Variation in the contents of nutrients of breast milk during one feeding

The concentrations of fat, lactose, total nitrogen, non-protein nitrogen, individual milk proteins (lactoferrin, α-lactalbumin, human serum albumin) and urea in breast milk were estimated in relation to the quantity of milk expressed from one breast on one occasion in 4 women. The water-soluble components were in most cases in similar concentrations throughout the feeding although exceptions were noted for individual proteins and urea. The fat concentration was low at the beginning and increased during emptying of the breast. The significance of the results in relation to adequate sampling of breast milk is discussed.