanical and pharmacologic 552,929 (88.9%) Mechanical only 41,503 (6.7%) Pharmacologic only 8,806 (1.4%) Missing 18,611 (3.0%) Preoperative weight change Preoperative weight loss 423,962 (68.2) No meaningful weight change 197,887 (31.8) Weight change (kg) −7.8 ± 5.8 Comorbidities Diabetes mellitus 143,022 (23.0) Hypertension 271,976 (43.7) Sleep apnea 234,046 (37.6) Gastroesophageal reflux disease 184,684 (29.7) Chronic obstructive pulmonary disease 7,022 (1.1) Renal insufficiency 3,214 (0.5) Hyperlipidemia 138,793 (22.3) Immunosuppression 14,031 (2.3) Smoker 40,121 (6.5) Inferior vena cava filter 1,194 (0.2) On dialysis 1,905 (0.3) Cardiac history 13,253 (2.1) Vascular history 26,692 (4.3) History of pulmonary embolism 8,535 (1.4) Surgical and intraoperative information Minimally invasive sleeve gastrectomy 451,227 (72.6) Minimally invasive Roux-en-Y gastric bypass 170,622 (27.4) Robotic assistance 172,746 (27.8) 30-day outcomes Serious complications³ 13,162 (2.1) Mortality 426 (0.1) 30-day readmission 17,884 (2.9) 30-day reoperation 5,452 (0.9) 30-day reintervention 4,211 (0.7) Transfusion 3,797 (0.61) Gastrointestinal bleeding 2,349 (0.38) Venous thromboembolism 1,360 (0.2) Anastomotic or staple-line leak 942 (0.2) Surgical-site infection 3,767 (0.6) Postoperative length of stay 1.3 ± 1.0 Discharge Destination Home / permanent residence 620,521 (99.8) Other 4 1,328 (0.2) Footnotes 1 Other race includes Asian, American Indian or Alaska Native, Native Hawaiian or Other Pacific Islander, Some Other Race, and multiracial race combinations due to low frequency. 2 ASA classes were defined as: ASA I, normal/healthy; ASA II, mild systemic disease; ASA III, severe systemic disease; ASA IV, severe systemic disease that is a constant threat to life. 3 Serious complications include: death; unplanned intensive care unit admission; reoperation; procedural intervention; organ-space infection; pneumonia; unplanned intubation; pulmonary embolism; ventilator dependence > 48 hours; progressive renal insufficiency; acute renal failure; stroke; cardiac arrest; myocardial infarction; transfusion; deep vein thrombosis; sepsis; or septic shock. 4 Other categories of discharge destination included acute care hospital, other facility, expired, discharge against medical advice and unknown. Primary Outcome In multivariable analysis adjusted for prespecified demographic and clinical covariates, preoperative weight loss was associated with a statistically significant reduction in the odds of serious postoperative complications within 30 days (adjusted OR 0.96, 95% CI 0.92–0.99, p = 0.009) compared with no meaningful preoperative weight change (Table 2 ; Fig. 1 ). In marginal standardized analyses, this corresponded to an absolute reduction of approximately 1.1 serious complications per 1,000 patients, yielding a number needed to treat of approximately 940. The adjusted standardized risk of serious complications was approximately 2.2% among patients with no meaningful preoperative weight change versus 2.1% among those with preoperative weight loss. The association remained consistent in magnitude and direction even when excluding patients with missing venous thromboembolism prophylaxis data, confirming that the primary findings were not driven by missing covariate information. Table 2 Association between preoperative weight change and 30-day postoperative outcomes after minimally invasive sleeve gastrectomy and Roux-en-Y gastric bypass. Outcome Adjusted effect estimate 95% CI P value Primary outcome Serious complications OR 0.96 0.92–0.99 0.009 Secondary outcomes Mortality OR 0.86 0.70–1.07 0.17 Venous thromboembolism OR 0.88 0.78–0.98 0.027 Anastomotic or staple-line leak OR 0.97 0.90–1.05 0.46 Surgical-site infection OR 0.99 0.94–1.05 0.77 Gastrointestinal bleeding OR 0.95 0.87–1.04 0.27 Transfusion OR 0.96 0.88–1.05 0.36 30-day readmission OR 0.99 0.96–1.02 0.51 30-day reintervention OR 0.98 0.93–1.03 0.41 30-day reoperation OR 0.97 0.92–1.03 0.34 Length of stay (per day) IRR 0.98 0.98–0.99 < 0.001 Footnote Adjusted estimates represent the association between preoperative weight loss and postoperative outcomes, using multivariable logistic regression for binary outcomes and negative binomial regression for length of stay. Models were adjusted for age, sex, race, Hispanic ethnicity, ASA class, hypertension, cardiac history, vascular history, chronic obstructive pulmonary disease, renal insufficiency, dialysis dependence, gastroesophageal reflux disease, diabetes mellitus, hyperlipidemia, smoking status, immunosuppression, inferior vena cava filter use, history of pulmonary embolism, sleep apnea, and venous thromboembolism prophylaxis method. Odds ratios (ORs) and incidence rate ratios (IRRs) are reported with 95% confidence intervals. Abbreviations: OR, odds ratio; CI, confidence interval. Secondary Outcomes Associations between preoperative weight loss and secondary postoperative outcomes are shown in Table 2 . Preoperative weight loss was associated with a lower risk of venous thromboembolism (adjusted OR 0.88, 95% CI 0.78–0.98, p = 0.027). Preoperative weight loss was also associated with a shorter postoperative length of stay (IRR 0.98, 95% CI 0.98–0.99, p < 0.001). For other secondary outcomes, confidence intervals included the null and no clear evidence of association was observed (Table 2 ). Sensitivity Analyses Procedure-specific Analyses When stratified by procedure type, preoperative weight loss was associated with a statistically significant reduction in serious postoperative complications among patients undergoing sleeve gastrectomy (adjusted OR 0.93, 95% CI 0.89–0.98; p = 0.004). Among patients undergoing Roux-en-Y gastric bypass, the association was directionally similar but the confidence interval crossed unity (adjusted OR 0.95, 95% CI 0.90–1.01; p = 0.088). (Table 3 ; Fig. 2 ). Table 3 Sensitivity analyses for the association between preoperative weight loss and serious postoperative complications Sensitivity analysis N Adjusted OR 95% CI P value Primary analysis (overall cohort) 621,849 0.96 0.92–0.99 0.009 Sleeve gastrectomy only (CPT 43775) 451,227 0.93 0.89–0.98 0.004 Roux-en-Y gastric bypass only (CPT 43644) 170,622 0.95 0.90–1.01 0.088 Exclude robotic-assisted cases 449,103 0.92 0.88–0.96 < 0.001 Complete-case analysis (VTE prophylaxis non-missing) 603,238 0.95 0.92–0.99 0.009 BMI < 50 kg/m² 466,487 0.96 0.92–1.00 0.08 BMI ≥ 50 kg/m² 136,751 0.92 0.85–0.99 0.031 Footnotes Adjusted ORs were estimated using multivariable logistic regression with robust standard errors and prespecified covariate adjustment. Sensitivity analyses modified one analytic component at a time (procedure restriction, exclusion of robotic-assisted cases, complete-case analysis for VTE prophylaxis method, and BMI stratification < 50 vs ≥ 50 kg/m²); the exposure × BMI interaction was not statistically significant (p = 0.33). Robotic Assistance Sensitivity To assess potential confounding by operative approach, analyses excluding robotic-assisted cases were performed. In this restricted cohort, preoperative weight loss remained associated with a lower risk of serious postoperative complications (adjusted OR 0.92, 95% CI 0.88–0.96; p < 0.001), suggesting that the association was similar after excluding robotic-assisted cases (Table 3 ). Missing Data Sensitivity Meaningful missing data were limited to venous thromboembolism prophylaxis method (approximately 3%). In a complete-case sensitivity analysis excluding patients with missing prophylaxis data, the association between preoperative weight loss and serious postoperative complications remained similar in direction and magnitude to the primary analysis (Table 3 ), supporting the robustness of the primary findings. BMI Stratification In a supportive BMI-stratified sensitivity analysis, preoperative weight loss was associated with a lower risk of serious complications among patients with BMI ≥ 50 kg/m² (adjusted OR 0.92, 95% CI 0.85–0.99), whereas the association was directionally similar but not statistically significant among those with BMI < 50 kg/m² (adjusted OR 0.96, 95% CI 0.92–1.01). Formal testing did not demonstrate a statistically significant interaction between preoperative weight loss and BMI category (p for interaction = 0.33). In supportive dose–response analyses modeling continuous preoperative weight change, the association with serious postoperative complications was monotonic and directionally consistent across the observed range of weight loss (Additional File 1). Discussion In this large contemporary analysis of the MBSAQIP Participant Use File from 2020–2023, preoperative weight loss was associated with a statistically significant reduction in serious postoperative complications following minimally invasive sleeve gastrectomy and Roux-en-Y gastric bypass. This association persisted after multivariable adjustment for established preoperative risk factors and across multiple prespecified sensitivity analyses, including procedure-specific models, exclusion of robotic-assisted cases, and complete-case analyses. In addition, preoperative weight loss was associated with a lower risk of postoperative venous thromboembolism and a shorter postoperative length of stay, while estimates for mortality and other low frequency adverse events were imprecise and confidence intervals included the null. Interpretation of the Primary Finding The association between preoperative weight loss and reduced serious postoperative complications was statistically significant but corresponded to a modest absolute risk reduction. Although an absolute reduction of approximately 0.1% is small for an individual patient, when extrapolated to a national cohort exceeding 600,000 bariatric procedures, it may translate into a measurable reduction in the aggregate burden of serious postoperative morbidity. In the context of contemporary bariatric surgery—where baseline complication rates are already low—such modest relative differences are best interpreted as incremental improvements in population-level safety rather than large clinically transformative effects. The choice to focus on the MBSAQIP bariatric surgical risk/benefit calculator serious complications composite was deliberate. This outcome has been described as a clinically relevant benchmark for short-term morbidity that captures meaningful postoperative events while avoiding dilution by minor or surveillance dependent complications [ 17 ]. By anchoring the primary outcome to this established framework, the present study enables direct comparison with national risk estimates and avoids reliance on heterogeneous “any complication” composites that may obscure clinically important differences. Comparison With Prior MBSAQIP and Contemporary Studies Sun et al., using 2015–2017 MBSAQIP data, reported that even modest preoperative weight loss was associated with lower 30-day mortality, emphasizing mortality as the primary endpoint [ 11 ]. Mocanu et al. subsequently analyzed a large 2015–2018 cohort and extended the evaluation to include anastomotic leak and selected postoperative complications, again demonstrating statistically