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

Aim: To study the macronutrient and energy contents of human milk fractions during the first 6 mo of lactation.

Study Design: 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.

Results: 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.

Conclusions: 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.