Estimated Protein Requirements for Athletes

Group

Sedentary men and women Elite male endurance athletes Moderate-intensity endurance athletes1 Recreational endurance athletesb Football, power sports Resistance athletes (early training) Resistance athletes (steady state) Female athletes

Protein Intake (g/kg/day)

-15% lower than male athletes a Exercising approximately four to five times per week for 45 to 60 min. b Exercising four to five times per week for 30 min at <55% VO2peak.

Partially adapted from Tarnopolsky, M., Nutrition, 20, 662, 2004.

1.2 g/kg/day. Similar results were found in young males performing circuit training with both endurance and resistance exercise where even after a 40-day adaptation period protein requirements were ~1.4 g/kg/day.168

Modest-intensity resistance exercise programs can attenuate nitrogen loss at protein intakes close to the RDA for protein intake in older adults.145 This phenomenon has also been observed in young men training with a protein intake of ~0.8 g/kg/day.169 The ability to achieve NBAL (through increased nitrogen utilization efficiency) with modest resistance exercise may be indicative of accommodation and not adaptation because of the lower protein intake (~0.8 g/kg/day).145 Campbell and colleagues145 also found that whole-body protein synthesis in the group consuming protein at 0.8 g/kg/d was lower than for the group who consumed protein intakes of 1.6 g/kg/day. We performed an NBAL experiment in six well-trained bodybuilders (>2 years training experience) and six sedentary individuals and found that the protein requirement for the trained bodybuilders was only 12% greater than that for the sedentary controls.65 We also found that the bodybuilders in this study were habitually consuming protein intakes of ~2.7 g/kg/day.65 However, the error of the NBAL method was demonstrated in this study because if the positive NBAL on the high protein intake were extrapolated to net protein retention (assuming no change in breakdown), there would have been a 200 g/day increase in lean body mass each day. Some lay reports have used these data in support of the high protein intakes consumed by the bodybuilders. However, the magnitude of the positive NBAL cannot be directly extrapolated to an increase in lean mass for two reasons. First, there is an inherent error in the technique, which overestimates NBAL at high nitrogen intakes,147 and second, protein synthesis and breakdown change in parallel.13

We followed up on our observations with two studies to more accurately characterize the impact of resistance training on dietary protein needs. In the first we reasoned that the protein requirements would be highest during the early adaptation period to unaccustomed training, since most of the myofibrillar protein accretion occurs within the first several months following the initiation of a resistance exercise program. Therefore, we exposed 12 young males to 2 months of a supervised resistance exercise program (6 days per week, 2 h/day, 70 to 85% 1RM) and measured NBAL, muscle mass, muscle protein, and strength before and after a 1-month period, where they were randomized to receive protein at 1.44 and 2.6 g/kg/day. We calculated the estimated protein requirement during this period to be ~1.65 g/kg/day.98 Strength, muscle protein, and lean mass gains following training were not different between the two protein intakes.98 We went on to use the conceptual framework put forth by Young et al.147 and studied the protein kinetic response to graded protein intakes in young males who were performing weight training and high-intensity sprinting/power activities (e.g., football and rugby).53 In this study we randomly allocated six sedentary males and seven athletes to receive a diet supplying protein at each of three levels (recommended intake, ~0.86 g/kg/day; moderate, ~1.4 g/kg/day; and high, ~2.4 g/kg/day). We measured NBAL, whole-body protein synthesis, leucine oxidation, and protein breakdown.53 We calculated the estimated safe protein intake to be 0.89 g/kg/day for the sedentary group and 1.76 g/kg/day for the athletes.53 The whole-body protein synthesis was greater for the athletes than for the sedentary controls at all protein intakes. Furthermore, whole-body protein synthesis was lower at 0.86 g/kg/day than at 1.4 and 2.8 g/kg/day, and appeared to plateau at around 1.4 g/kg/day for the athletes. At protein intakes of 2.8 g/kg/day, leucine oxidation increased nearly twofold, which provided evidence that protein intake above the requirement is merely oxidized for energy.53

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