{"paper_id":"8bb39900-53c9-4e24-9180-bae8d9befc75","body_text":"Endometriosis is one of the most common hormonedependent\ngynaecological diseases. It is a chronic inflammatory\ngynaecological condition that is characterized by\ndyspareunia, pelvic pain, and infertility ( 1 ). Despite the\nhigh association with morbidity, the prevalence, incidence,\naetiology and risk factors of endometriosis remain elusive\n( 2 ). Endometriosis may be related to genetic, hormonal,\nanatomic, immune, inflammatory, environmental and lifestyle\nfactors ( 3 ). The role of diet in several chronic diseases\nhas been determined ( 4 ). Oestrogen activity is a common\ndenominator for many known endometriosis risk factors\nand an association has been demonstrated between diet and\noestrogen dependency; therefore, endometriosis may also\nbe affected by diet ( 1 ,  5 ). The role of diet in the incidence\nand progression of endometriosis has become a growing\nfield of interest in recent years ( 6 ,  7 ) and summarized in\na recent review ( 8 ). Diet may play a role in its etio-pathogenesis\n( 9 ), and can be influenced through multiple pathways\nthat include effects on oxidative stress, prostaglandin\n(PG) metabolism, smooth muscle contractility, inflammation,\nimmune function and estrogenic effects ( 10 ). Huang\net al. ( 11 ) reported that dietary factors altered serum sexhormone\nconcentrations and activity. A few human studies\nexplored the relationship between diet and endometriosis\nrisk, but had conflicting results ( 1 ,  2 ,  12 ). Parazzini et al.\n( 12 ) found no association between the consumption of milk,\ncheese, carrots, fish and whole grain foods and the risk of\nendometriosis; however, there was a significant association\nbetween the intake of green vegetables, fresh fruit, and red meat with endometriosis risk. Alternatively, Yamamoto et\nal. ( 7 ), in a large cohort study, reported a significant association\nbetween the consumption of red meat and the risk\nof endometriosis, while consumption of fish, poultry, and\neggs were unrelated to endometriosis risk. Another large\nUS cohort study revealed that total fat consumption was\nnot associated with the risk of endometriosis ( 2 ). Of note,\nmost published studies supported the association used animal\nmodels of endometriosis and extrapolated the results\nto humans ( 13 ). According to the limited number of studies\non this topic and inconsistencies between these prior\nstudy findings, the present analytic research was conducted\nto further investigate if the selected diet factors affect the\noccurrence of endometriosis in Iranian women.\n\nThis case-control study was carried out at two referral\ncentres, Royan Institute and Vali-Asr Reproductive Health\nResearch Centre (both in Tehran, Iran), between April 2015\nand March 2016. The Institutional Review Board and the\nMedical Ethics Committee of Tehran University of Medical\nSciences approved this study. All procedures performed\nin this study were in accordance with the Declaration of\nHelsinki and an informed consent was obtained from all\nindividual participants included in the study.\nThe control and case groups were from both centres. A\ntotal of 510 women who underwent diagnostic laparoscopy\nwere recruited for this study. The main indications for\nlaparoscopy were symptoms of endometriosis (dysmenorrhea,\ndyspareunia and pelvic pain), uterine abnormality, tuboperitoneal\ndisorder and unexplained factor in infertility.\nWomen (n=97) who had adhesions, leiomyomas, fibromas,\nand/or uterine abnormalities at laparoscopy were excluded\nfrom the study. Finally, we included 413 women who were\ndivided into two groups according to the laparoscopy findings\nof endometriosis (case group) or normal pelvis (control\ngroup). Following surgery, the stage of the disease was\ndefined according to the classification system of the revised\nAmerican Society for Reproductive Medicine (rASRM) as\nstage I (minimal), stage II (mild), stage III (moderate) and\nstage IV (severe) ( 14 ). Histologic confirmation was obtained\nin 79.6% of the women with endometriosis.