Abstract
Background/Objectives: Human milk (HM) meets the nutritional needs of term-born infants. However, it remains unclear whether HM macronutrient concentrations and intakes differ by infant sex. We investigated sex- and country-specific differences in HM macronutrient and energy concentrations among exclusively breastfeeding Danish and Australian mothers, and sex-specific differences in 24 h HM intake and intakes of HM macronutrients, energy, and energy ratio in Australian infants. Methods: In this cross-sectional, multicenter study, 77 Danish and 84 Australian mothers donated HM samples between 2.5 and 5.5 months postpartum. Mid-infrared spectroscopy analyzed macronutrient concentration in the Danish samples. The creamatocrit method analyzed fat and biochemical assays analyzed lactose and protein in the Australian samples. Milk intake was measured using the test-weighing method. We used linear mixed-effect models to investigate sex- and country-specific differences. Results: There were no sex-specific differences in macronutrient and energy concentrations within either Danish or Australian cohorts. In all 161 HM samples, we found no sex-specific differences in lactose and protein concentrations. The 24 h median protein intake in Australian infants was 7.82 g in males and 7.26 g in females, (p = 0.274). The protein:energy ratio intake was 0.06 and 0.07 in male and females, respectively (p = 0.154). We also found no significant sex-specific differences in 24 h HM intake or intakes of fat, lactose, or energy. Conclusions: These findings suggest that males and females have similar macronutrient requirements during infancy. However, this needs to be confirmed in larger studies measuring 24 h milk intake.