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

Background: Studies indicate that maternal weight status modulates human milk composition; however, results are conflicting. Objectives: 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. Methods: Human milk samples were obtained from a longitudinal study (NCT 01131117) in normal weight (NW: 18.5-24.9 kg/m(2), n = 88) and overweight/obese (OW: 25-35 kg/m(2), 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 electrochemiluminescence immunoassays. Infant body composition was obtained using quantitative MRI. Linear mixed models were adjusted for postpartum age and infant sex. Results: 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). Conclusions: 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. This trial was registered at clinicaltrials.gov as NCT01131117.