PROTEIN-TURNOVER IN MALNUTRITION

All body proteins are subject to continous renewal; the term used for this process is protein turnover or protein flux. The life span of the individual. body proteins - measured in terms of their half lives - v aries between a few minutes and more than 158 days. The order of magni tude of the overall whole body protein turnover depends upon the input of nitrogen-containing substances whose nitrogen is not derived from proteins (e.g. amino acids) into the non-protein pool, as well as on t he extent of the whole body protein synthesis. The protein synthesis i n the cells and tissues of the body, however, does not only depend on the nutritional supply of amino acids, but also requires that sufficie nt energy is provided. The reduced absorption of protein, fat and carb ohydrates in malabsorption syndromes is thus accompanied by a decrease in body protein synthesis. The protein flux in malabsorption syndrome s is additionally burdened by the faecal loss of endogenous proteins a nd by the production of energy from amino acid degradation (gluconeoge nesis). Any longterm disturbance in protein, fat and carbohydrate abso rption may therefore cause a life-threatening depletion of the protein store and subsequent disturbances in immunological defence mechanisms . The correlation between protein/energy malabsorption and protein tur nover in infancy and childhood has as yet not been studied systematica lly. Studies on infants suffering from enteritis or short bowel syndro me - as conducted by our group, using N-15 yeast protein hydrolysate a nd N-15 glycine as tracer substances - have revealed the high efficacy of both MCT-oligopeptide formulas and total parenteral nutrition for the normalization of the whole body protein turnover.