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 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 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.