Effects of Fructose and Exercise on Hepatic Lipid Metabolism

8 healthy male volunteers will be studied each on 3 occasions, ie * after 4 days on a weight maintenance diet containing 5% simple sugars + low physical activity * after 4 days on a weight maintenance diet containing 30% fructose + low physical activity * after 4 days on a weight maintenance diet containing 30% fructose + high physical activity At the end of each of these 3 periods, fructose induced hepatic de novo lipogenesis (13C palmitate synthesis in response to ingestion of a 13C fructose load) and plasma VLDL-triglyceride kinetics (measured with a bolus of 2H-labeled glycerol) will be measured