Bodybuilding is a metabolically contradictory sport. Athletes attempt to maximize muscle size, which requires muscle tension, calories, carbs, and key amino acids such as leucine. They also try to minimize body fat, which requires a caloric deficit. Cells have well-developed systems for conserving energy and turning on pathways that build and repair tissue. Two fascinating studies, one from the University of Connecticut, Storrs and the other from the University of Texas Medical Branch in Galveston, showed how the system works in times of nutrient excess and scarcity.

In the first study, scientists fed subjects a leucine-rich essential amino acid-carbohydrate supplement, which stimulated the mTOR pathway (promotes protein synthesis) and suppressed the AMPK system (controls muscle cell energy levels). In the second study, scientists put people on a reduced-calorie diet (20 percent fewer calories) with a relatively high protein content (1.5 grams of protein per kilogram bodyweight). The low-calorie diet suppressed the mTOR pathway and protein synthesis. Adequate energy intake, carbohydrates and key amino acids are vital for building muscle tissue. Bodybuilders will sacrifice muscle tissue whenever they go on calorie-restricted diets to lose fat. (Journal of Physiology, 582: 813-823, 2007; Journal of Nutrition 140: 745-751, 2010)

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