Infant growth and body composition from birth to 24-months: Are infants developing the same?

Abstract Background Given the importance of infancy for establishing growth trajectories, with later-life health consequences, we investigated longitudinal body composition among infants from six economically and ethnically diverse countries. Methods We recruited mother-infant dyads using the WHO Multicenter Growth Reference Study criteria. We measured fat-free mass (FFM) in 1176 (49% female) infants from birth to 6-mo-of-age (Australia, India, and South Africa; n = 468), 3 to 24-mo-of-age (Brazil, Pakistan, South Africa, and Sri Lanka; n = 925), and derived fat mass (FM), fat mass (FMI), and fat-free mass (FFMI) indices. Height-for-age (HAZ), weight-for-age (WAZ), and weight-for-length (WFLZ) z-scores were computed. Sex differences were assessed using a t-test, and country differences using a one-way analysis of variance. We further compared subsamples of children who tracked the median for HAZ (-0.25 > HAZ < + 0.25), and those who did not. Results HAZ tracked well between 0 and 6-mo, but less so between 3 and 24-mo. The stunting prevalence peaked at 10.3% for males and 7.8% for females, at 24-mo. By 24-mo, girls had greater FMI (10%) than boys. There were significant differences in FFM (South African and Sri Lankan males) and FM (South African females and Sri Lankan males) by 24-mo-of-age, between infants whose length tracked the WHO median and those that did not. Conclusion In a multi-country sample representing more ideal maternal conditions, body composition was heterogeneous, potentially due to ethnic, breastfeeding, and dietary-pattern differences. Tracking the median of the WHO standard reduced FFM heterogeneity but not FM, suggesting that other factors may influence adiposity.