Sexually dimorphic response to feeding mode in the growth of infants.

Background: The relation between infant feeding and growth has been extensively evaluated, but studies examining sex differences in the influence of infant milk feeding on growth are limited.
Objective: We examined the interaction of infant feeding and sex in relation to infant growth and compared growth trajectories in breastfed and formula-fed boys and girls.
Design: In 932 infants in a Singapore mother-offspring cohort, feeding practices in the first 6 mo were classified into the breastfeeding group (BF), mixed feeding group (MF), and formula feeding group (FF). Infant weight and length were measured and converted to WHO standards for weight-for-age z scores (WAZs) and length-for-age z scores (LAZs). Differences in WAZ and LAZ from birth to 6 mo, 6 to 12 mo, and 12 to 24 mo of age were calculated. Three-way interactions were examined between feeding mode, sex, and age intervals for WAZ and LAZ changes, with adjustment for confounders.
Results: The interaction between feeding mode, sex, and age intervals was significant for LAZ changes (P = 0.003) but not WAZ changes (P = 0.103) after adjustment for potential confounders. Compared with BF girls, BF boys showed similar LAZ gain (+0.28 compared with +0.39, P = 0.544) from 0 to 6 mo of age but greater LAZ gain from 6 to 12 mo of age (+0.39 compared with -0.10, P = 0.008). From 0 to 6 mo of age, FF boys and girls showed greater LAZ gains than their BF counterparts; from 6 to 12 mo of age, FF girls showed higher LAZ gain (+0.25 compared with -0.10, P = 0.031) than BF girls, which was not seen in boys.
Conclusions: During infancy, there is a sexually dimorphic growth response to the mode of infant milk feeding, raising questions about whether formula feeding ought to remain sex neutral. However, further investigations on sex-specific feeding and infant growth are warranted before a conclusive message can be drawn based on our current findings. This trial was registered at www.clinicaltrials.gov as NCT01174875.
(© 2016 American Society for Nutrition.)