PROTEIN SPARING DURING TREATMENT OF OBESITY - KETOGENIC VERSUS NONKETOGENIC VERY LOW CALORIE DIET

Although it is generally agreed that both ketogenic and nonketogenic very low calorie diets promote weight reduction, there is no consensus on a preference of one diet over the other in regard to protein sparing. In the present study, we compared the effects of isocaloric (600 kcal/d) and isonitrogenous (8 g nitrogen/d) ketogenic (low carbohydrate) and nonketogenic diets on parameters of protein and amino acid metabolism, in 16 morbidly obese women maintained on these diets for 4 weeks while confined to a metabolic ward. Cumulative urinary nitrogen excretion (g/4 wk) was significantly (P < .01) greater (248 ± 6 v 207 ± 12, mean ± SEM, n = 8), and cumulative nitrogen balance significantly (P < .02) more negative (-50.4 ± 4.4 v -18.8 ± 5.7), during treatment with the ketogenic than with the nonketogenic diet. Plasma leucine concentration (μmol/L) was significantly higher (P < .05) during treatment with the ketogenic than with the nonketogenic diet at day 14 (210 ± 17 v 150 ± 8), but not at day 28 (174 ± 9 v 148 ±8). Whole-body rates of leucine oxidation (mmol/h) were significantly higher (P < .05) during treatment with the ketogenic than with the nonketogenic diet at day 14 (1.29 ± 0.20 v 0.92 ±0.10) and at day 28 (1.00 ± 0.16 v 0.75 ± 0.10). Conversely, proteolysis, as measured by leucine turnover rate and urinary excretion of 3-methylhistidine, was not significantly different between the diets. We conclude that there is greater protein sparing by the nonketogenic than by the ketogenic very low calorie diet, and the mechanism appears to be greater protein synthesis. © 1992.