In a crossover study with 3 nursing mothers it was shown that the concentration and composition of human milk lipids and the concentration of lactose, but not that of protein, quickly respond to changes in the mother's diet. Triglycerides were high with low-fat/high-carbohydrate diets as compared to high-fat/low-carbohydrate diets. Lactose was affected reversibly. The intake of linoleic-acid-rich fats resulted in milk lipids with a respective high linoleic acid content. Milk cholesterol and phospholipid concentrations correlated positively with the respective triglyceride concentrations.