The Effect of Infant's Sex on Human Milk Macronutrients Content: An Observational Study

Sex differences in infant mortality and neonatal morbidity have been previously documented. Few studies, with conflicting results, have investigated the interaction between human milk (HM) macronutrients and energy content and infant sex. To test the null hypothesis that HM macronutrients content will not be affected by infant's sex. We compiled previously generated data on macronutrients content of colostrum samples and mature milk samples collected from lactating mothers of healthy term infants. Macronutrient content was measured using mid-infrared spectroscopy. A total of 324 milk samples were included in the analysis consisting of 189 colostrum and 135 mature milk samples. There were 92 female and 97 male infants in the colostrum group and 65 female and 70 male infants in the mature milk group. Maternal age, gestational age, mode of delivery and percentage of large for gestational age, small for gestational age, and appropriate for gestational age were similar between female and male groups at all stages of lactation. Birth weight in male infants was significantly higher than in female infants (3389.5 ± 444.6 versus 3229.2 ± 415 g, p = 0.016). There were no statistically significant differences in macronutrient contents between the female and male groups at all stages studied. Macronutrients and energy content in colostrum and mature milk collected from mothers of term infants were unaffected by the sex of their offspring.