Nutrition in infancy - Clinical studies on dietary intake, metabolism and growth

Sammanfattning: Nutrition in infancy - Clinical studies on dietary intake, metabolism and growth Our aims were to try to determine an appropriate formula protein concentration to be used during the second half of infancy and to evaluate the effects on plasma lipids when breast milk was exchanged for formula and/or weaning foods. Both aspects were studied with special regard to the influence of traditional weaning foods. Nutrient intake, protein and fat metabolism, and growth were studied from 3 to 12 months in Swedish and Italian infants. Breast milk was gradually exchanged for formula with the same fat but different protein concentrations (13, 15 or 18/20 g/l) and given together with Swedish or Mediterranean weaning foods. Swedish infants given the lowest protein (13 g/l) formula had lower total dietary intake of protein and indices of protein metabolism more similar to those of breast-fed infants in mid-infancy compared with infants assigned to higher protein (15-18 g/l) formulas. Sufficient amounts of protein was provided to Swedish and Italian infants, since serum proteins and growth were normal in both populations. However, plasma concentrations of some essential amino acids were lower in Italian infants fed low-protein formula, despite higher protein intake. This may indicate that dietary protein from Italian weaning foods was less available in mid-infancy compared with protein from Swedish weaning foods. Dietary intake of protein was found to be associated with plasma levels of insulin-releasing amino acids, with renal excretion of C-peptide from insulin synthesis and also with growth. High dietary supply of protein may probably increase growth by promoting insulin release during infancy. Swedish breast-fed infants had higher plasma cholesterol than those fed formula, possibly since breast milk provides much saturated fat, more cholesterol and less unsaturated fat than formula. These differences decreased during the second half of infancy, when more weaning foods were provided. Moreover, residual effects of breast milk on the plasma lipid profile were lost soon after the termination of breast-feeding. Plasma lipids were lower in Italian infants at 6 and 12 months of age, partly since Italian weaning foods – and possibly also breast milk – differed in lipid composition from Swedish ones. Higher protein and lower fat and energy contents of Italian compared with Swedish weaning foods, may explain why Italian infants were given excessive protein but less fat and energy in late infancy. In conclusion, protein needs during mid- and late infancy seem to be better met by lower (13 g/l) than by higher (18 g/l) protein-containing formula when combined with high-quality weaning foods. Plasma lipids respond to changes in dietary intake from breast milk to formula and weaning foods, and differ between the Swedish and Italian infant populations in mid- and late infancy, which may partly be due to differences in fat composition of their weaning foods.