[Free amino acids in plasma and milk of mexican rural lactating women]. / Aminoácidos libres en plasma y leche de mujeres lactantes rurales.

OBJECTIVE: To determine the free amino acid pool in plasma and milk in Mexican rural lactating women. METHODS: Twenty-eight women with an age 24 +/- 5.0 (+/- SD) years, weight 50 +/- 4.9 kg and height 148 +/- 4.8 cm were studied under metabolic balance conditions. Subjects were divided into five groups (three groups of lactation at 1st, 3rd and 6th month, one post-weaning group and a control group of non pregnant, non lactating women). Amino acid analyses of the diet and of plasma and milk samples were performed using an automated amino acid analyzer. RESULTS: Differences were observed between the lactation groups and the other groups: aspartate increased at the 6th month (p < 0.05) while leucine, valine and isoleucine declined in the 3rd month (p < 0.05). In milk, valine, proline and taurine decreased at 6 months (p < 0.05), while serine and threonine raised at 3 months. Plasma levels were > 4 fold greater than milk levels for branched chain amino acids and for the basic, aromatic and neutral amino acids. In contrast, glutamate was 40 fold higher in milk than plasma and it was the predominant amino acid in the free pool of milk. CONCLUSIONS: Our results suggest that the metabolic use of amino acids and the presence of specific amino acid transport systems during lactation, contribute to specific concentrations of free amino acids in milk that were not associated with the pool of free amino acids in plasma.

Significance of lipid consumption during lactation.

Human milk lipids are the main source of energy to support optimum growth of the breast-fed infant. The content and composition of milk lipids come from three main sources of fatty acids: the diet, mobilization of body fat stores and fatty acid synthesis de novo by the mammary gland. On account of these, the consumption and composition of the lipids from the diet and also the nutritional state, specifically the body fat percentage of the lactating woman, are elements that maintain a close relation with the content and composition of milk lipids which translates into the energy content given to the baby. The evidence suggests that the body fat stores significantly provide the demand imposed by lactation, and under suboptimal nutritional conditions where body fat stores are depleted, dietary lipid consumption is essential. It is necessary to elucidate the physiological regulatory mechanisms involved in the utilization of dietary lipids on milk synthesis. This information will be of great practical value, since it may allow the development of optimum diets for lactating women.