significant associations for some outcomes [ 10 ]. More recently, Saleh et al. analyzed the 2021 MBSAQIP dataset and reported heterogeneous associations between graded preoperative weight loss and multiple 30-day outcomes, with effect estimates varying by procedure type and BMI subgroup [ 19 ]. Notably, that study evaluated multiple outcome categories rather than anchoring the primary analysis to the MBSAQIP Complete-case composite, whereas the present analysis prioritizes standardized outcome benchmarking aligned with the MBSAQIP bariatric risk/benefit calculator framework. The present analysis extends prior MBSAQIP work in several important ways. First, it uses contemporary MBSAQIP data from 2020–2023, reflecting current operative techniques, perioperative pathways, and patient selection. Second, it applies a prespecified exposure definition designed to minimize measurement variability by comparing the highest recorded weight within one year prior to surgery to the weight closest to the operative date, as defined in the MBSAQIP PUF documentation [ 16 , 18 ]. Third, it evaluates outcomes using the MBSAQIP bariatric surgical risk/benefit calculator Complete-case composite, enabling clinically interpretable benchmarking within modern practice. Together, these features strengthen the relevance and interpretability of the observed associations. Consistent with prior MBSAQIP analyses, the present study evaluated BMI-stratified associations; although effect estimates appeared more pronounced among patients with BMI ≥ 50 kg/m², formal interaction testing did not demonstrate significant effect modification, and supportive dose–response analyses suggested consistent findings across the range of weight loss. Interestingly, the association was statistically significant for sleeve gastrectomy but not for Roux-en-Y gastric bypass. This may reflect reduced statistical power in the smaller bypass cohort or differences in complication profiles between procedures, some of which may be less sensitive to modest preoperative weight reduction. Mortality Findings in Context Preoperative weight loss was not independently associated with 30-day mortality in the present cohort. This finding does not contradict prior MBSAQIP studies reporting mortality associations. Instead, it reflects the extremely low absolute mortality rate in contemporary bariatric surgery, which limits statistical power to detect differences for this rare outcome. In large registry analyses, statistically significant mortality associations may emerge when event counts are sufficiently high, even when absolute risk differences are small [ 10 , 11 ]. In contrast, serious postoperative complications occur more frequently and therefore provide greater discriminatory power for evaluating perioperative risk modification strategies in current practice. Venous Thromboembolism and Physiologic Plausibility The observed reduction in postoperative venous thromboembolism among patients with preoperative weight loss is biologically plausible. Crucially, this observed reduction in thrombotic events persisted after rigorous adjustment for the specific type of venous thromboembolism prophylaxis received (mechanical, pharmacologic, or combined), suggesting that preoperative weight loss offers a risk-modifying benefit independent of standard perioperative protocols. Obesity is a well-established prothrombotic state characterized by chronic low-grade inflammation, endothelial dysfunction, impaired fibrinolysis, and increased circulating procoagulant factors, contributing to elevated perioperative venous thromboembolism risk following bariatric surgery [ 20 – 22 ]. Evidence from longitudinal cohort studies suggests that sustained weight reduction after bariatric surgery is associated with a long-term decrease in incident venous thromboembolism, despite an elevated early postoperative risk period [ 23 ]. These findings support the concept that reductions in adiposity may favorably modify thrombotic risk profiles over time. Although evidence specific to intentional preoperative weight loss is mixed, several retrospective and cohort studies have reported associations between greater preoperative weight loss and reduced overall complication rates, shorter length of stay, and improved perioperative recovery [ 12 , 24 , 25 ]. Taken together, these data provide physiologic and clinical context for the present findings, suggesting that even modest preoperative weight loss may be associated with lower thrombotic and morbidity risk in the perioperative period. Clinical and Policy Implications From a clinical perspective, the present findings support viewing preoperative weight loss as a modest risk-modifying component of perioperative optimization rather than a prerequisite for access to surgery. While the magnitude of benefit should not be overstated, the consistency of the association across analyses suggests that limited weight loss may contribute to safer short-term postoperative courses for selected patients. The high number needed to treat underscores that the absolute benefit is modest and supports encouraging weight loss for optimization without using it as a rigid requirement for eligibility. At the policy level, these results align with current professional society guidance discouraging insurance-mandated preoperative weight loss requirements. The American Society for Metabolic and Bariatric Surgery has explicitly stated that mandatory preoperative weight loss lacks sufficient evidence and may delay access to effective treatment without clear benefit [ 6 ]. The present findings support this position by demonstrating modest but consistent risk reduction. Limitations This study has several limitations inherent to retrospective registry analyses. Preoperative weight change in MBSAQIP is derived from discrete weight measurements and does not distinguish intentional dietary weight loss from unintentional change related to illness, fluid shifts, or measurement variability. However, patients with preoperative infection, sepsis, ventilator dependence, preoperative hospitalization, or other markers of acute illness were excluded to reduce the likelihood that observed weight loss reflected non-elective clinical deterioration. Residual confounding remains possible despite multivariable adjustment. Patients achieving weight loss may differ systematically in adherence, social support, or other health behaviors (“healthy user bias”), and part of the observed association may therefore reflect behavioral factors rather than physiologic effects alone. In addition, MBSAQIP captures outcomes limited to 30 days, precluding assessment of longer term morbidity or weight trajectories beyond the early postoperative period. Secondary outcomes were not adjusted for multiple comparisons and should therefore be interpreted as supportive and exploratory. Conclusions In a large contemporary national cohort of patients undergoing minimally invasive sleeve gastrectomy or Roux-en-Y gastric bypass, preoperative weight loss was associated with a statistically significant reduction in serious postoperative complications, as well as lower rates of venous thromboembolism and shorter postoperative length of stay. These findings support the role of preoperative weight loss as a component of perioperative risk optimization rather than a universal requirement for bariatric surgery and provide clinically relevant evidence to inform patient counseling and policy decisions in modern bariatric practice. Abbreviations ASA: American Society of Anesthesiologists BMI: Body mass index CI: Confidence interval CPT: Current Procedural Terminology COVID-19: Coronavirus disease 2019 HIPAA: Health Insurance Portability and Accountability Act ICU: Intensive care unit IRR: Incidence rate ratio MBSAQIP: Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program OR: Odds ratio PUF: Participant Use File RYGB: Roux-en-Y gastric bypass SD: Standard deviation STROBE: Strengthening the Reporting of Observational Studies in Epidemiology VTE: Venous thromboembolism Declarations Ethics approval and consent to participate This study used the fully de-identified Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) Participant Use File (PUF), provided by the American College of Surgeons (ACS). The PUF is a HIPAA-compliant dataset containing no direct or indirect patient identifiers. Under U.S. federal regulations (45 CFR 46.102), research using fully de-identified data does not constitute human-subjects research and therefore does not require Institutional Review Board approval or informed consent. All methods were carried out in accordance with the Declaration of Helsinki. Consent for publication Not applicable. Availability of data and materials The data that support the findings of this study are available from the American College of Surgeons MBSAQIP Participant Use File. Restrictions apply to the availability of these data, which were used under license for the current study. Derived data and analytic code are available from the corresponding author on reasonable request. Competing interests The authors declare that they have no competing interests. Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Acknowledgements Not applicable. Clinical trial number: not applicable. Use of artificial intelligence List of abbreviations AM and MR jointly conceived and designed the study. MR provided senior clinical oversight, contributed substantially to the study framework, and guided interpretation of the findings in the context of bariatric surgical practice. SHHN performed the statistical analyses and contributed to data interpretation. MT contributed to study conception and critical clinical interpretation of the results. AHL assisted with data curation and manuscript drafting. AM led manuscript preparation and revision. All authors critically revised the manuscript for important intellectual content, read, and approved the final version of the manuscript. During the preparation of this manuscript, the authors used ChatGPT (OpenAI) to assist with drafting and editing portions of the text and reviewing Python code. The authors reviewed and edited all outputs and take full responsibility for the content. Authors’ information Not applicable. 