Maternal and infant predictors of human milk macronutrient and energy concentrations in rural Bangladesh: an observational cohort study.

Background: Human milk macronutrient (protein, fat, and carbohydrate) and energy concentrations vary based on maternal and infant factors and time postpartum.

Objective: To determine the change in milk macronutrient and energy concentrations from approximately 2 to 5 months postpartum and identify factors associated with this variation among a lactation cohort in Bangladesh.

Methods: In this prospective observational lactation cohort in rural Sylhet, Bangladesh, we collected hand-expressed mid-feed human milk samples and analyzed macronutrient concentrations using mid-infrared spectroscopy. We used the Wilcoxon rank-sum test to compare macronutrient and energy concentrations between time points and mixed linear regression to determine associations between predictors (maternal body mass index [BMI], maternal mid-upper arm circumference, infant gestational age, and infant small-for-gestational age (SGA) status) and repeated measures of milk macronutrient and energy concentrations in models adjusted for parity, nicotine, and wealth index.

Results: We enrolled 99 participants. From visit 1 (∼2 mos) to visit 2 (∼5mos), median milk protein concentration decreased from 1.4 g/dL (IQR 1.1, 1.6) to 0.8 g/dL (IQR 0.6, 1.1), median fat concentration decreased from 4.6 g/dL (interquartile range [IQR] 3.8, 5.5) to 2.8 g/dL (IQR 2.1, 3.7) and median energy concentration decreased from 22.7 kcal/oz (IQR 20.6, 25.1) to 17.5 kcal/oz (IQR 15.6, 19.9). Maternal overweight status was associated with a lower carbohydrate concentration (2 months: mean difference [MD] -0.16 g/dL [95% confidence interval [CI] -0.28, -0.03]; 5 months: MD -0.14 g/dL [95% CI -0.26, -0.02]; ref = normal BMI).

Conclusions: The decline of protein, fat, and energy concentrations over time is a potential concern for Bangladesh's vulnerable population of human milk-fed infants, as these nutrients have implications for infant growth and neurodevelopment.