Macronutrient and energy contents of human milk fractions during the first six months of lactation

To study the macronutrient and energy contents of human milk fractions during the first 6 mo of lactation. A total of 483 milk samples, including 52 pairs of fore- and hindmilk samples from 20 mothers, 253 samples from 53 donor mothers and 126 samples from 36 mothers of preterm infants, were collected longitudinally, starting at 1 wk postpartum and continuing monthly up to 6 mo. Protein, lactose and fat contents were measured and energy density estimated. The protein content was significantly lower in fore- and hindmilk than in donor or preterm milk during the first months of lactation. In donor and preterm milk, the protein content declined consistently from 2.0 g/100 ml at 1 wk to half of that at 6 mo, and a similar trend was observed in fore- and hindmilk. Lactose content showed no significant changes between the groups or in the course of lactation. The fat content was highest in hindmilk, being approximately two- to threefold that of foremilk. Accordingly, hindmilk included 25-35 kcal/100 ml more energy on average than foremilk. The fat content of human milk increases in relation to breast emptying, while the other macronutritients of milk show only slight changes. When enteral feeding with high-energy human milk is preferred, as in the case of very preterm infants, hind milk, with its higher fat content, would be a natural choice.