Human Milk Macronutrient and Energy Contents Are Associated with Maternal and Infant Factors: A Cross-Sectional Analysis of Data from the Japanese Human Milk Study Cohort.

Background: Human milk (HM) macronutrients are vital for infant growth and development; their composition may vary according to maternal and infant characteristics and differ across populations. However, the wide range of maternal and infant factors affecting HM macronutrient content among Japanese mothers has not been sufficiently evaluated. Objectives: We comprehensively examined the factors associated with the macronutrient content of mature HM in a cross-sectional analysis of a large Japanese cohort. Methods: A cross-sectional analysis was conducted using baseline data from the Japanese HM Study cohort (n = 1071). Macronutrient and energy contents were assessed in mature HM samples collected at an average of 2 mo postpartum. Maternal and infant factors were obtained via self-reported questionnaires. Linear regression analyses were performed to identify associations between these factors and HM macronutrient and energy contents. Results: Multivariable linear regression revealed significant associations between HM composition and several maternal and infant factors. True protein content was negatively associated with days postpartum [days; partial regression coefficient (B) = -0.0036, P < 0.001] and exclusive breastfeeding (B = -0.1045, P < 0.001). Carbohydrate content was positively associated with exclusive breastfeeding (B = 0.0963, P < 0.001). Fat content had a positive association with maternal overweight or obesity (B = 0.4648, P = 0.008) and negative associations with birth weight (g; B = -0.0002, P = 0.043) and days postpartum (days; B = -0.0103, P < 0.001). Crude protein and energy contents showed patterns similar to those of true protein and fat, respectively. Conclusions: For Japanese mothers, the macronutrient and energy contents of mature HM were associated with exclusive breastfeeding, maternal overweight or obesity, infant birth weight, and days postpartum.This trial was registered at https://center6.umin.ac.jp/cgi-open-bin/icdr_e/ctr_view.cgi?recptno=R000017649 as UMIN000015494.