Title: Protein supplements in sport

 

Key words: protein, supplements, ergogenic, sport, protein metabolism, exercise, starved, carbohydrate, fat, muscle, protein requirements, negative nitrogen balance, adaptation, RNI, athletes, nitrogen balance, endurance, cyclists, bodybuilders, leucine, oxidation, urea excretion, glycogen, carbo-loading, oxoacid dehydrogenase, fatty acids, BCAA, branched chain fatty acids, high protein diet, diet, strength accretion, lean body mass, training, power events, sports physiology, rowing, wrestling, field sports, metabolic pathways, metabolism, metabolic efficiency, body building, DRV, daily recommended values, protein supplements, athletic performance

 

Date: Oct 2006

 

Category: Sport

 

Nutrimed Module:

 

Type: Article

 

Author: Morgan, G

 

Protein supplements in sport

Protein supplements are widely used as ergogenic aids in sport. Their use has highlighted various methodological problems which has hampered research into protein metabolism and the value of such supplements in increasing performance. These issues relate to:

1. The type, intensity and duration of the exercise.

2. The duration of the study.

3. Whether trained or untrained individuals were used.

4. The sex, age and race of the participants.

5. Design details such as whether the subjects were starved, and their nutritional status vis-ŕ-vis carbohydrate and fat intake before, during and after the exercise sessions.

 

Short-term and poorly controlled studies in untrained subjects have invariably overstated daily protein requirements. Hard or unaccustomed exercise leads to muscle damage which requires many days to repair and results in a negative nitrogen balance and increased protein demands (Newham 1983). Adaptation to this increased protein demand may take 8-18 days depending on the activity involved (Oddoye & Margen 1979). With training, adaptation occurs more quickly and has been shown to occur at levels of 1 g/Kg/day (Gontzea 1975), barely above the protein RNI of 0.75 g/Kg/day, indicating greater energetic and metabolic efficiency.

 

Allowing for the short-term effects of adaptation , it is nonetheless the case that regular exercise does increase daily protein requirements. Nitrogen balance studies in trained athletes have shown conclusively an increased demand, ranging from 1.2 g/Kg/day for endurance athletes (Meredith 1989) to 1.8 g/Kg/day for cyclists participating in the Tour de France (Brouns 1989). Intakes higher than 2 g/Kg/day have been reported for bodybuilders (Celejowa &Homa 1970). These findings are in keeping with studies that show increased leucine (a branched chain amino acid(BCCA)) oxidation and increased urea excretion with increasing rates of exercise (Wolfe 1984,1987, Rennie 1994).

 

In trained athletes the following points have emerged:

1. Reduced glycogen reserves during prolonged exercise leads to greater protein turnover (Anderson (1990).

2. Carbo-loading and the more efficient utilisation of fatty acids during endurance training reduces the demands on protein catabolism (Graham 1991, Rennie 1994).

3. Heavy prolonged exercise, especially over 2 hours, leads to activation of oxoacid dehydrogenase and the utilisation of BCAAs a source of fuel (Hood & Terjung 1987, Tarnopolsky 1991).

 

Taken together these facts support Chittenden’s (1907) findings that switching from a high protein diet to a high carbohydrate and modest protein intake of 1 g/Kg/day is sufficient to bring about significant improvements in strength endurance in athletes. This is in keeping with Forbes’ (1985) finding that lean body mass is stable in athletes and is able to tolerate increases in strength and endurance. This may be less true for strength accretion as it is known that body builders are known to lay down significant amounts of new muscle during the course of their training (Millward 1994) and the same would be expected for power events such as rowing, wrestling or field sports.

 

In summary it has been shown that exercise increases protein demand but that this increase is partially compensated for by increased metabolic efficiency, especially by using carbohydrate and fatty acid metabolic pathways. With body building and during intensive periods of training when muscle is being broken down and laid down, protein demands are increased (Lemon 1990, Tarnopolsky 1988). Type, intensity and duration of the activity is critical in determining the level of these demands.

