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.

Objectives: This study aimed to determine the change in milk macronutrient and energy concentrations from ∼2 to 5 mo 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 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 mo) to visit 2 (∼5 mo), median milk protein concentration decreased from 1.4 g/dL [interquartile range (IQR): 1.1-1.6 g/dL] to 0.8 g/dL (IQR: 0.6-1.1 g/dL), median fat concentration decreased from 4.6 g/dL (IQR: 3.8-5.5 g/dL) to 2.8 g/dL (IQR: 2.1-3.7 g/dL), and median energy concentration decreased from 22.7 kcal/oz (IQR: 20.6, 25.1 kcal/oz) to 17.5 kcal/oz (IQR: 15.6-19.9 kcal/oz). Maternal overweight status was associated with a lower carbohydrate concentration (2 mo-mean difference: -0.16 g/dL; 95% CI: -0.28, -0.03 g/dL; 5 mo-mean difference: -0.14 g/dL; 95% CI: -0.26, -0.02; reference = 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.