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Obes Surg. 2023;33:3–14. doi:10.1007/s11695-022-06332-1. Kim JJ, Rogers AM, Ballem N, Schirmer B; ASMBS Clinical Issues Committee. ASMBS updated position statement on insurance-mandated preoperative weight loss requirements. Surg Obes Relat Dis. 2016;12:955–959. doi:10.1016/j.soard.2016.04.019. Edholm D, Kullberg J, Haenni A, et al. Preoperative 4-week low-calorie diet reduces liver volume and intrahepatic fat and facilitates laparoscopic gastric bypass in morbidly obese patients. Obes Surg. 2011;21:345–350. doi:10.1007/s11695-010-0337-2. van Wissen J, Bakker N, Doodeman HJ, Jansma EP, Bonjer HJ, Houdijk APJ. Preoperative methods to reduce liver volume in bariatric surgery: a systematic review. Obes Surg. 2016;26:251–256. doi:10.1007/s11695-015-1769-5. Mechanick JI, Apovian C, Brethauer S, et al. Clinical practice guidelines for the perioperative nutrition, metabolic, and nonsurgical support of patients undergoing bariatric procedures: 2019 update. Surg Obes Relat Dis. 2020;16:175–247. doi:10.1016/j.soard.2019.10.025. Mocanu V, Marcil G, Dang JT, Birch DW, Switzer NJ, Karmali S. Preoperative weight loss is linked to improved mortality and leaks following elective bariatric surgery: an analysis of 548597 patients from 2015–2018. Surg Obes Relat Dis. 2021;17:1846–1853. doi:10.1016/j.soard.2021.06.021. Sun Y, Liu B, Smith JK, et al. Association of preoperative body weight and weight loss with risk of death after bariatric surgery. JAMA Netw Open. 2020;3:e204803. doi:10.1001/jamanetworkopen.2020.4803. Cassie S, Menezes C, Birch DW, Shi X, Karmali S. Effect of preoperative weight loss in bariatric surgical patients: a systematic review. Surg Obes Relat Dis. 2011;7:760–767. doi:10.1016/j.soard.2011.08.011. Esquivel MM, Azagury D. Preoperative weight loss before bariatric surgery: the debate continues. JAMA Netw Open. 2020;3:e204994. doi:10.1001/jamanetworkopen.2020.4994. Eng V, Garcia L, Khoury H, et al. Preoperative weight loss: is waiting longer before bariatric surgery more effective? Surg Obes Relat Dis. 2019;15:951–957. doi:10.1016/j.soard.2019.03.012. van Nieuwenhove Y, Dambrauskas Z, Campillo-Soto A, et al. Preoperative very low-calorie diet and operative outcome after laparoscopic gastric bypass: a randomized multicenter study. Arch Surg. 2011;146:1300–1305. doi:10.1001/archsurg.2011.273. American College of Surgeons. User guide for the 2023 Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program Participant Use Data File (PUF). Version 2. Chicago (IL): American College of Surgeons; 2024. Grieco A, Huffman KM, Cohen ME, Hall BL, Morton JM, Ko CY. The Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program bariatric surgical risk/benefit calculator: 30-day risk. Surg Obes Relat Dis. 2021;17:1117–1124. doi:10.1016/j.soard.2021.02.005. American College of Surgeons. MBSAQIP 2022 variables and definitions. Chicago (IL): American College of Surgeons; 2022. Saleh OS, Farag YMK, Medhati P, Tavakkoli A. Impact of preoperative weight loss on 30-day complication rate after bariatric surgery. J Am Coll Surg. 2024;238:993–999. doi:10.1097/XCS.0000000000001036. Blokhin IO, Lentz SR. Mechanisms of thrombosis in obesity. Curr Opin Hematol. 2013;20:437–444. doi:10.1097/MOH.0b013e3283634443. Samad F, Ruf W. Inflammation, obesity, and thrombosis. Blood. 2013;122:3415–3422. doi:10.1182/blood-2013-05-427708. Birkmeyer NJO, Finks JF, Carlin AM, et al. Risk factors for venous thromboembolism after bariatric surgery. Ann Surg. 2012;255:1100–1104. doi:10.1097/SLA.0b013e31824c04d0. Harrington LB, Benz L, Haneuse S, et al. Bariatric surgery and the long-term risk of venous thromboembolism: a population-based cohort study. Obes Surg. 2024;34:2017–2025. doi:10.1007/s11695-024-07236-y. Benotti PN, Still CD, Wood GC, et al. Preoperative weight loss before bariatric surgery. Arch Surg. 2009;144:1150–1155. doi:10.1001/archsurg.2009.209. Stenberg E, Laurenius A, Thorell A. Intentional weight reduction before surgery: a systematic review. Clin Nutr. 2025;45:156–164. doi:10.1016/j.clnu.2025.01.008. Additional Declarations No competing interests reported. Supplementary Files AdditionalFile1Copy.png Additional File 1. Dose–response association between preoperative weight change and serious postoperative complications. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8863406","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":600029253,"identity":"90890fed-a905-4634-bbfe-2aa2ad7cd4e8","order_by":0,"name":"Amir Monshizadeh","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwUlEQVRIiWNgGAWjYFACxgYQycPPwMBGmhYZyQbitUCAjcEBYrXwTzvc9oExp47H+EbyswcfKhjk+cUO4NcicTuxeQbjNjYesxtp5oYzzjAYzpydQMAaoBYGxm08QC0JZtK8bQwJBrcJaJGHaJHgMZ6R/o04LQYQLQY8BhI5RNpiCNGSwCNx5k2Z5IwzEoT9Inc7/TFQS509f3v6NokPFTby/NIEtIAA8x8QKQBWKUFYOQLwHyBF9SgYBaNgFIwkAAAKfDvlObRtNwAAAABJRU5ErkJggg==","orcid":"","institution":"Tehran University of Medical Sciences","correspondingAuthor":true,"prefix":"","firstName":"Amir","middleName":"","lastName":"Monshizadeh","suffix":""},{"id":600029254,"identity":"39a1b5bb-2551-431d-8fb8-274dccece466","order_by":1,"name":"Masoud Rezvani","email":"","orcid":"","institution":"Yale School of Medicine, Sentara Northern Virginia Medical Center","correspondingAuthor":false,"prefix":"","firstName":"Masoud","middleName":"","lastName":"Rezvani","suffix":""},{"id":600029255,"identity":"6b6de46f-8c8c-4767-ba50-49f8cdb29882","order_by":2,"name":"Mohammad Talebpour","email":"","orcid":"","institution":"Tehran University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Mohammad","middleName":"","lastName":"Talebpour","suffix":""},{"id":600029256,"identity":"425e134b-0c8a-48eb-90cf-1b9814b3445c","order_by":3,"name":"Seyed Hossein Hosseini Nourzad","email":"","orcid":"","institution":"University of Tehran","correspondingAuthor":false,"prefix":"","firstName":"Seyed","middleName":"Hossein Hosseini","lastName":"Nourzad","suffix":""},{"id":600029257,"identity":"89124f37-4656-462e-ac91-e18f1510067e","order_by":4,"name":"Amir Hossein Latif","email":"","orcid":"","institution":"Tehran University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Amir","middleName":"Hossein","lastName":"Latif","suffix":""}],"badges":[],"createdAt":"2026-02-12 14:54:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8863406/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8863406/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104405877,"identity":"de691df6-8c52-4293-bb5e-f4e5ec4c05af","added_by":"auto","created_at":"2026-03-11 12:24:02","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":150285,"visible":true,"origin":"","legend":"\u003cp\u003eAdjusted associations between preoperative weight loss and 30-day postoperative outcomes (BMI ≥35 kg/m²).\u003c/p\u003e\n\u003cp\u003eForest plot showing adjusted effect estimates for the association between preoperative weight loss (≥2.0 kg reduction) versus no meaningful preoperative weight change and 30-day postoperative outcomes after minimally invasive sleeve gastrectomy or Roux-en-Y gastric bypass. Points represent adjusted odds ratios (ORs) for binary outcomes and incidence rate ratios (IRRs) for postoperative length of stay, with horizontal lines indicating 95% confidence intervals. Estimates were derived from multivariable logistic regression models for binary outcomes and negative binomial regression for length of stay, adjusted for the prespecified covariates listed in Table 2. The vertical dashed line denotes the null effect (OR or IRR = 1.0).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8863406/v1/7bbb3177b957f81a594cbbcc.png"},{"id":104779664,"identity":"f1431f9a-056c-466a-bd9d-b9fff2e654e9","added_by":"auto","created_at":"2026-03-17 07:44:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":134290,"visible":true,"origin":"","legend":"\u003cp\u003eSensitivity analyses for the association between preoperative weight loss and serious postoperative complications in patients with body mass index ≥35 kg/m².\u003c/p\u003e\n\u003cp\u003eForest plot showing adjusted odds ratios (ORs) and 95% confidence intervals for serious postoperative complications comparing preoperative weight loss versus no meaningful preoperative weight change across prespecified sensitivity analyses, including procedure-specific models (sleeve gastrectomy and Roux-en-Y gastric bypass), exclusion of robotic-assisted cases, complete-case analysis excluding patients with missing venous thromboembolism prophylaxis data, and BMI-stratified models (\u0026lt;50 vs ≥50 kg/m²). All models used identical covariate adjustment as the primary analysis. The vertical dashed line indicates the null effect (OR = 1.0).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8863406/v1/005c8842cfe8a412763b8f26.png"},{"id":108803936,"identity":"203a5c12-fde1-4c00-af36-995ac864fe3d","added_by":"auto","created_at":"2026-05-08 15:11:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":576580,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8863406/v1/ed703351-eb52-4854-9d89-e1cab455b7d3.pdf"},{"id":104341495,"identity":"907db47d-44f2-45a2-ab66-4a2de2079550","added_by":"auto","created_at":"2026-03-10 16:49:51","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":247862,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAdditional File 1. \u003c/strong\u003eDose–response association between preoperative weight change and serious postoperative complications.\u003c/p\u003e","description":"","filename":"AdditionalFile1Copy.png","url":"https://assets-eu.researchsquare.com/files/rs-8863406/v1/85062113969afc9fe3442c81.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Association of Modest Preoperative Weight Loss and 30-Day Outcomes After Bariatric Surgery: A Contemporary MBSAQIP Analysis","fulltext":[{"header":"Background","content":"\u003cp\u003eObesity is a major global public health challenge, affecting more than 890\u0026nbsp;million adults worldwide and contributing substantially to preventable morbidity, mortality, and healthcare expenditures [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Metabolic and bariatric surgery remains the most effective and durable treatment for severe obesity, producing sustained weight loss and significant improvement in obesity-related comorbidities, including type 2 diabetes [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Despite these benefits, bariatric surgery carries inherent perioperative risks, underscoring the importance of identifying modifiable preoperative factors that may influence short-term postoperative outcomes.\u003c/p\u003e \u003cp\u003ePreoperative weight loss is commonly encouraged\u0026mdash;and in some settings required by insurers or clinical pathways\u0026mdash;based on the premise that modest weight reduction may improve perioperative outcomes [\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. However, the value of preoperative weight loss for reducing short-term postoperative morbidity remains incompletely defined. Prior studies have reported heterogeneous associations, with effect estimates varying by procedure type, exposure definition, and outcome selection [\u003cspan additionalcitationids=\"CR11 CR12\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. As a result, the clinical relevance of preoperative weight loss remains debated, and mandatory requirements persist despite inconsistent evidence.