Protein Requirements for bodybuilding (resistance trained) athletes

Tarnopolsky and co-workers8 conducted a study using the nitrogen balance approach to examine the protein requirements of a group of bodybuilding -resistance trained athletes and a group of sedentary controls. As pointed out earlier, Tarnopolsky et al. have demonstrated that an isolated bout of resistance exercise did not increase leucine oxidation or perturb whole body protein turnover, likely because of the periodic recovery that occurs during a resistance vs. an endurance workout. Hence, it would appear that any extra protein required by strength-trained individuals is likely directed toward muscular hypertrophy in the earlier phases of training, when muscle mass is still increasing.

However, it should be stressed that, in highly trained powerlifters and bodybuilders, it is unlikely that dietary protein requirements are elevated much more than those of a sedentary person. In fact, any increase in protein requirements for such a highly trained group of individuals is likely only due to an increased rate of resting protein turnover. In support of the idea that training might induce an increase in resting muscle protein turnover, protein requirements of highly trained bodybuilders were found to be only 12% greater than those of sedentary controls, who had a protein requirement of 0.84 g protein•kg–1•d–1.8 The results of this study8 do highlight a puzzling result, however, that is evident in Figure 12.4. For example, on a protein intake (actually equivalent to the habitual protein requirement of bodybuilders) of ~2.8 g protein•kg–1•d–1, all bodybuilders were in highly positive nitrogen balance (~12-20 g N•d–1). When extrapolated back to actual protein, this would have meant that the bodybuilders should have gained ~ 300–500g of lean mass/d–1 (assuming muscle is 75% water and assuming that no other pool of body protein significantly increased in size), which obviously did not occur.8 The increasingly positive nitrogen balance, associated with higher protein intakes, that was observed in this8 and other7,117 studies is often incorrectly used to justify why high protein intakes are needed for resistance-trained athletes. Such shortcomings of nitrogen balance have long been recognized and have led to the recommendation of combining tracer and nitrogen balance approaches to determining protein requirements. Using a combination of nitrogen balance along with kinetic measurements of whole-body protein turnover, football and rugby players had protein requirements almost ~ 100% greater than those of a sedentary control group. In fact, onsumption of the low-protein diet (0.86 g protein•kg–1•d–1) by the strength trained group resulted in an accommodated state where whole body protein synthesis was reduced compared with the medium (1.4 g protein •kg–1•d–1) and high protein (2.4 g protein•kg–1•d–1) diets. In contrast to the results of Tarnopolsky et al., nitrogen balance studies conducted in the elderly have shown that initiating a moderate program of bodybuilding-strength training resulted in reduced protein requirements due to the anabolic stimulus of the resistance exercise. However, even following 10 weeks of comparatively mild resistance training, there was no evidence of muscle hypertrophy in people consuming either 0.8 or 1.6 g protein•kg–1•d–1. The results of Campbell et al. are remarkably similar to those reported by