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
Torun et al. showing that isometric exercise improved protein utilization. Hence, while resistance exercise did improve nitrogen balance, the results of Campbell and co-workers and Torun et al.127 may not be directly applicable to younger resistance training athletes who are trying to gain lean mass and stimulate hypertrophy. Nonetheless, support for the possibility that more intense resistance exercise can improve nitrogen economy can be seen in the results of Phillips et al., who showed that, in the fasted state, an isolated bout of resistance exercise resulted in increased muscle net protein balance, implying an improved intracellular reutilization of amino acids. Others have also observed that exercise per se vs. the creation of an energy deficit via diet, results in improved dietary protein retention. That the athletes studied by Tarnopolsky et al.7,8 were all highly trained at the time of study and were performing exercise that was more intense than that described in the studies that showed a reduction in protein requirements may be a reason for the discrepancy. It is of paramount importance to understand the concepts of adaptation and accommodation in regards to protein requirements, particularly where athletes are concerned. This contention is highlighted by studies that have shown that protein balance can be achieved in exercising persons at very low to moderate protein intakes (i.e., ~ 1 g protein• kg–1•d–1or less), albeit at rather modest levels of exercise. It has been emphasized that obtaining nitrogen balance, particularly in long term studies, may be less reflective of requirement but rather of mechanisms that result in an accommodated state.130 At issue is whether the accommodation, by bodybuilders athletes, to the lower protein intakes results in a reduced level of synthesis of some protein(s) that might eventually compromise performance; however, to substantiate such a proposition would be very difficult given the inherent problems in conducting long-term studies involving dietary control in athletes. Millward has detailed some of the reasons questions of protein requirements weight lifting and are hard to determine in an exercising population.A retrospective analysis of nitrogen balance data7,8,117,143 from persons (50 data points) who were in a steady state of training and performing structured rigorous training involving resistance exercise is shown in Figure 12.4. A regression line drawn through these data show that nitrogen balance isachieved at a protein intake almost 46% greater than the RDA/RNI/DRI (1.26g protein•kg–1•d–1; see Figure 12.4). Inclusion of a 95% confidence interval in the regression line to achieve zero balance yields a safe protein intake of 1.35 g protein•kg–1•d–1 (Figure 12.4) or almost 60% greater than the current RDA/RNI/DRI. There is no doubt that the data presented in Figure 12.4 represent data from a variety of studies from athletes completing resistance exercise at a variety of intensities, with a variety of levels of experience.
Assuredly, exercise intensity, duration, frequency and training status will impact on whether someone requires more protein. The data of Gontzea et al., shown in Figure 12.2, highlight the fact that unaccustomed exercise can induce a negative nitrogen balance, though transiently. Moreover, Lemon et al.117 showed that novice weightlifters required more dietary protein (1.4-1.5 g protein•kg–1•d–1) than do more experienced weightlifters (1.05 g protein•kg–1•d–1) as reported in an earlier study.8 In addition, when intense weightlifting is combined with training for sports with both power and aerobic bases (rugby and football) protein requirements have been reported to be as high as 1.76 g protein•kg–1•d–1.7 As discussed earlier, the underlying reason for a training-induced reduction in dietary protein requirements7,8,117 for strength-trained persons likely relates to the fact that it is early in a resistance training program when the largest gains in lean body mass and the greatest rates of muscle hypertrophy are seen.84 Hence, after the introductory phase of beginning a strength training program and initial gains in lean mass are made, it is hard to reconcile that resistance “trained” athletes would have markedly elevated protein requirements. Instead, experienced weightlifters and bodybuilders not using anabolic steroids might require protein to support a slight elevation in basal (i.e., beyond 48 h after their last workout) protein turnover. Cross-sectional data from Phillips et al. demonstrate support for the postulate that trained resistance athletes, whether male or female, have an elevated turnover of muscle proteins at rest (~ 24% elevation in FSR at rest in trained vs. untrained). These observations of a training induced elevation in FSR12 have recently been confirmed longitudinally following 8 weeks of training in previously untrained novices (S.M. Phillips, unpublished observations). Can a general recommendation for the dietary protein requirement for weightlifters, bodybuilders, or any athlete desiring to gain lean mass, whether uninitiated or experienced, be made? First, a theoretical calculation might demonstrate to those who believe that, no matter what is recommended for dietary protein requirement for those desiring to gain lean mass, dietary protein must be greater than 2 g protein•kg–1•d–1 and that supplemental protein is necessary to gain muscle mass or strength.8,116 Some data used in this calculation comes from the studies generated by animal scientists who have dedicated far more effort to determining the most cost-efficient (and hence protein content perspective) way of increasing lean mass gains in growing steers. If we take the theoretical example of a person who initially weighs 100 kg (220 lb) and in a given year gains 10 kg (22 lb) of muscle (it needs to be strongly emphasized that this gain is purely muscle and not just body mass), this represents a highly impressive gain of lean muscle mass and likely at the “outer limit” of possible gains in lean body mass, without anabolic steroids. The question is, how much extra protein (if any) would this individual have to consume?
