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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 as NCT01174875.

Original publication




Journal article


Am J Clin Nutr

Publication Date





398 - 405


breastfeeding, formula feeding, gender, growth, infant, interaction, Body Height, Bottle Feeding, Breast Feeding, Child Development, Cohort Studies, Female, Growth Charts, Humans, Infant Formula, Infant Nutritional Physiological Phenomena, Infant, Newborn, Longitudinal Studies, Male, Mothers, Sex Characteristics, Singapore, Weight Gain