Macronutrient content of a hypoenergy diet affects nitrogen retention and muscle function in weight lifters

Weight lifters (WL) attempt to achieve a low body fat while maintaining fat free mass (FFM) and muscle function. Body composition and isometric muscular endurance were tested in 19 experienced male WL at the end of a weight maintenance and exercise routine standardization week. The subjects were assigned to either a control (C), moderate-protein (0.8 g.kg-1.d-1), high-carbohydrate hypoenergy diet (MP/HC), or high-protein (1.6 g.kg-1.d-1), moderate-carbohydrate hypoenergy diet (HP/MC). Both hypoenergy diets provided 75.3 kJ (18 kcal).kg-1.d-1. Apparent nitrogen balance (NBAL) was assessed using nitrogen in the diet, urine, and sweat. Body fat and FFM loss via hydrostatic weighing were not different between the hypoenergy groups. However, lean body mass (LBM) change as assessed by NBAL showed that the MP/HC group had an average negative NBAL of -3.19 g.d-1 while the HP/MC group had a positive NBAL of 4.13 g.d-1. Macronutrient mix did not affect biceps endurance, but quadriceps endurance declined for the HP/MC group during the experimental week. In conclusion, a hypoenergy diet providing twice the RDA for protein was more effective in retaining body protein in WL than a diet with higher carbohydrate but the RDA for protein. However, the lower carbohydrate of this diet contributed to reduced muscular endurance in these athletes.