\nThe required data were collected using a structured questionnaire for information on\ndemographic variables and reproductive characteristics. For each selected dietary item in\nthe Iranian diet, the participants were asked about their frequency of consumption per\nweek (i.e., 14 meals) in the year before the interview. The questionnaire was a structured\nquestionnaire similar to that reported by Parazzini et al. in their study ( 12 ) on diet\nhabit; specifically, the selected dietary items were green vegetables (0-6, 7-12≥13\nportions/ week), fresh fruits (≤6, 7-13≥14 portions/week), carrots (0, 1≥2 portions/week),\ngrain legumes (0, 1≥2 portions/ week), red meat (0-3, 4-6≥7 portions/week), fish (0, 1≥2\nportions/week), milk (0, 0.5-6≥7 portions/week), cheese (≤2,  3 -5≥6 portions/week), eggs\n(0, 1≥2 per week) and green tea (yes or no). The items of green vegetables and fruits\nincluded all types, specifically all of the main sources in the Iranian diet such as\nspinach/other greens, kale, green salads, broccoli, cauliflower, citrus fruit, apples,\npeaches, melons, strawberries/cherries, bananas and pears.\nIn terms of content validity, we requested that 10 experts\nin the fields of nutrition, midwifery, reproductive\nhealth and gynaecology review the questionnaire and assess\neach item based on four criteria: relevancy, clarity,\nsimplicity, and necessity. The content validity ratio (CVR)\nwas calculated based on the responses to the necessity of\nquestions (nE) according to the following formula.\nCVR= (nE-N/2)/ (N/2)\nLawshe’s table was used to determine the CVR cut-off\npoint ( 15 ). According to Lawshe, for 10 professionals, the\nminimum required CVR for each item is 0.94. The content\nvalidity index (CVI) for this questionnaire was based\non the Waltz and Bausell CVI ( 16 ). The CVI for each item\nwas obtained by dividing the number of professionals who\nranked the items as compatible or full compatible for each\ncriterion (relevancy, clarity, simplicity, and necessity) to the\ntotal number of professionals. The average value of the three\ncriteria was used as the total CVI for each item. The minimal\nrequired amount of CVI for each item was 0.90 ( 17 ). A testretest\nanalysis with an interval of 15 days was approved in\na pilot study of 30 women with endometriosis. We assessed\nthe test-retest reliability of the questionnaire by using two\ncorrelational measures, Spearman’s correlation and Cohen’s\nkappa, to show the similarity in the responses to an item on\ntest and retest ( 18 ). According to Field ( 18 ) and Cade et al.\n( 19 ) large correlation coefficients of 0.5 or greater indicate\nhigh reliability. The value of Kappa identifies the strength\nof the agreement according to the categories reported by\nMasson et al. ( 20 ) of poor (<0.20), fair (0.21-0.40), moderate\n(0.41-0.60), good (0.61-0.80), and very good (0.81-1.00).\nTable 1 shows that all correlation coefficients are above 0.6,\nwhich indicates good reliability.\nSpearman’s r and Cohen’s kappa correlational measures between\ntest and retest\na ; Mode in test and retest is reported,  b ; Because this is a nominal\nvariable, and Cramer's V correlation coefficient was used.\nThe sample size was calculated according to the studied variables and based on the “rule of thumb” method. We considered at least 10 samples per variable; therefore, the sample size was estimated to be 200 women ( 21 ). The chi square or t-tests, when appropriate, were employed using SPSS software (version 22, USA) to compare categorical and continuous variables, respectively. We used logistic regression to determine the risk factors associated with endometriosis. In addition, logistic regression was used to adjust for age, education levels and body mass index (BMI). The odds ratio (OR) and 95% confidence interval (CI) were outputted for each of the calculated factors. In order to test the linear trend for ordinal variables such as green vegetables, fresh fruits, carrots, grains legumes, fish, eggs, meat, milk and cheese, we reported the OR and P value for the trend using category medians. P values less than 0.05 were considered to be statistically significant.\n\nThe distribution of cases and controls according to age and selected characteristics is presented in Table 2. The severity of disease was staged according to the rASRM classification of endometriosis. Endometriosis was staged as minimal (rASRM stage I) in 56 (27.1%), mild (rASRM stage II) in 24 (11.6%), moderate (rASRM stage III) in 44 (21.3%), and severe (rASRM stage IV) in 83 (40.1%). When the demographic characteristics of the women with endometriosis were compared with the control group, there were no significant differences detected in the age at menarche, parity, occupation, cigarette smoking and history of infertility. In contrast, there was a significant difference concerning age, education and BMI between the two groups. The mean age was 31.50 ± 5.52 years in the endometriosis group and 30.30 ± 5.96 years in the control group (P=0.02).