\u003c/p\u003e \u003cp\u003eLarge registry-based analyses using MBSAQIP have improved statistical power and outcome ascertainment, yet uncertainty persists regarding the magnitude and consistency of the association between preoperative weight loss and short-term postoperative outcomes in contemporary practice [\u003cspan additionalcitationids=\"CR11 CR12 CR13\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. In parallel, smaller interventional studies of preoperative dietary regimens (e.g., very-low-calorie diets) suggest potential perioperative technical benefits, but do not fully resolve questions about short-term morbidity in contemporary registry-based practice [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Differences in exposure definitions and outcome selection\u0026mdash;often emphasizing mortality or isolated complications rather than standardized morbidity composites\u0026mdash;have limited comparability across studies and contributed to ongoing debate [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAccordingly, we performed a contemporary analysis of the MBSAQIP Participant Use File from 2020 to 2023 to evaluate the association between modest preoperative weight loss and 30-day postoperative outcomes following minimally invasive sleeve gastrectomy and Roux-en-Y gastric bypass. Our primary objective was to quantify the association between preoperative weight loss and serious postoperative complications, defined using the MBSAQIP bariatric surgical risk/benefit calculator composite [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], using a large national cohort from the MBSAQIP Participant Use File [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy Design and Data Source\u003c/h2\u003e \u003cp\u003eWe conducted a retrospective cohort study using the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) Participant Use File (PUF) from 2020 to 2023. MBSAQIP is a national clinical registry that uses prospective, standardized data collection to capture perioperative variables and 30-day postoperative outcomes [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The dataset is fully de-identified; therefore, this study was exempt from institutional review board oversight.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eCohort Selection and Preprocessing\u003c/h3\u003e\n\u003cp\u003ePatients undergoing minimally invasive sleeve gastrectomy or Roux-en-Y gastric bypass were identified using Current Procedural Terminology (CPT) codes 43775 and 43644, respectively. Patients with a preoperative body mass index\u0026thinsp;\u0026lt;\u0026thinsp;35 kg/m\u0026sup2; were excluded. To restrict the cohort to elective primary bariatric procedures and ensure consistent attribution of postoperative outcomes, we excluded non\u0026ndash;minimally invasive approaches, revision or conversion operations, cases with incomplete 30-day follow-up, American Society of Anesthesiologists (ASA) physical status class V, and patients with a preoperative hospital length of stay greater than zero days.\u003c/p\u003e \u003cp\u003eAdditional exclusions were applied to minimize confounding from acute illness or perioperative instability, including preoperative infection, sepsis or septic shock, pneumonia, ventilator dependence, confirmed or suspected preoperative COVID-19 infection, and missing postoperative length of stay. Patients with missing ASA class were excluded given its central role in risk adjustment. Age was restricted to 13\u0026ndash;80 years because MBSAQIP top- and bottom-codes ages outside this range for de-identification, limiting interpretability of age as a continuous covariate in risk-adjusted models [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Cases with unknown sex designation were excluded during initial data quality checks to harmonize variable coding.\u003c/p\u003e\n\u003ch3\u003eExposure Definition\u003c/h3\u003e\n\u003cp\u003eThe primary exposure was preoperative weight change, derived from registry-recorded anthropometric measurements. Weight change was calculated as the difference between the weight recorded closest to the operative date and the highest weight recorded within one year prior to surgery, as specified in the MBSAQIP Participant Use File [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. For all primary analyses, a prespecified categorical exposure variable was used, classifying patients as having preoperative weight loss (\u0026ge;\u0026thinsp;2.0 kg reduction) or no meaningful preoperative weight change (\u0026minus;\u0026thinsp;2.0 to +\u0026thinsp;2.0 kg). The 2.0 kg threshold was selected a priori to exceed routine scale-related and day-to-day weight fluctuation and to distinguish modest, clinically relevant weight reduction from measurement noise in registry data. Because the MBSAQIP variable anchors weight change to the highest recorded weight within the preceding year, meaningful preoperative weight gain could not be consistently distinguished in this dataset. Therefore, analyses focused on the comparison between modest preoperative weight loss and weight stability.\u003c/p\u003e\n\u003ch3\u003eCovariates\u003c/h3\u003e\n\u003cp\u003ePrespecified preoperative covariates included age, sex, race, Hispanic ethnicity, American Society of Anesthesiologists (ASA) physical status (I\u0026ndash;II, III, or IV), hypertension, chronic obstructive pulmonary disease, obstructive sleep apnea, smoking status, diabetes mellitus, hyperlipidemia, renal insufficiency, dialysis dependence, gastroesophageal reflux disease, prior pulmonary embolism, immunosuppression, and inferior vena cava filter use. Race was modeled as a three-category variable (White, Black or African American, and Other), with the \u0026ldquo;Other\u0026rdquo; category combining less frequent racial groups to ensure stable multivariable estimates.\u003c/p\u003e \u003cp\u003eTwo composite variables were constructed in accordance with the MBSAQIP bariatric surgical risk/benefit calculator framework: cardiac history (history of myocardial infarction, percutaneous coronary intervention, or prior cardiac surgery) and vascular history (history of venous stasis, venous thromboembolism requiring therapy, or therapeutic anticoagulation) [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eVenous thromboembolism prophylaxis method was modeled as a three-level categorical variable (mechanical only, pharmacologic only, or combined mechanical and pharmacologic). Missing data were minimal and were primarily limited to prophylaxis method, which was retained as an explicit category in the primary analysis and evaluated using complete-case sensitivity analyses.\u003c/p\u003e\n\u003ch3\u003eOutcomes\u003c/h3\u003e\n\u003cp\u003eThe primary outcome was serious postoperative complications within 30 days, defined identically to the MBSAQIP bariatric surgical risk/benefit calculator as the occurrence of one or more of the following: death; unplanned intensive care unit admission; reoperation; procedural intervention; organ-space infection; pneumonia; unplanned intubation; pulmonary embolism; ventilator dependence\u0026thinsp;\u0026gt;\u0026thinsp;48 hours; progressive renal insufficiency; acute renal failure; stroke; cardiac arrest; myocardial infarction; transfusion; deep vein thrombosis; sepsis; or septic shock [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. This composite outcome was selected a priori to enable standardized benchmarking against national MBSAQIP risk estimates.\u003c/p\u003e \u003cp\u003eSecondary outcomes included mortality, venous thromboembolism, anastomotic or staple-line leak, 30-day readmission, reoperation, non-operative intervention, gastrointestinal bleeding, transfusion, surgical-site infection (superficial, deep, and organ space), and postoperative length of stay [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analysis\u003c/h2\u003e \u003cp\u003eBinary outcomes were analyzed using multivariable logistic regression and are reported as adjusted odds ratios (ORs) with 95% confidence intervals. Postoperative length of stay was analyzed using negative binomial regression and is reported as an incidence rate ratio (IRR) with 95% confidence intervals to account for right skewed and over dispersed count data. Robust standard errors were used for all models.\u003c/p\u003e \u003cp\u003eThe exposure was modeled as a binary comparison of preoperative weight loss versus no meaningful preoperative weight change, with only one exposure representation included per model. All prespecified covariates were entered simultaneously. Statistical significance was defined as a two-sided p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003eTo enhance clinical interpretability, marginal standardized risks were derived from the primary model to estimate adjusted absolute risk differences and numbers needed to treat. Prespecified supportive analyses included BMI-stratified models (\u0026lt;\u0026thinsp;50 vs\u0026thinsp;\u0026ge;\u0026thinsp;50 kg/m\u0026sup2;) with formal interaction testing and E-value analysis to assess robustness to unmeasured confounding. These analyses did not alter the primary exposure or outcome definitions. Supportive dose\u0026ndash;response analyses modeled continuous preoperative weight change using restricted cubic splines.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSensitivity Analyses\u003c/h3\u003e\n\u003cp\u003ePrespecified sensitivity analyses were performed to assess the robustness of the association between preoperative weight loss and serious postoperative complications. These included stratified analyses by procedure type (sleeve gastrectomy versus Roux-en-Y gastric bypass), exclusion of robotic-assisted cases, and a complete-case sensitivity analysis excluding patients with missing values for venous thromboembolism prophylaxis method. In the primary analysis, missing values for venous thromboembolism prophylaxis method were retained as an explicit category. All sensitivity analyses used identical model specifications and covariate adjustment as the primary analysis.\u003c/p\u003e\n\u003ch3\u003eSoftware\u003c/h3\u003e\n\u003cp\u003eAnalyses were performed using Python (version 3.12.12), including pandas (version 2.2.2) and statsmodels (version 0.14.6).\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eStudy Cohort\u003c/h2\u003e \u003cp\u003eThe MBSAQIP Participant Use File from 2020\u0026ndash;2023 initially included 828,481 cases. After application of prespecified exclusion criteria and data cleaning, a total of 621,849 patients constituted the final analytic cohort. Of these, 451,227 (72.6%) underwent minimally invasive sleeve gastrectomy (CPT 43775), and 170,622 (27.4%) underwent minimally invasive Roux-en-Y gastric bypass (CPT 43644). Baseline demographic characteristics, comorbidities, perioperative features, and postoperative outcomes for the overall cohort are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Preoperative weight loss was common, with 423,962 patients (68.2%) classified as having experienced preoperative weight loss and 197,887 (31.8%) classified as having no meaningful preoperative weight change. Among patients with preoperative weight loss, the mean weight change was \u0026minus;\u0026thinsp;7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;5.8 kg, reflecting heterogeneity in the magnitude of weight loss.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBaseline characteristics, operative details, and 30-day outcomes of patients undergoing primary minimally invasive bariatric surgery with BMI\u0026thinsp;\u0026ge;\u0026thinsp;35 kg/m\u0026sup2; (N\u0026thinsp;=\u0026thinsp;621,849).