Protein turnover in the elderly: a comparison between ill patients and normal controls

Total body protein turnover was measured in a group of ill geriatric patients and compared with healthy elderly controls. The subjects were fed a liquid formula and a tracer dose of [15N]-glycine by nasogastric tube. Total body nitrogen flux and hence protein synthesis and breakdown rates were calculated from the abundance of 15N in urinary ammonia. Urinary creatinine excretion and plasma albumin were also measured. The ill subjects had significantly higher total body nitrogen flux (P less than 0.025), protein synthesis (P less than 0.025) and breakdown rates (P less than 0.025) and significantly lower plasma albumin (P less than 0.01) and 9-h creatinine excretion (P less than 0.01) than the control group. This increase in protein turnover in spite of a reduced muscle mass in the ill subjects appears to be mainly due to the effects of tissue trauma and inflammation.