Methionine supplementation of soya products: effects on nitrogen balance parameters

Soybean protein is one of the best quality foods available. Contribution of soy to human nutrition increases because of its overall positive nutritional profile, low cost, high protein and excellent functional properties. Addition of methionine to rat soybean diets improve biological value of soy protein. Few studies on methionine fortification of soya protein were carried in infants, but fortification of baby formulas with this amino acid is usually found. This study was carried out to demonstrate in malnourished children that the effect of methionine supplementation of soya milk and soy isolated protein, as well as to compare with their results to cows' milk. A total of 30 malnourished children, 1 to 3 years old, admitted to our metabolic unit and distributed in groups of 6 children were studied. They were fed experimental formulas with cows' milk, soya milk, soya milk plus methionine, soya isolated and soya isolated plus methionine. Nutrient compositions of formulas were calculated to be similar to mothers' milk. DL-methionine, 1.5 g per 100 g protein content was added to soya milk and soya isolated formulas. Two nitrogen balances, 3 days each, were carried out. Fecal and urinary nitrogen, serum proteins, creatinine and urea in serum and urine were followed during the study. Results showed differences of intake and retention of nitrogen between some of the groups, but there were no statistically significant differences on protein absorption in the groups. No differences were demonstrated in serum proteins, total nitrogen and other serum and urine parameters analyzed. Cows' milk fed children presented the highest nitrogen retention in both balance studies. The addition of methionine to the soya milk formula increased the nitrogen retention, not reaching the cows' milk levels and did not have the same effect when added to the isolate soy protein.