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eValue (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD or N [%])\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDemographics\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e43.0\u0026thinsp;\u0026plusmn;\u0026thinsp;11.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBody mass index (kg/m\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e45.6\u0026thinsp;\u0026plusmn;\u0026thinsp;7.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemale sex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e510,438 (82.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eRace\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWhite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e398,572 (64.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBlack / African American\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e127,525 (20.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOther\u0026sup1;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e95,752 (15.4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHispanic ethnicity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e109,345 (17.6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFunctional status\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFunctionally independent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e618,282 (99.43)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNot independent (partial, total, or missing)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3,567 (0.57)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eASA class\u0026sup2;\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eASA I\u0026ndash;II\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e108,164 (17.4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eASA III\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e492,279 (79.2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eASA IV\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21,406 (3.4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eVTE prophylaxis method\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMechanical and pharmacologic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e552,929 (88.9%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMechanical only\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e41,503 (6.7%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePharmacologic only\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8,806 (1.4%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMissing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18,611 (3.0%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePreoperative weight change\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePreoperative weight loss\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e423,962 (68.2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo meaningful weight change\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e197,887 (31.8)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWeight change (kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026minus;7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;5.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eComorbidities\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiabetes mellitus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e143,022 (23.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHypertension\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e271,976 (43.7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSleep apnea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e234,046 (37.6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGastroesophageal reflux disease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e184,684 (29.7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChronic obstructive pulmonary disease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7,022 (1.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRenal insufficiency\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3,214 (0.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHyperlipidemia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e138,793 (22.3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eImmunosuppression\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14,031 (2.3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmoker\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40,121 (6.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInferior vena cava filter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1,194 (0.2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOn dialysis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1,905 (0.3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCardiac history\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13,253 (2.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVascular history\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26,692 (4.3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHistory of pulmonary embolism\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8,535 (1.4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSurgical and intraoperative information\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMinimally invasive sleeve gastrectomy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e451,227 (72.6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMinimally invasive Roux-en-Y gastric bypass\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e170,622 (27.4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRobotic assistance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e172,746 (27.8)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e30-day outcomes\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSerious complications\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13,162 (2.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMortality\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e426 (0.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e30-day readmission\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17,884 (2.9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e30-day reoperation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5,452 (0.9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e30-day reintervention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4,211 (0.7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTransfusion\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3,797 (0.61)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGastrointestinal bleeding\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2,349 (0.38)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVenous thromboembolism\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1,360 (0.2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnastomotic or staple-line leak\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e942 (0.2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSurgical-site infection\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3,767 (0.6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePostoperative length of stay\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eDischarge Destination\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHome / permanent residence\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e620,521 (99.8)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOther \u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1,328 (0.2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e\u003cb\u003eFootnotes\u003c/b\u003e\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e1 Other race includes Asian, American Indian or Alaska Native, Native Hawaiian or Other Pacific Islander, Some Other Race, and multiracial race combinations due to low frequency.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e2 ASA classes were defined as: ASA I, normal/healthy; ASA II, mild systemic disease; ASA III, severe systemic disease; ASA IV, severe systemic disease that is a constant threat to life.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e3 Serious complications include: death; unplanned intensive care unit admission; reoperation; procedural intervention; organ-space infection; pneumonia; unplanned intubation; pulmonary embolism; ventilator dependence\u0026thinsp;\u0026gt;\u0026thinsp;48 hours; progressive renal insufficiency; acute renal failure; stroke; cardiac arrest; myocardial infarction; transfusion; deep vein thrombosis; sepsis; or septic shock.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e4 Other categories of discharge destination included acute care hospital, other facility, expired, discharge against medical advice and unknown.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003ePrimary Outcome\u003c/h2\u003e \u003cp\u003eIn multivariable analysis adjusted for prespecified demographic and clinical covariates, preoperative weight loss was associated with a statistically significant reduction in the odds of serious postoperative complications within 30 days (adjusted OR 0.96, 95% CI 0.92\u0026ndash;0.99, p\u0026thinsp;=\u0026thinsp;0.009) compared with no meaningful preoperative weight change (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In marginal standardized analyses, this corresponded to an absolute reduction of approximately 1.1 serious complications per 1,000 patients, yielding a number needed to treat of approximately 940. The adjusted standardized risk of serious complications was approximately 2.2% among patients with no meaningful preoperative weight change versus 2.1% among those with preoperative weight loss. The association remained consistent in magnitude and direction even when excluding patients with missing venous thromboembolism prophylaxis data, confirming that the primary findings were not driven by missing covariate information.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAssociation between preoperative weight change and 30-day postoperative outcomes after minimally invasive sleeve gastrectomy and Roux-en-Y gastric bypass.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOutcome\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAdjusted effect estimate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e95% CI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eP value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePrimary outcome\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSerious complications\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR 0.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.92\u0026ndash;0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.009\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSecondary outcomes\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMortality\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR 0.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.70\u0026ndash;1.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVenous thromboembolism\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR 0.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.78\u0026ndash;0.