Composition of Breast Milk in Women with Obesity

Background/Objectives: Among US breastfeeding women, those with obesity have significantly increased breast milk fat and caloric content from foremilk to hindmilk, with a 4-fold increase in fat content from the first to last milk sample. In view of different dietary norms and nutritional standards, we sought to evaluate the relationship between maternal BMI with breast milk fat and calorie content in women from Brazil, a low-middle-income country. Methods: Women who delivered singleton-term neonates were recruited from the Ana Abrao Breastfeeding Center (AABC) and Human Milk Bank at the Federal University of Sao Paulo, Brazil. These women were then studied at 7-8 weeks postpartum. Women were grouped by BMI categories of nonobese (NonOB; BMI 18.5-29.9) and obese (OB; BMI ≥ 30). A breast pump was applied, and milk samples were obtained continuously in 10 mL aliquots from foremilk to hindmilk; samples were analyzed for macronutrients and lipids, and maternal blood was analyzed for serum lipids and glucose. Results: As compared to NonOB women, those with OB had significantly higher milk fat in the mid (4.9 ± 0.3 vs. 3.9 ± 0.2) and last hindmilk (6.6 ± 0.4 vs. 5.5 ± 0.3) samples, though not in the first foremilk sample, as compared to NonOB women. In both NonOB and OB subjects, milk caloric and fat content increased 1.5 to 2-fold from foremilk to hindmilk, with the average milk caloric value being 11% greater in OB women. Protein content was significantly increased in all three milk samples (first, middle, and last) in women with OB. Conclusions: Although the value of breastfeeding remains clear, these findings may have significant implications for infant nutrition and excessive infant weight gain in women with OB.