• The effect of a three-month period on a high-protein reducing diet on body composition was studied in 17 obese adolescents, aged 12.5 to 17.4 years. Body composition was assessed by estimating fat-free body mass from four skin-fold thicknesses, total body potassium by natural potassium 40 abundance, and total body nitrogen by prompt gamma ray analysis. Weight loss was 15% of initial body weight. Total body nitrogen loss was only 4.8% (not significant), while total body potassium fell by 13.2%. Change in fat-free body mass estimated from skin-fold thicknesses constituted approximately 44% of the total weight lost. There was no correlation between changes in total body potassium and total body nitrogen, suggesting that total body potassium cannot be used to predict total body nitrogen in a changing nutritional state.
(Am J Dis Child 1983;137:658-662)