Variation in Fat, Lactose and Protein in Human Milk Over 24 H and Throughout the First Year of Lactation

Br J Nutr. 2002 Jul;88(1):29-37. doi: 10.1079/BJNBJN2002579.


Fat in human milk is extremely variable and can represent up to 50 % of infant energy intake. To accurately determine milk composition and infant intake at 1 (n 17), 2 (n 17), 4 (n 17), 6 (n 15), 9 (n 6) and 12 (n 5) months of lactation, samples of fore- and hind-milk were collected from each breast at each feed over 24 h periods from an initial group of seventeen women. The content of fat in milk varied over 24 h, with a mean CV of 47.6 (se 2.1) % (n 76) and 46.7 (se 1.7) % (n 76) for left and right breasts respectively. The 24 h amounts of fat, lactose and protein in milk differed between women (P=0.0001), but were consistent between left and right breasts. Daily milk production differed between breasts (P=0.0001) and women (P=0.0001). Accordingly, amounts of fat (P=0.0008), lactose (P=0.0385) and protein (P=0.0173) delivered to the infant over 24 h also differed between breasts and women (P=0.0001). The energy content of milk and the amount of energy delivered to the infant over 24 h were the same between breasts, but differed between women (P=0.0001). The growth rate of a group of only six infants in the present study was not related to either the concentrations or amounts of fat, lactose, protein and energy in milk over the first 6 months of life. These results show the individuality of milk composition and suggest that only a rigorous sampling routine that takes into account all levels of variation will allow the accurate determination of infant intake of fat, lactose, protein and energy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Child Development / physiology
  • Female
  • Follow-Up Studies
  • Growth / physiology
  • Humans
  • Infant
  • Infant Nutritional Physiological Phenomena / physiology
  • Infant, Newborn
  • Lactation / physiology*
  • Lactose / analysis
  • Lactose / metabolism*
  • Lipid Metabolism*
  • Lipids / analysis
  • Milk Proteins / analysis
  • Milk Proteins / metabolism*
  • Milk, Human / chemistry
  • Milk, Human / metabolism*


  • Lipids
  • Milk Proteins
  • Lactose