Free amino acid, protein, and fat contents of breast milk from Guatemalan mothers consuming a corn-based diet.

Diet compositions and breast milk levels of free amino acids, protein, and lipid were compared in lactating American and Guatemalan women. The protein in the American diet derived principally from animal sources, whereas that in the Guatemalan diet was based most exclusively on cereal grains and legumes. Corn, in the form of cornmeal, was the predominant food. Because of these dietary differences, the Guatemalan women consumed significantly smaller amounts of protein than the American women. The concentrations of most of the free amino acids in aliquots of breast milk from the Guatemalan women were lower than those in samples from the American women. In particular, tryptophan and lysine levels were 23% and 29%, respectively, of the levels in the American breast milk samples. The Guatemalan samples contained less protein, and, when values from Guatemalan women who had nursed only for 6 mth or less were considered, the fat content was also less than in the American samples. The lipid content of the milk, however, did not differ between the two groups when the length of the lactation period was not controlled. The substantial cultural differences between the two groups in the frequency and duration of nursing probably prevented the identification of a clear dietary influence on milk lipid content. The correlations found between diet composition and either the amount of protein or the levels of free amino acids in breast milk suggest that, if a mother's diet is deficient in high-quality protein, the deficiency may be reflected in the composition of her milk, perhaps to the detriment of the nursing infant.