\nComparison of demographic characteristics of endometriosis cases and controls.\n*  Chi square test, BMI: Body mass index, and Y; Year.\nTable 3 shows the relationship between selected food\nintake and the risk of endometriosis. Our results indicated\nthat intake of green vegetables (Ptrend=0.004) and red meat\n(Ptrend=0.015) were significantly associated with a lower\nrisk for endometriosis. Fresh fruits (Ptrend=0.015), dairy\n(milk [Ptrend=0.014] and cheese [Ptrend<0.001]), and grain\nlegumes (Ptrend<0.001) were associated with a decreased\nrisk for endometriosis. Table 3 shows an OR greater than\none for those with zero or one portion of grain legumes per\nweek compared to those with two portions of grain legumes\nper week. Decreased grain legume intake appears to be a\nrisk factor whereas higher grain legume intake appears to be\nprotective. Consumption of carrots, green tea, fish, eggs, and\noil were not significantly related to the risk for endometriosis.\nRisk of endometriosis and selected food intake\n† ; Reference category,  * ; P values are adjusted for age, education\nlevels and body mass index (BMI),  ** ; Determined using category medians,\n a  OR; Odds ratio, and CI; Confidence interval.\n\nThe findings of the present study indicate that higher intake of green vegetables (OR=0.39, 95% CI=0.21–0.74; Ptrend=0.004) and fresh fruits (OR=0.68, 95% CI=0.50–0.93; Ptrend=0.015) can lower the risk of endometriosis. In three investigations, the relationship between servings per week or day of fresh fruit and green vegetable intake and endometriosis risk were evaluated ( 15 ,  16 ,  27 ). Similar to our study, Parazzini et al. ( 12 ) reported that intake of fresh fruits and green vegetables decreased the endometriosis risk. In contrast, Trabert et al. ( 1 ) found that vegetable consumption was not related to risk of endometriosis; however, higher disease risk was associated with increased fruit intake. The study’s authors posited that the results could be associated with a higher percentage of pesticide consumption in the cultivation of fruit, which might produce reactive oxygen species and decrease the antioxidant capacity of fruits and vegetables. The use of organochlorine pesticides in fruits should not prohibit their use. Rather, the use of organic fruits or removing the peels from contaminated fruits should be considered ( 22 ). Harris et al. ( 23 ) prospectively assessed data collected from 70 835 premenopausal women and found that fruit intake was associated with a decreased endometriosis risk; among these, citrus fruits had strongest association and it was suggested that the presence of beta-cryptoxanthin in these foods was probably responsible for this phenomenon. Unlike our finding in green vegetables, they reported that consumption of some vegetables such as cruciferous vegetables, corn and peas or lima beans were related to a higher risk of endometriosis. This positive association was observed among women with no history of infertility, which might explain the inconsistency between our results and those reported by Harris et al. ( 23 ), given that the highly selected population (almost 90%) in our study consisted of infertile women.\nPopulations on vegetarian diets usually have elevated sex-hormone binding globulin (SHBG) levels ( 24 ). A low-fat diet also decreases the levels of oestrogen in both pre-menopausal and post-menopausal women ( 25 ). Oestrogen conjugates enter the hepatic circulation through the bile, and are interrupted by dietary fibre; this encourages faecal oestrogen elimination ( 26 ). Increased SHBG or reduced serum levels of oestrogen can decrease oestrogenic stimulation of the endometrium, and restrict the proliferation of tissues that produce PGs ( 12 ). Hormonal agents are a potential connection between endometriosis and diet, as unopposed oestrogens can increase endometriosis risk. More difficult to explain in biological terms is the protective effect of a fruit and green vegetable-rich diet. High levels of carotenoids, folic acid, vitamin C and lycopene in a diet rich in fruits and green vegetables may cause inhibition of cell proliferation ( 27 ). In addition, it seems that dietary fruits and green vegetables may be surrogates for fibre. Fibre, as mentioned previously ( 28 ), decreases enterohepatic circulation and may thereby decrease the risk or severity of endometriosis.