 

Given the increased energy demands of sportsmen, as has been pointed out by Millward (1994), these demands can be more than met through a well balanced diet. Millward’s figures for a 15.5 Kg weight gain in athletes over a 3 year period lead to an estimated 3-4% increment over the protein DRV (DOH 1991). Taking into account genetic factors and the chronicity of training programmes in trained athletes, the increased protein requirement is likely to be significantly less than this figure and would be more than covered by the increases dietary intake. There are thus no grounds for taking protein supplements in an effort to boost athletic performance.

 

References

1. Newham DJ, McPhail G, Mills KR, Edwards RHT. (1983) Ultra- structural changes after concentric and eccentric contractions of human muscle. J Neurol Sci 61: 109-132

2. Oddoye EB & Margen S. (1979) Nitrogen balance studies in humans: long-term effect of high nitrogen intake on nitrogen accretion. J Nutr 109: 363-77

3. Gontzea I, Sutzescu P, Dumitrache S. (1975) The influence of adaptation to physical effort on nitrogen balance in man. Nutrition Reports International 11: 23

4. Meredith CN, Zackin MJ, Frontera WR, Evans WJ. (1989) Dietary protein requirements and body protein metabolism in endurance- trained men. J Appl Physiol 66: 2850-2856

5. Brouns F, et al. (1989) Eating, drinking, and cycling. A controlled Tour de France simulation study, part II. Effect of diet manipulation. Int J Sports Med 10 (suppl 1), S41-S48

6. Celejowa I & Homa M. (1970) Food intake, nitrogen and energy balance in Polish weight lifters during a training camp. Nutr and Metab 12: 259-74

7. Wolfe RR. (1984) Tracers in Metabolic Research: Radioisotope and Stable Isotope/Mass Spectometry Methods. AR Liss, New York

8. Wolfe RR. (1987) Does exercise stimulate protein breakdown in humans? Isotopic approaches to the problem. Med Sci Sports Exercise 19: 172-178

9. Rennie MJ, Bowtell JL, Millward DJ. (1994) Physical activity and protein metabolism. In: Physical Activity, Fitness and Health (Bouchard C, Shepherd RJ & Stephens T. ed). Champaigne, Ill.: Human Kinetics Publishers

10. Anderson DE & Sharp RL. (1990) Effects of muscle glycogen depletion on protein catabolism during exercise. Med Sci Sports Exercise 22 (2,suppl), S59

11. Graham TE, Kiens B, Hargreaves M, Richter EA. (1991) Influence of fatty acids on ammonia and amino acid flux from active human muscle. Am J Physiol 261: E168-E176

12. Hood DA & Terjung RL. (1987) Effect of endurance training on leucine in perfused rat skeletal muscle. Am J Physiol 253: E648- E656

13. Tarnopolsky MA, et al. (1991) Whole body leucine metabolism during and after resistance exercise in fed humans. Med Sci Sports Exercise 23: 326-33

14. Chittenden RH. (1907) The Nutrition of Man. London: Heinemann

15. Forbes GB. (1985) Body composition as affected by physical activity and nutrition. Federation Proceedings 44: 343-347

16. Millward DJ, Bowtell JL, Pacy P, Rennie MJ. (1994) Physical activity, protein metabolism and protein requirements. Proc Nutr Soc 53: 223-240

17. Lemon PWR, MacDougall JD, Tarnopolsky MA, Atkinson SA. (1990) Effect of dietary protein and body building exercise on muscle mass and strength gains. Can J Sport Sci 14 (4), 14S

18. Tarnopolski MA, MacDougall JD, Atkinson SA. (1988) Influence of protein intake and training status on nitrogen balance and lean body mass. J Appl Physiol 64: 187-93

19. Department of Health. (1991) Dietary reference values for food energy and nutrients for the United Kingdom. London. HMSO