Abdominal Adiposity and Muscle Mitochondrial Functions

Sixty 35 to 50-years old sedentary men will be included based on their abdominal circumference (from 75 to over 102 cm). Body composition will be evaluated using dual-energy X-ray absorptiometry and perivisceral, intramuscular and intrahepatic adiposity will be assess by MRI and proton-NMR spectroscopy. Subjects will be also characterized by their glucose tolerance (OGTT), basal metabolism (indirect calorimetry) and maximal oxygen consumption (maximal aerobic power test on exercise bike). Blood samples will be collected in the fasted state to assess lipids and adipokines concentrations. Biopsies will be obtained from the vastus lateralis muscle to examine mitochondrial functions (respiration rates, ATP and superoxide anion production rates, maximal activity of oxidative enzyme). Gene expression of key enzymes, protein and transcription factors involved in lipid and energy metabolism will be assessed using real-time quantitative PCR. Finally, whole body and muscle protein metabolism will be investigated in half of the subjects using tracer infusion (incorporation of L-\[1-13C\]leucine) and biopsies from vastus lateralis, both in the post-absorptive and post-prandial states (test meal)