\nThe findings in this study were inconsistent with the results of many similar studies in other countries ( 1 ,  7 ,  12 ,  13 ,  29 ). Our results showed a decreased endometriosis risk for those with 4-6 portions of meat per weak compared to those with 0-3 portions of meat per week (OR=0.61, 95% CI=0.41–0.91; Ptrend=0.015). Four studies analysed the risk of endometriosis with frequent red meat consumption ( 1 ,  12 ,  13 ,  29 ,  30 ), which is a rich source of saturated\nfat. In an Italian case–control study ( 12 ) and a prospective\ncohort study ( 7 ), high intake of red meat increased the\nrisk for endometriosis. In a Belgian matched case-control\nstudy with prospective recruitment, meat consumption\nwas not linked with the risk of peritoneal endometriosis\n( 29 ). In another case-control study ( 1 ), no association was\nfound between the risk of endometriosis and increased\nservings of red meat. The effect of red meat consumption\nreported by Parazzini et al. ( 12 ) could be connected to\nthe fat content and type of fat in meat. Meat diet contains\nlarge amounts of fat, which can further increase oestrogen\nlevels ( 7 ), and is comparably higher in omega-6 fatty\nacids (FAs), which stimulates the production of proinflammatory\nPGs ( 31 ). Fung et al. ( 32 ) have reported that\na high intake of meat is associated with elevated serum\nconcentrations of oestrogen sulphate and oestradiol;\nconsequently, its consumption might directly contribute\nto increased levels of circulating steroid hormone ( 33 )\nand to the maintenance of the disease. This is an arguable\ntopic in spite of comparable serum levels of oestradiol in\nwomen with and without endometriosis ( 34 ), although the\nlikelihood of elevations in local oestrogen synthesis with\nincreased red meat consumption cannot be excluded ( 13 ).\nIn a most recent study, Yamamoto, et al. ( 7 ) demonstrated\nthat the effect of high intake of meat among endometriosis\nwomen with no report of infertility was partly related to the\nrelationship between heme iron intake and endometriosis,\nwith the mechanism of inflammation triggered by\noxidative stress which involved in pathophysiology of the\nendometriosis.\nThere are several possible explanations for the\ninconsistency between our results and those obtained\nby other studies. One of the reasons for this discrepancy\ncould be the kind of meat consumed in Iran and other\ncountries. Beef and lamb are the most widely consumed\nmeats in Iran, whereas in most other countries, pork is\none of the highly consumed meats. Dioxin contamination\nin food products and animal food in Italy that occurred\nduring the entire study is another factor that could impact\nthe study results. The method for cooking meat is one of\nthe most effective factors that varies in different nations\nand cultures ( 35 ). Another possible explanation for this\nmight be the different slaughter procedures for sheep and\ncalves in Iran (ritual cutting) and other countries (captive\nbolt stunning). Schulze et al. ( 36 ) explained that in ritual\ncutting, animals suffer much less pain and less stress\nhormones. Also, as the heart of animals killed by this\nway works much later, more blood and other materials,\nincluding hormones, will be removed from the animals\n( 36 ); this could possibly be corroborated by other studies\nin which indicated an association between heme iron\nintake and endometriosis risk ( 7 ) and also reported lower\nconcentrations of hemopexin, which is the major vehicle\nfor the transportation of heme iron ( 37 ).\nIn the present study, we found no association between\nthe consumption of fish and endometriosis risk. This\nfinding was consistent with the results of similar studies\nconducted by Parazzini et al. (Italy), Trabert et al.\n(Belgium) and Heilier et al. (USA) ( 1 ,  12 ,  29 ). Harel et\nal. ( 38 ) reported that fish consumption had the potential\nto reduce PGE2 and PGF2α concentrations and could be a\npossible risk-reducing factor for endometriosis.