Macronutrients
The macronutrient composition of human milk varies within mothers and across lactation
but is remarkably conserved across populations despite variations in maternal nutritional
status.13 As shown in Table 1, the mean macronutrient composition of mature, term milk is
estimated to be approximately 0.9 to 1.2 g/dL for protein, 3.2 to 3.6 g/dL for fat, and 6.7 to
7.8 g/dL for lactose. Energy estimates range from 65 to 70 kcal/dL, and are highly correlated
with the fat content of human milk. Macronutrient composition differs between preterm and
term milk, with preterm milk tending to be higher in protein and fat (Table 1).
A study in
Davis, California examined the association between maternal characteristics and the
composition of human milk macronutrients10 and found that after 4 months postpartum, the
macronutrient concentrations of human milk are associated with one or more of the
following factors: Maternal body weight for height, protein intake, parity, return of
menstruation, and nursing frequency. This study also found that mothers who produce
higher quantities of milk tend to have lower milk concentrations of fat and protein but higher
concentrations of lactose.
The proteins of human milk are divided into the whey and casein fractions or complexes,