Human milk composition differs by maternal BMI in the first 9 months postpartum

Authors: SIMS, CLARK - Arkansas Children'S Nutrition Research Center (ACNC); LIPSMEYER, MELISSA - Edward Via College Of Osteopathic Medicine; TURNER, DONALD - Arkansas Children'S Nutrition Research Center (ACNC); ANDRES, ALINE - Arkansas Children'S Nutrition Research Center (ACNC)

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2020
Publication Date: 5/13/2020
Citation: Sims, C.R., Lipsmeyer, M.E., Turner, D.E., Andres, A. 2020. Human milk composition differs by maternal BMI in the first 9 months postpartum. American Journal of Clinical Nutrition. https://doi.org/10.1093/ajcn/nqaa098.
DOI: https://doi.org/10.1093/ajcn/nqaa098

Interpretive Summary: Studies have shown that the composition of human milk changes based on maternal weight. The purpose of this study was to examine changes in milk composition over time in normal weight and overweight/obese women and determine if any differences in milk composition and infant intake associate with infant growth from 2 weeks to 9 months of age. Using milk samples from women that were participants in the Glowing study at Arkansas Children's Nutrition Center, we measured fat, protein, carbohydrates, metabolic hormones (insulin and leptin), and markers of inflammation (C-reactive protein (CRP), interleukin (IL) -6, IL-8, and tumor necrosis factor-a (TNF-a)). Milk from OW mothers was higher in fat and protein, and lower in carbohydrate content at some time points compared to milk from NW mothers. Leptin and insulin contents were higher in milk from OW mothers at all time points, and CRP was higher at most time points compared to milk from NW mothers. There were no differences in the content of the other markers of inflammation between milk from NW and OW mothers. The results were similar for the daily intake of infants for these components. The differences in fat, protein, and carbohydrate intakes were correlated with small changes in infant growth measurements. However, the differences in leptin and insulin were more strongly associated with infant growth. The infants from OW mothers were exposed to 1.5 to 2.5 times as much human milk-derived leptin and insulin on a daily basis compared to infants from NW mothers. The findings from this study show that infants from OW mothers are exposed to higher amounts of leptin, insulin, and CRP than infants from NW mothers. However, it is unclear if these components of milk would survive digestion in the stomach and remain active, and it is unclear if the differences in content result in changes in infant growth.

Technical Abstract: Studies indicate that maternal weight status modulates human milk composition; however, results are conflicting. Our objective was to examine the relation between maternal body composition and human milk macronutrients and bioactive components and also their association with infant daily intakes and body composition. Human milk samples were obtained from a longitudinal study (NCT 01131117) in normal weight (NW: 18.5–24.9 kg/m2, n = 88) and overweight/obese (OW: 25–35 kg/m2, n = 86) women between 0.5 and 9 mo postpartum. Macronutrient content was estimated using mid-infrared spectroscopy. Leptin, insulin, and C-reactive protein (CRP) were measured using electrochemilumines-cence immunoassays. Infant body composition was obtained using quantitative MRI. Linear mixed models were adjusted for postpartum age and infant sex. Human milk in OW mothers was higher in fat and protein and lower in carbohydrate content at some time points compared with that in NW mothers. Human milk leptin, insulin, and CRP concentrations were higher in OW mothers compared with NW mothers, with infants of OW mothers exposed to 1.5–2.5 times higher concentrations of leptin and insulin compared with infants of NW mothers. Similar results were observed when concentrations were normalized to infant daily intake and body weight. The effect sizes of infant daily intakes associated with infant growth parameters were small for macronutrients [0.005–0.05 z-score units and 0.02–0.45 fat mass index (FMI) or fat-free mass index units per unit of change in composition, P < 0.05]. Larger effect sizes were seen with human milk insulin and leptin (0.24 z-score units and 0.37–1.15 FMI units per unit of change in composition, P < 0.05). These findings demonstrate that infants of OW mothers are exposed to higher concentrations of insulin, leptin, and, to a lesser extent, CRP. The bioavailability of these 3 human milk bioactives and their mechanisms of action in the infant are unclear.