Interrelationships of glucose and protein metabolism in obese adolescents during short-term hypocaloric dietary therapy

We studied the interrelationship of nitrogen balance (N-bal) and rates of glucose appearance (Ra), determined isotopically using U-13C-glucose, in 14 obese adolescents consuming either (1.5 g protein and 1.0 g glucose)/kg ideal body weight/day or an isonitrogenous diet made isocaloric with fat. Nitrogen balance was significantly (p < .01) more positive with added glucose. Changes in plasma insulin, free fatty acids, or β-hydroxybutyrate did not reliably predict N-bal. The Ra of glucose decreased significantly on both diets, but was significantly lower (p < .001) after the addition of fat. A significant correlation of N-bal with Ra (r = 0.70, p < .01) was observed only in the absence of dietary glucose. Insulin levels correlated with N-bal only in the presence of dietary glucose (r = 0.72, p < .01). Nitrogen balance in the absence of dietary carbohydrate may be a consequence of net peripheral protein catabolism that is not directly mediated by the need for gluconeogenic precursors.