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.027\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnastomotic or staple-line leak\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR 0.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.90\u0026ndash;1.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.46\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSurgical-site infection\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR 0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.94\u0026ndash;1.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.77\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGastrointestinal bleeding\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR 0.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.87\u0026ndash;1.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.27\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTransfusion\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR 0.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.88\u0026ndash;1.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.36\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e30-day readmission\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR 0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.96\u0026ndash;1.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e30-day reintervention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR 0.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.93\u0026ndash;1.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.41\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e30-day reoperation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR 0.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.92\u0026ndash;1.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLength of stay (per day)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIRR 0.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.98\u0026ndash;0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003cb\u003eFootnote\u003c/b\u003e\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eAdjusted estimates represent the association between preoperative weight loss and postoperative outcomes, using multivariable logistic regression for binary outcomes and negative binomial regression for length of stay. Models were adjusted for age, sex, race, Hispanic ethnicity, ASA class, hypertension, cardiac history, vascular history, chronic obstructive pulmonary disease, renal insufficiency, dialysis dependence, gastroesophageal reflux disease, diabetes mellitus, hyperlipidemia, smoking status, immunosuppression, inferior vena cava filter use, history of pulmonary embolism, sleep apnea, and venous thromboembolism prophylaxis method. Odds ratios (ORs) and incidence rate ratios (IRRs) are reported with 95% confidence intervals. Abbreviations: OR, odds ratio; CI, confidence interval.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eSecondary Outcomes\u003c/h2\u003e \u003cp\u003eAssociations between preoperative weight loss and secondary postoperative outcomes are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Preoperative weight loss was associated with a lower risk of venous thromboembolism (adjusted OR 0.88, 95% CI 0.78\u0026ndash;0.98, p\u0026thinsp;=\u0026thinsp;0.027). Preoperative weight loss was also associated with a shorter postoperative length of stay (IRR 0.98, 95% CI 0.98\u0026ndash;0.99, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). For other secondary outcomes, confidence intervals included the null and no clear evidence of association was observed (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eSensitivity Analyses\u003c/h2\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003eProcedure-specific Analyses\u003c/h2\u003e \u003cp\u003eWhen stratified by procedure type, preoperative weight loss was associated with a statistically significant reduction in serious postoperative complications among patients undergoing sleeve gastrectomy (adjusted OR 0.93, 95% CI 0.89\u0026ndash;0.98; p\u0026thinsp;=\u0026thinsp;0.004). Among patients undergoing Roux-en-Y gastric bypass, the association was directionally similar but the confidence interval crossed unity (adjusted OR 0.95, 95% CI 0.90\u0026ndash;1.01; p\u0026thinsp;=\u0026thinsp;0.088). (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSensitivity analyses for the association between preoperative weight loss and serious postoperative complications\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSensitivity analysis\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAdjusted OR\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e95% CI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eP value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePrimary analysis (overall cohort)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e621,849\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.92\u0026ndash;0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.009\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSleeve gastrectomy only (CPT 43775)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e451,227\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.89\u0026ndash;0.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.004\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRoux-en-Y gastric bypass only (CPT 43644)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e170,622\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.90\u0026ndash;1.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.088\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExclude robotic-assisted cases\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e449,103\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.88\u0026ndash;0.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComplete-case analysis (VTE prophylaxis non-missing)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e603,238\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.92\u0026ndash;0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.009\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI\u0026thinsp;\u0026lt;\u0026thinsp;50 kg/m\u0026sup2;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e466,487\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.92\u0026ndash;1.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI\u0026thinsp;\u0026ge;\u0026thinsp;50 kg/m\u0026sup2;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e136,751\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.85\u0026ndash;0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.031\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003cb\u003eFootnotes\u003c/b\u003e\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eAdjusted ORs were estimated using multivariable logistic regression with robust standard errors and prespecified covariate adjustment. Sensitivity analyses modified one analytic component at a time (procedure restriction, exclusion of robotic-assisted cases, complete-case analysis for VTE prophylaxis method, and BMI stratification\u0026thinsp;\u0026lt;\u0026thinsp;50 vs\u0026thinsp;\u0026ge;\u0026thinsp;50 kg/m\u0026sup2;); the exposure \u0026times; BMI interaction was not statistically significant (p\u0026thinsp;=\u0026thinsp;0.33).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eRobotic Assistance Sensitivity\u003c/h2\u003e \u003cp\u003eTo assess potential confounding by operative approach, analyses excluding robotic-assisted cases were performed. In this restricted cohort, preoperative weight loss remained associated with a lower risk of serious postoperative complications (adjusted OR 0.92, 95% CI 0.88\u0026ndash;0.96; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), suggesting that the association was similar after excluding robotic-assisted cases (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eMissing Data Sensitivity\u003c/h2\u003e \u003cp\u003eMeaningful missing data were limited to venous thromboembolism prophylaxis method (approximately 3%). In a complete-case sensitivity analysis excluding patients with missing prophylaxis data, the association between preoperative weight loss and serious postoperative complications remained similar in direction and magnitude to the primary analysis (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), supporting the robustness of the primary findings.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eBMI Stratification\u003c/h2\u003e \u003cp\u003eIn a supportive BMI-stratified sensitivity analysis, preoperative weight loss was associated with a lower risk of serious complications among patients with BMI\u0026thinsp;\u0026ge;\u0026thinsp;50 kg/m\u0026sup2; (adjusted OR 0.92, 95% CI 0.85\u0026ndash;0.99), whereas the association was directionally similar but not statistically significant among those with BMI\u0026thinsp;\u0026lt;\u0026thinsp;50 kg/m\u0026sup2; (adjusted OR 0.96, 95% CI 0.92\u0026ndash;1.01). Formal testing did not demonstrate a statistically significant interaction between preoperative weight loss and BMI category (p for interaction\u0026thinsp;=\u0026thinsp;0.33). In supportive dose\u0026ndash;response analyses modeling continuous preoperative weight change, the association with serious postoperative complications was monotonic and directionally consistent across the observed range of weight loss (Additional File 1).\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this large contemporary analysis of the MBSAQIP Participant Use File from 2020\u0026ndash;2023, preoperative weight loss was associated with a statistically significant reduction in serious postoperative complications following minimally invasive sleeve gastrectomy and Roux-en-Y gastric bypass. This association persisted after multivariable adjustment for established preoperative risk factors and across multiple prespecified sensitivity analyses, including procedure-specific models, exclusion of robotic-assisted cases, and complete-case analyses. In addition, preoperative weight loss was associated with a lower risk of postoperative venous thromboembolism and a shorter postoperative length of stay, while estimates for mortality and other low frequency adverse events were imprecise and confidence intervals included the null.\u003c/p\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eInterpretation of the Primary Finding\u003c/h2\u003e \u003cp\u003eThe association between preoperative weight loss and reduced serious postoperative complications was statistically significant but corresponded to a modest absolute risk reduction. Although an absolute reduction of approximately 0.1% is small for an individual patient, when extrapolated to a national cohort exceeding 600,000 bariatric procedures, it may translate into a measurable reduction in the aggregate burden of serious postoperative morbidity. In the context of contemporary bariatric surgery\u0026mdash;where baseline complication rates are already low\u0026mdash;such modest relative differences are best interpreted as incremental improvements in population-level safety rather than large clinically transformative effects.