Short-term Carbohydrate Restriction Increases Both Proteolysis And Protein Synthesis

Abstract

PURPOSE To assess the influence of a short-term weight-maintaining carbohydrate restricted diet on whole-body proteolysis and skeletal muscle protein synthesis. METHODS Eight subjects (4 women, 4 men) were studied after 2d of a standard diet (60% CHO, 30% fat, 10% protein) and after 2d and 7d of an isocaloric low-carbohydrate (LC) diet (5% CHO, 60% fat, 35% protein) during a 9d hospital stay. Whole-body proteolysis (leucine rate of appearance in plasma [Ra]) and skeletal muscle fractional synthetic rate (FSR) were measured using isotope tracer techniques after an overnight fast before (PRE), and after 2d and 7d of the LC diet. We also measured fat free mass (FFM), using DEXA, before and after the LC diet. RESULTS Leucine Ra was elevated (p < 0.05) 21 ± 2% and 15 ± 1% above PRE after 2d and 7d LC diet, respectively. Compared with PRE, muscle FSR was −2 fold higher (p < 0.05) after 7d of the LC diet (0.049 ± 0.004 v. 0.094 ± 0.013 %/h). However, FFM was not altered by the LC-diet. 24h insulin AUC was 50% lower (p < 0.05) after 2d and 7d LC diet while 24h growth hormone (GH) secretion and plasma insulin-like growth factor 1 (IGF-1) were unchanged with the LC diet. CONCLUSION Despite a lower 24h exposure to insulin and no change in GH or IGF-1 concentrations, whole-body protein breakdown and skeletal muscle protein synthetic rate were both increased in response to short-term isocaloric LC diet. Identical FFM before and after the diet suggests that the enhanced proteolysis during the dietary treatment was offset by a compensatory increase in FSR. This research funded by NIH#MO1RR042 (JFH).