Maternal BMI is positively associated with human milk fat: a systematic review and meta-regression analysis

BACKGROUND: Lack of robust estimates of human-milk nutrient composition and influential maternal factors, such as body composition, are barriers to informing nutrition policies and programs. OBJECTIVE: The objective was to understand the relation between maternal BMI and human-milk energy, fat, and/or total protein. METHODS: Four electronic databases (MEDLINE, Embase, CINAHL, and Web of Science) were searched. Outcomes assessed were human-milk energy (kcal/L), fat (g/L), and total protein (g/L) from mothers 1 to 6 mo postpartum. Studies with data on maternal BMI or weight and height that quantified human-milk energy, fat, or protein between 1 and 6 mo postpartum were eligible. Random-effects meta-regression weighted by the inverse of the study-level SE was completed for each of the 3 outcomes. The certainty of evidence for each outcome was assessed using the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach. RESULTS: A total of 11,373 titles and abstracts were identified, and after full-text screening, 69 articles of 66 studies were included. Meta-regression results showed a positive association between maternal BMI and human-milk fat (β: 0.56 g/L; 95% CI: 0.034, 1.1; P = 0.04; I(2) = 93.7%, n = 63 datapoints). There was no significant association between maternal BMI and human-milk energy (β: 3.9 kcal/L; 95% CI: −1.6, 9.5; P = 0.16, I(2) = 93.3%, n = 40 datapoints) or total protein (β: 0.13 g/L; 95% CI: −0.16, 0.41; P = 0.37, I(2) = 99.1%, n = 40 datapoints). The certainty of evidence for human-milk energy was low and the certainty of evidence for fat and total protein was very low. CONCLUSIONS: Meta-regression analysis of available literature suggested an association between maternal BMI and human-milk fat between 1 and 6 mo postpartum. Future studies are needed to confirm the relation between maternal BMI; variation in human-milk energy, fat, and protein content; and the implications for child growth and development. This review is registered with International Prospective Register of Systematic Reviews (PROSPERO 2018 CRD42018098808) at https://www.crd.york.ac.uk/prospero/.