Effects of low energy diets on protein metabolism studies with [15N]glycine in obese patients

The effects of low energy diets on protein metabolism in terms of the metabolic pool, active protein pool, and active and inactive protein synthesis rates were studied using [15N]glycine in five obese patients (percentage of ideal body weight, 120-190%). For 10 days, the patients were given a control diet containing 2,000 kcal of energy and 80 g of protein. For the next 2 weeks, they were given Diet A with 1,100 kcal of energy and 70 g of protein, and for the last 2 weeks given Diet B with 1,100 kcal of energy and 50 g of protein. During the Diet A period, the active protein pool and the active and inactive protein synthesis rates were about the same as during the control diet period, although the metabolic pool tended to be slightly smaller than during the control diet period. During the Diet B period, the metabolic pool, active protein pool, and active protein synthesis rate were all significantly different from the values during the control diet period. The results suggest that protein metabolism in obese patients is not maintained with less than 70 g of protein daily when energy intake was restricted to 1,100 kcal/day.