1. 10kg muscle = 2.5kg protein (assuming 75% of muscle mass is water).
2. Then 2.5kg protein = 2500g in one year or 2500g/365d/100kg = 0.0685 g protein•kg–1•d–1that is gained.
3. Assuming that, based on some values calculated from growing steers, eight times as much protein needs to be consumed to lay down the same amount of mass (note, this mass gain is not all muscle in steers and so application of this value to humans represents an overestimate): 0.0685 • 8 = 0.55 g protein•kg–1•d–1.
4. Assuming that the RNI/RDA/DRI is sufficient to cover all other protein needs, 0.86 g protein•kg–1•d–1 + 0.55 g protein•kg–1•d–1 = 1.41 g protein•kg–1•d–1.
What this calculation does not take into account is that resistance exercise actually increases the efficiency of protein and amino acid utilization (i.e., net muscle protein balance is less negative), which would actually reduce the amount of protein required to gain the 10 kg of muscle. An increased efficiencyof protein utilization following intense resistance exercise has been shown acutely,11 chronically,12 and in nitrogen balance studies.27,143 Campbell et al. reported that 11 weeks of resistance training improved nitrogen balance by ~13mg N•kg–1•d–1 or ~82 mg protein•kg–1•d–1, which would reduce the estimated dietary protein requirement of 1.41 g protein•kg–1•d–1 to 1.33 g protein •kg–1•d–1. Put in practical terms, 1.33 g protein•kg–1•d–1 for someone who weighs 110 kg (242 lb) would be equivalent to four glasses (~1000 ml) of low fat milk, one can of tuna (~115g), a 6-oz skinless roast chicken breast (~170g), one cup of low fat yogurt (~245g) and four slices (184g) of whole-wheat bread. The same diet would provide only 6300 kJ, or ~1500 kcal and would provide 37% of one’s energy from protein; however, it serves to illustrate how easy it is to obtain sufficient quantities of high quality protein from normal dietary sources. For an athlete in training, this sort of daily consumption is relatively easy to achieve without the use of protein supplements. Moreover, the training-induced improvement in nitrogen balance reported by Campbell et al. occurred in a group of elderly persons who did not experience significant muscular hypertrophy, likely due to the moderate training stimulus they received despite 11 weeks of resistance training. Hence, it may be that, with more intense resistance exercise programs resulting eventually in significant fiber hypertrophy, the efficiency of nitrogen utilization may be even greater than that reported previously. While there is only weak evidence linking persistently high protein diets (Table 12.2) with adverse health consequences such as renal disease and poor bone health, Price et al.146 have shown that high protein diets, once initiated, should be maintained to preserve lean mass.
Essentially, what has been shown is that high protein diets, while they may result in high fed gains (i.e., stimulation of protein synthesis); there is a concomitant high fasting loss of protein (see Figure 12.5). These findings146,147 have implications for athletes who habitually consume high dietary protein intakes; they run the “risk” of losing lean body mass if they do not consistently follow this practice. The fasting loss of protein (i.e., lean body mass) arises due to the fact that urea cycle and amino acid oxidative enzymes adapt to higher protein intakes via an increase in activity;143 hence, when one consumes high protein liver and potentially muscle, amino acid oxidative capacity is increased and hence with greater protein intake an increasingly larger proportion of dietary protein is directed toward oxidation. This assertion is supported as can be seen in Figure 12.5, which is adapted from the data of Price et al.146 that shows greater fasting oxidative losses of amino acids concomitant with greater fed gains (protein synthesis) with increasing protein intakes. Accordingly, the pattern of consuming a large amount of dietary protein must be maintained because a significant time period must elapse before fasting losses are reduced (i.e., the time taken for urea cycle and amino acid oxidative enzymes to adapt), which would lead to significant lean body mass losses.