\u003c/p\u003e \u003cp\u003eThe choice to focus on the MBSAQIP bariatric surgical risk/benefit calculator serious complications composite was deliberate. This outcome has been described as a clinically relevant benchmark for short-term morbidity that captures meaningful postoperative events while avoiding dilution by minor or surveillance dependent complications [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. By anchoring the primary outcome to this established framework, the present study enables direct comparison with national risk estimates and avoids reliance on heterogeneous \u0026ldquo;any complication\u0026rdquo; composites that may obscure clinically important differences.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eComparison With Prior MBSAQIP and Contemporary Studies\u003c/h2\u003e \u003cp\u003eSun et al., using 2015\u0026ndash;2017 MBSAQIP data, reported that even modest preoperative weight loss was associated with lower 30-day mortality, emphasizing mortality as the primary endpoint [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Mocanu et al. subsequently analyzed a large 2015\u0026ndash;2018 cohort and extended the evaluation to include anastomotic leak and selected postoperative complications, again demonstrating statistically significant associations for some outcomes [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMore recently, Saleh et al. analyzed the 2021 MBSAQIP dataset and reported heterogeneous associations between graded preoperative weight loss and multiple 30-day outcomes, with effect estimates varying by procedure type and BMI subgroup [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Notably, that study evaluated multiple outcome categories rather than anchoring the primary analysis to the MBSAQIP Complete-case composite, whereas the present analysis prioritizes standardized outcome benchmarking aligned with the MBSAQIP bariatric risk/benefit calculator framework.\u003c/p\u003e \u003cp\u003eThe present analysis extends prior MBSAQIP work in several important ways. First, it uses contemporary MBSAQIP data from 2020\u0026ndash;2023, reflecting current operative techniques, perioperative pathways, and patient selection. Second, it applies a prespecified exposure definition designed to minimize measurement variability by comparing the highest recorded weight within one year prior to surgery to the weight closest to the operative date, as defined in the MBSAQIP PUF documentation [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Third, it evaluates outcomes using the MBSAQIP bariatric surgical risk/benefit calculator Complete-case composite, enabling clinically interpretable benchmarking within modern practice. Together, these features strengthen the relevance and interpretability of the observed associations. Consistent with prior MBSAQIP analyses, the present study evaluated BMI-stratified associations; although effect estimates appeared more pronounced among patients with BMI\u0026thinsp;\u0026ge;\u0026thinsp;50 kg/m\u0026sup2;, formal interaction testing did not demonstrate significant effect modification, and supportive dose\u0026ndash;response analyses suggested consistent findings across the range of weight loss.\u003c/p\u003e \u003cp\u003eInterestingly, the association was statistically significant for sleeve gastrectomy but not for Roux-en-Y gastric bypass. This may reflect reduced statistical power in the smaller bypass cohort or differences in complication profiles between procedures, some of which may be less sensitive to modest preoperative weight reduction.\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eMortality Findings in Context\u003c/h2\u003e \u003cp\u003ePreoperative weight loss was not independently associated with 30-day mortality in the present cohort. This finding does not contradict prior MBSAQIP studies reporting mortality associations. Instead, it reflects the extremely low absolute mortality rate in contemporary bariatric surgery, which limits statistical power to detect differences for this rare outcome. In large registry analyses, statistically significant mortality associations may emerge when event counts are sufficiently high, even when absolute risk differences are small [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. In contrast, serious postoperative complications occur more frequently and therefore provide greater discriminatory power for evaluating perioperative risk modification strategies in current practice.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003eVenous Thromboembolism and Physiologic Plausibility\u003c/h2\u003e \u003cp\u003eThe observed reduction in postoperative venous thromboembolism among patients with preoperative weight loss is biologically plausible. Crucially, this observed reduction in thrombotic events persisted after rigorous adjustment for the specific type of venous thromboembolism prophylaxis received (mechanical, pharmacologic, or combined), suggesting that preoperative weight loss offers a risk-modifying benefit independent of standard perioperative protocols. Obesity is a well-established prothrombotic state characterized by chronic low-grade inflammation, endothelial dysfunction, impaired fibrinolysis, and increased circulating procoagulant factors, contributing to elevated perioperative venous thromboembolism risk following bariatric surgery [\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eEvidence from longitudinal cohort studies suggests that sustained weight reduction after bariatric surgery is associated with a long-term decrease in incident venous thromboembolism, despite an elevated early postoperative risk period [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. These findings support the concept that reductions in adiposity may favorably modify thrombotic risk profiles over time. Although evidence specific to intentional preoperative weight loss is mixed, several retrospective and cohort studies have reported associations between greater preoperative weight loss and reduced overall complication rates, shorter length of stay, and improved perioperative recovery [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Taken together, these data provide physiologic and clinical context for the present findings, suggesting that even modest preoperative weight loss may be associated with lower thrombotic and morbidity risk in the perioperative period.\u003c/p\u003e \u003cdiv id=\"Sec25\" class=\"Section3\"\u003e \u003ch2\u003eClinical and Policy Implications\u003c/h2\u003e \u003cp\u003eFrom a clinical perspective, the present findings support viewing preoperative weight loss as a modest risk-modifying component of perioperative optimization rather than a prerequisite for access to surgery. While the magnitude of benefit should not be overstated, the consistency of the association across analyses suggests that limited weight loss may contribute to safer short-term postoperative courses for selected patients. The high number needed to treat underscores that the absolute benefit is modest and supports encouraging weight loss for optimization without using it as a rigid requirement for eligibility.\u003c/p\u003e \u003cp\u003eAt the policy level, these results align with current professional society guidance discouraging insurance-mandated preoperative weight loss requirements. The American Society for Metabolic and Bariatric Surgery has explicitly stated that mandatory preoperative weight loss lacks sufficient evidence and may delay access to effective treatment without clear benefit [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The present findings support this position by demonstrating modest but consistent risk reduction.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section3\"\u003e \u003ch2\u003eLimitations\u003c/h2\u003e \u003cp\u003eThis study has several limitations inherent to retrospective registry analyses. Preoperative weight change in MBSAQIP is derived from discrete weight measurements and does not distinguish intentional dietary weight loss from unintentional change related to illness, fluid shifts, or measurement variability. However, patients with preoperative infection, sepsis, ventilator dependence, preoperative hospitalization, or other markers of acute illness were excluded to reduce the likelihood that observed weight loss reflected non-elective clinical deterioration. Residual confounding remains possible despite multivariable adjustment. Patients achieving weight loss may differ systematically in adherence, social support, or other health behaviors (\u0026ldquo;healthy user bias\u0026rdquo;), and part of the observed association may therefore reflect behavioral factors rather than physiologic effects alone. In addition, MBSAQIP captures outcomes limited to 30 days, precluding assessment of longer term morbidity or weight trajectories beyond the early postoperative period. Secondary outcomes were not adjusted for multiple comparisons and should therefore be interpreted as supportive and exploratory.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn a large contemporary national cohort of patients undergoing minimally invasive sleeve gastrectomy or Roux-en-Y gastric bypass, preoperative weight loss was associated with a statistically significant reduction in serious postoperative complications, as well as lower rates of venous thromboembolism and shorter postoperative length of stay. These findings support the role of preoperative weight loss as a component of perioperative risk optimization rather than a universal requirement for bariatric surgery and provide clinically relevant evidence to inform patient counseling and policy decisions in modern bariatric practice.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eASA: American Society of Anesthesiologists\u003cbr\u003e\u0026nbsp;BMI: Body mass index\u003cbr\u003e\u0026nbsp;CI: Confidence interval\u003cbr\u003e\u0026nbsp;CPT: Current Procedural Terminology\u003cbr\u003e\u0026nbsp;COVID-19: Coronavirus disease 2019\u003cbr\u003e\u0026nbsp;HIPAA: Health Insurance Portability and Accountability Act\u003cbr\u003e\u0026nbsp;ICU: Intensive care unit\u003cbr\u003e\u0026nbsp;IRR: Incidence rate ratio\u003cbr\u003e\u0026nbsp;MBSAQIP: Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program\u003cbr\u003e\u0026nbsp;OR: Odds ratio\u003cbr\u003e\u0026nbsp;PUF: Participant Use File\u003cbr\u003e\u0026nbsp;RYGB: Roux-en-Y gastric bypass\u003cbr\u003e\u0026nbsp;SD: Standard deviation\u003cbr\u003e\u0026nbsp;STROBE: Strengthening the Reporting of Observational Studies in Epidemiology\u003cbr\u003e\u0026nbsp;VTE: Venous thromboembolism\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study used the fully de-identified Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) Participant Use File (PUF), provided by the American College of Surgeons (ACS). The PUF is a HIPAA-compliant dataset containing no direct or indirect patient identifiers. Under U.S. federal regulations (45 CFR 46.102), research using fully de-identified data does not constitute human-subjects research and therefore does not require Institutional Review Board approval or informed consent. All methods were carried out in accordance with the Declaration of Helsinki.