\nOur findings suggest that dairy product consumption was associated with a reduced risk of\nendometriosis. As higher intake of milk (OR=0.65, 95% CI=0.47–0.92; Ptrend=0.014) and\nintake of 3-5 portions of cheese (OR=0.53, 95% CI=0.37-0.76; Ptrend<0.001)] was\nassociated with a decreased risk of endometriosis. Few studies have examined the\nassociation between the intake of dairy foods and nutrients with risk of endometriosis. In\nthe first human study that evaluated intake of dairy, Parazzini et al. ( 12 ) reported no\nassociation between milk or cheese consumption and risk of endometriosis. Alternatively,\nTrabert et al. ( 1 ) found a non-significant inverse correlation between dairy intake and\nrisk of endometriosis. The results of a prospective cohort study revealed that high\nconsumption of dairy products, specifically yogurt and ice cream during adolescence, was\nassociated with a lower risk of endometriosis ( 6 ). It has been shown that serum and\nperitoneal fluid proinflammatory cytokine concentrations are elevated in women with\nendometriosis ( 8 ). Dairy products may be related to the endometriosis-associated\ninflammatory responses ( 8 ,  10 ). Zemel et al. ( 39 ) stated that a milk diet decreased\ninflammatory markers and oxidative stress, including interleukin-6 (IL-6) and tumour\nnecrosis factoralpha receptor 2 (TNF-α R2). Another hypothesis for this association is the\nability of calcium and vitamin D to down-regulate insulin-like growth factor-I (IGF-1),\nwhich plays a role in the growth-promoting process and up-regulation of transforming\ngrowth factor beta (TGF-β) acts as a negative autocrine growth factor ( 1 ).\nOur result shows an OR lower than one for those with ≥ 2\nportions (OR=0.59, 95% CI=0.47-0.77; Ptrend<0.001) of\ngrain legumes per week compared to the reference group.\nHigher grain legumes intake appears to be protective. An\nanalysis of the number of servings per week of grain did\nnot show any association with the risk of endometriosis\naccording to Trabert et al. ( 1 ). Similarly, no association was\nreported between the intake of grain and endometriosis\nrisk ( 12 ,  30 ). Refined cereals can influence glycaemic\nload (GL) and glycaemic index (GI). These variables\nare used to estimate the rate of carbohydrate absorption\nand subsequent insulin demand. When insulin binds to\nits receptor in the endometrium, it is able to induce the\ngrowth of endometrial stromal cells. Moreover, hyperinsulinaemia\nincreases the level of oestrogens through\nreducing the serum level of SHBG and increases the\nlevel of IGF-1 by lowering the serum level of insulin-like\ngrowth factor-binding protein 1 (IGFBP-1). Both IGF-1\nand oestrogens stimulate endometrial cell proliferation ( 31 ). Accordingly, cereal consumption could be correlated with endometriosis risk.\nOur data do not support an association between endometriosis risk and intake of any of the other nutrients or food groups evaluated in this study (e.g., carrots, green tea, oil, and eggs).\nIn the present results, oil intake was not associated with endometriosis risk (p-trend=0.32); this finding was similar to our previous study ( 30 ) performed on 156 infertile patients (p-trend=0.21). In the Italian case–control study, no association was found between oil consumption and risk of endometriosis ( 12 ).\nThis study has some limitations. An inevitable limitation is that case-control studies in nutritional epidemiology may be at a potential risk for recall bias. Information depends entirely on memory and there may be possible variations in recall bias for cases versus controls. Cases may associate their disease to their bad dietary habits and may over-report consumption of foods considered unhealthy. However, we believe that since the majority of women interviewed were probably unaware of the possible relationship between diet and endometriosis, the effect of recall bias was relatively low. As approximately 90% of our study population in both groups were infertile, this might limit the generalisability of results to all endometriosis women. Thus, our findings have implications for women with endometriosis from infertility clinic-based studies. Another weak point of our study was that we did not use the food frequency questionnaire (FFQ) due to the disadvantages of longer food lists and an additional respondent burden ( 40 ). The strong point of our study was the detailed availability of all records for the 413 participants. All of the participants completed the questionnaire.\n\nDespite the limitations, this research demonstrates that there is some association between intake of green vegetables, red meat, dairy products, cheese, fresh fruit and grain legumes with lower risk of endometriosis. These results highlight the necessity for appropriate extensive prospective evaluations to study these factors in fertile women with endometriosis to increase generalization of the findings.","source_license":"CC0","license_restricted":false}