The Protein Needs Of Athletes

Recommended protein intakes for athletes has been a controversial topic for decades. Some research has indicated that the protein requirements for athletes is just slightly higher than it is for sedentary individuals (1,2,3), while the results of other studies have indicated that athletes may have significantly higher protein requirements (4,5,6,7). In 1980 the American Dietetic Association maintained the position that athletes did not require additional protein, because the recommended daily allowance (RDA) (0.8 g/kg body weight) for that macronutrient included a safety margin of two standard deviations (6).

Research indicates that athletes participating in several hours of aerobic exercise each week have protein requirements 50%-100% greater than the RDA of 0.8 g/kg body weight.

Meredith (2) and Tarnopolsky (3) suggested that athletes training at moderately high intensities for several hours per week experience an increased catabolism of protein, and thus have an increased daily requirement for that nutrient. The Meredith study included two age groups (26.8 + 1.2 yrs; 52.0 + 1.9 yrs), and the protein requirement of the groups was the same. The six young subjects in the Meredith study and the six subjects in the Tarnopolsky study were very similar in age and activity levels (aerobic exercise > 12 hrs/week).

There is less agreement between studies that have investigated the protein needs of athletes performing strength training activities. Differences in methodology may have contributed to the disparity in results.

Celejowa & Homa (5) and Laritcheva et al (6) suggested the protein needs of strength athletes were more than 200% the RDA. Tarnopolsky (3) argued that the lack of sweat collection (to measure urea nitrogen loss), diet adaptation periods between trials, distribution of accurately analyzed diets, and a control group made the conclusions of those studies questionable.

In the 1988 Tarnopolsky study (3), two of the six subjects were in negative protein balance (determined by urea nitrogen loss in urine, sweat, and fesces) when fed a diet that provided 1.0 g/kg body weight for protein. The authors suggested more subjects would have been in negative protein balance had the intensity of the training routine, which was not clearly described, been higher.

In 1992, Lemon et al (8) performed a tightly controlled study on a group of 14 bodybuilders. This double-blind study incorporated two 1-month treatments that supplied a diet consisting of 1.35 g/kg or 2.62 g protein/kg body weight. There was a seven day washout between trials, and the high intensity workouts of the subjects were supervised by trained personnel. Muscle biopsy, hydrostatic weighing, and CAT scans were used to assess anthropometric changes during the two phases of the study. There were no significant differences in strength and anthropometric measures between diet treatments, and the authors concluded, based on measures of nitrogen balance, that an ideal intake for protein was 1.6 g/kg – 1.7 g/kg body weight.

The results of work by Butterfield (9,10) and Roy et al (11) indicate that limiting factor for muscle protein deposition and maintaining a positive nitrogen balance is total caloric intake, not protein. Roy examined the effects of the timing of glucose supplementation on muscle protein synthesis. The subjects in that study performed unilateral leg extension exercise and received either a placebo or a carbohydrate supplement immediately after exercise and one hour post exercise. The fractional protein synthetic rate of the exercise limb in the carbohydrate group was 36 % higher than the control limb, and in the placebo group the exercise limb exhibited a 6.3 % higher synthetic rate than the control limb. Urinary urea nitrogen and 3-Methylhistidine excretion were also significantly lower in the carbohydrate supplement group.

Butterfield and Calloway (10) studied previously untrained men initiating moderate intensity exercise (40 % – 50 % VO 2 max) for one and two hours a day. Energy intake was altered in both exercise conditions to produce periods of energy balance and deficit. The authors found that when caloric intake was 15% higher than that needed to maintain body weight, nitrogen balance was achieved on a diet consisting of only 0.57 g of egg white protein per kg body weight. In a separate study, Butterfield (9) reported that male runners receiving a diet deficient in total energy but high in protein (2.0 g protein/kg body weight) while running 5-10 miles per day, were in negative nitrogen balance.

Research indicates that the protein needs of athletes can be as much as 100 % greater than the RDA of 0.8 g/kg of body weight. The 2000 position stand of the American Dietetic Association states that 1.5 g protein/kg body weight may be needed to achieve maximum protein deposition. However, total caloric intake may be the limiting factor in maintaining a positive nitrogen balance, regardless of protein intake.

None of the studies reviewed examined the effects of aerobic exercise and strength training on protein requirements. Protein is oxidized during endurance exercise and it is used for muscle repair and muscle protein synthesis in body builders. Thus, it is hypothesized that the protein requirements for an athlete participating in regular aerobic exercise and moderate to high intensity strength training may be greater than the requirements of an athlete who does not regularly perform both modes of exercise.

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