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the American College of Surgeons MBSAQIP Participant Use File. Restrictions apply to the availability of these data, which were used under license for the current study. Derived data and analytic code are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number:\u0026nbsp;\u003c/strong\u003enot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUse of artificial intelligence\u003c/strong\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eList of abbreviations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAM and MR jointly conceived and designed the study. MR provided senior clinical oversight, contributed substantially to the study framework, and guided interpretation of the findings in the context of bariatric surgical practice. SHHN performed the statistical analyses and contributed to data interpretation. MT contributed to study conception and critical clinical interpretation of the results. AHL assisted with data curation and manuscript drafting. AM led manuscript preparation and revision. All authors critically revised the manuscript for important intellectual content, read, and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003eDuring the preparation of this manuscript, the authors used ChatGPT (OpenAI) to assist with drafting and editing portions of the text and reviewing Python code. The authors reviewed and edited all outputs and take full responsibility for the content.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors’ information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWorld Health Organization. Obesity and overweight. https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight. Accessed 30 Jan 2025.\u003c/li\u003e\n\u003cli\u003eGBD 2019 Risk Factors Collaborators. Global burden of 87 risk factors in 204 countries and territories, 1990\u0026ndash;2019: a systematic analysis for the Global Burden of Disease Study 2019. Lancet. 2020;396:1223\u0026ndash;1249. doi:10.1016/S0140-6736(20)30752-2.\u003c/li\u003e\n\u003cli\u003eCawley J, Meyerhoefer C. The medical care costs of obesity: an instrumental variables approach. J Health Econ. 2012;31:219\u0026ndash;230. doi:10.1016/j.jhealeco.2011.10.003.\u003c/li\u003e\n\u003cli\u003eSchauer PR, Bhatt DL, Kirwan JP, et al. Bariatric surgery versus intensive medical therapy for diabetes: 5-year outcomes. N Engl J Med. 2017;376:641\u0026ndash;651. doi:10.1056/NEJMoa1600869.\u003c/li\u003e\n\u003cli\u003eEisenberg D, Shikora SA, Aarts E, et al. 2022 American Society for Metabolic and Bariatric Surgery and International Federation for the Surgery of Obesity and Metabolic Disorders indications for metabolic and bariatric surgery. Obes Surg. 2023;33:3\u0026ndash;14. doi:10.1007/s11695-022-06332-1.\u003c/li\u003e\n\u003cli\u003eKim JJ, Rogers AM, Ballem N, Schirmer B; ASMBS Clinical Issues Committee. ASMBS updated position statement on insurance-mandated preoperative weight loss requirements. Surg Obes Relat Dis. 2016;12:955\u0026ndash;959. doi:10.1016/j.soard.2016.04.019.\u003c/li\u003e\n\u003cli\u003eEdholm D, Kullberg J, Haenni A, et al. Preoperative 4-week low-calorie diet reduces liver volume and intrahepatic fat and facilitates laparoscopic gastric bypass in morbidly obese patients. Obes Surg. 2011;21:345\u0026ndash;350. doi:10.1007/s11695-010-0337-2.\u003c/li\u003e\n\u003cli\u003evan Wissen J, Bakker N, Doodeman HJ, Jansma EP, Bonjer HJ, Houdijk APJ. Preoperative methods to reduce liver volume in bariatric surgery: a systematic review. Obes Surg. 2016;26:251\u0026ndash;256. doi:10.1007/s11695-015-1769-5.\u003c/li\u003e\n\u003cli\u003eMechanick JI, Apovian C, Brethauer S, et al. Clinical practice guidelines for the perioperative nutrition, metabolic, and nonsurgical support of patients undergoing bariatric procedures: 2019 update. Surg Obes Relat Dis. 2020;16:175\u0026ndash;247. doi:10.1016/j.soard.2019.10.025.\u003c/li\u003e\n\u003cli\u003eMocanu V, Marcil G, Dang JT, Birch DW, Switzer NJ, Karmali S. Preoperative weight loss is linked to improved mortality and leaks following elective bariatric surgery: an analysis of 548597 patients from 2015\u0026ndash;2018. Surg Obes Relat Dis. 2021;17:1846\u0026ndash;1853. doi:10.1016/j.soard.2021.06.021.\u003c/li\u003e\n\u003cli\u003eSun Y, Liu B, Smith JK, et al. Association of preoperative body weight and weight loss with risk of death after bariatric surgery. JAMA Netw Open. 2020;3:e204803. doi:10.1001/jamanetworkopen.2020.4803.\u003c/li\u003e\n\u003cli\u003eCassie S, Menezes C, Birch DW, Shi X, Karmali S. Effect of preoperative weight loss in bariatric surgical patients: a systematic review. Surg Obes Relat Dis. 2011;7:760\u0026ndash;767. doi:10.1016/j.soard.2011.08.011.\u003c/li\u003e\n\u003cli\u003eEsquivel MM, Azagury D. Preoperative weight loss before bariatric surgery: the debate continues. JAMA Netw Open. 2020;3:e204994. doi:10.1001/jamanetworkopen.2020.4994.\u003c/li\u003e\n\u003cli\u003eEng V, Garcia L, Khoury H, et al. Preoperative weight loss: is waiting longer before bariatric surgery more effective? Surg Obes Relat Dis. 2019;15:951\u0026ndash;957. doi:10.1016/j.soard.2019.03.012.\u003c/li\u003e\n\u003cli\u003evan Nieuwenhove Y, Dambrauskas Z, Campillo-Soto A, et al. Preoperative very low-calorie diet and operative outcome after laparoscopic gastric bypass: a randomized multicenter study. Arch Surg. 2011;146:1300\u0026ndash;1305. doi:10.1001/archsurg.2011.273.\u003c/li\u003e\n\u003cli\u003eAmerican College of Surgeons. User guide for the 2023 Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program Participant Use Data File (PUF). Version 2. Chicago (IL): American College of Surgeons; 2024.\u003c/li\u003e\n\u003cli\u003eGrieco A, Huffman KM, Cohen ME, Hall BL, Morton JM, Ko CY. The Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program bariatric surgical risk/benefit calculator: 30-day risk. Surg Obes Relat Dis. 2021;17:1117\u0026ndash;1124. doi:10.1016/j.soard.2021.02.005.\u003c/li\u003e\n\u003cli\u003eAmerican College of Surgeons. MBSAQIP 2022 variables and definitions. Chicago (IL): American College of Surgeons; 2022.\u003c/li\u003e\n\u003cli\u003eSaleh OS, Farag YMK, Medhati P, Tavakkoli A. Impact of preoperative weight loss on 30-day complication rate after bariatric surgery. J Am Coll Surg. 2024;238:993\u0026ndash;999. doi:10.1097/XCS.0000000000001036.\u003c/li\u003e\n\u003cli\u003eBlokhin IO, Lentz SR. Mechanisms of thrombosis in obesity. Curr Opin Hematol. 2013;20:437\u0026ndash;444. doi:10.1097/MOH.0b013e3283634443.\u003c/li\u003e\n\u003cli\u003eSamad F, Ruf W. Inflammation, obesity, and thrombosis. Blood. 2013;122:3415\u0026ndash;3422. doi:10.1182/blood-2013-05-427708.\u003c/li\u003e\n\u003cli\u003eBirkmeyer NJO, Finks JF, Carlin AM, et al. Risk factors for venous thromboembolism after bariatric surgery. Ann Surg. 2012;255:1100\u0026ndash;1104. doi:10.1097/SLA.0b013e31824c04d0.\u003c/li\u003e\n\u003cli\u003eHarrington LB, Benz L, Haneuse S, et al. Bariatric surgery and the long-term risk of venous thromboembolism: a population-based cohort study. Obes Surg. 2024;34:2017\u0026ndash;2025. doi:10.1007/s11695-024-07236-y.\u003c/li\u003e\n\u003cli\u003eBenotti PN, Still CD, Wood GC, et al. Preoperative weight loss before bariatric surgery. Arch Surg. 2009;144:1150\u0026ndash;1155. doi:10.1001/archsurg.2009.209.\u003c/li\u003e\n\u003cli\u003eStenberg E, Laurenius A, Thorell A. Intentional weight reduction before surgery: a systematic review. Clin Nutr. 2025;45:156\u0026ndash;164. doi:10.1016/j.clnu.2025.01.008.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Bariatric surgery, Preoperative weight loss, MBSAQIP, Serious complications, Venous thromboembolism, Sleeve gastrectomy, Roux-en-Y gastric bypass","lastPublishedDoi":"10.21203/rs.3.rs-8863406/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8863406/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003ePreoperative weight loss is commonly encouraged before bariatric surgery, yet its impact on short-term postoperative outcomes in contemporary practice remains uncertain. We evaluated the association between preoperative weight loss and 30-day postoperative outcomes using recent national registry data.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eWe conducted a retrospective cohort study using the 2020\u0026ndash;2023 Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) Participant Use File. Patients with body mass index\u0026thinsp;\u0026ge;\u0026thinsp;35 kg/m\u0026sup2; undergoing minimally invasive sleeve gastrectomy or Roux-en-Y gastric bypass were included. Preoperative weight loss was defined as a\u0026thinsp;\u0026ge;\u0026thinsp;2.0 kg reduction comparing the highest recorded weight within one year before surgery to the weight closest to the operative date, reflecting meaningful change beyond routine registry measurement variability. The primary outcome was 30-day serious postoperative complications, defined using the MBSAQIP bariatric surgical risk/benefit calculator composite. Multivariable logistic regression with robust standard errors was used. Prespecified sensitivity analyses included procedure-specific models, exclusion of robotic-assisted cases, and complete-case analysis for venous thromboembolism prophylaxis.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eAmong 621,849 patients, 68.2% experienced preoperative weight loss. Preoperative weight loss was associated with lower adjusted odds of serious postoperative complications (adjusted OR 0.96, 95% CI 0.92\u0026ndash;0.99). Weight loss was also associated with reduced venous thromboembolism (OR 0.88, 95% CI 0.78\u0026ndash;0.98) and shorter postoperative length of stay (negative binomial incidence rate ratio 0.98, 95% CI 0.98\u0026ndash;0.99). Findings were consistent across sensitivity analyses.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eIn a large contemporary national cohort, preoperative weight loss was associated with a statistically significant but modest reduction in serious postoperative complications and venous thromboembolism after bariatric surgery. These findings suggest that preoperative weight loss is associated with a modest incremental reduction in short-term postoperative risk but should not be used as the sole universal requirement for access to surgery.\u003c/p\u003e\u003ch2\u003eTrial registration\u003c/h2\u003e \u003cp\u003eNot applicable.\u003c/p\u003e","manuscriptTitle":"Association of Modest Preoperative Weight Loss and 30-Day Outcomes After Bariatric Surgery: A Contemporary MBSAQIP Analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-10 16:49:47","doi":"10.21203/rs.3.rs-8863406/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"936cbc34-47b1-4ed9-8f5d-1a9acb5216fc","owner":[],"postedDate":"March 10th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-27T18:10:14+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-10 16:49:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8863406","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8863406","identity":"rs-8863406","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}