Saturday, April 4, 2009

“Goods” and “bads” of extra protein in sports

While Dietary Reference Intakes for protein are 0.8g protein per kg for adults, data suggest athletes may need more depending on their sport, particularly strength-training athletes (1). Research also indicates that even non-athletes who weight train may benefit from the added protein (2). Endurance exercise sports such as cycling and running increase protein turnover, including a lot more oxidation amino acids, so it is suggested that extra protein would also be wise (3;4).

However, many athletes often exceed intake required (5). While the positive balance may not affect competitiveness, excessiveness does not encourage further muscle growth or strength gain (5). It should also be noted that strength-training itself also encourages improved utilization of dietary protein possibly reducing need of added protein (5). When consumed with carbohydrate, net protein balance during and after endurance exercise is improved, but there is little evidence of actual improved performance due to the extra protein (3). There is also little evidence that the extra protein will stimulate muscle growth or strength (6).

Because daily requirements for protein are set by amount of protein lost, any extra protein should be added to make up for the loss and to maintain nitrogen balance (5). Protein intake that is excessive can lead to potential complications such as in the kidneys (if disease is onset) (7-10) and possible bone fracture if acidosis occurs (11).

Reference List

1. Phillips SM. Dietary protein for athletes: from requirements to metabolic advantage. Appl Physiol Nutr Metab 2006;31:647-54.
2. Evans WJ. Protein nutrition, exercise and aging. J Am Coll Nutr 2004;23:601S-9S.
3. Gibala MJ. Protein metabolism and endurance exercise. Sports Med 2007;37:337-40.
4. Tarnopolsky M. Protein requirements for endurance athletes. Nutrition 2004;20:662-8.
5. Phillips SM. Protein requirements and supplementation in strength sports. Nutrition 2004;20:689-95.
6. Dohm GL. Protein nutrition for the athlete. Clin Sports Med 1984;3:595-604.
7. Pecoits-Filho R. Dietary protein intake and kidney disease in Western diet. Contrib Nephrol 2007;155:102-12.
8. Manninen AH. High-protein diets are not hazardous for the healthy kidneys. Nephrol Dial Transplant 2005;20:657-8.
9. Friedman AN. High-protein diets: potential effects on the kidney in renal health and disease. Am J Kidney Dis 2004;44:950-62.
10. Donini LM, Pinto A, Cannella C. [High-protein diets and obesity]. Ann Ital Med Int 2004;19:36-42.
11. Mardon J, Habauzit V, Trzeciakiewicz A et al. Long-term intake of a high-protein diet with or without potassium citrate modulates acid-base metabolism, but not bone status, in male rats. J Nutr 2008;138:718-24.