PROTEIN: POWER OR PUFFERY?

Jeffrey J. Zachwieja, PhD Senior Scientist, Gatorade Sports Science Institute

Daily Protein Needs

Digestion of dietary protein yields amino acids, which, after being absorbed, are available for metabolism and the growth and repair of all tissues in the body. Because many athletes are purposefully trying to add more muscle, most believe the protein content of the diet should be considerably higher than that of non-athletes.  It is true that on average, athletes require slightly more protein (1.2-1.5 g/kg body weight; 0.5-0.7 grams/lb) than do less-active people (0.8-1.0 g/kg body weight; 0.4-0.5 grams/lb).  However, it is far from true that in order to meet this additional need, athletes must rely upon protein and amino acid supplements.  Further, there is simply no scientific evidence to support the idea that the protein or amino acids in supplements are more effective for athletes than protein in ordinary foods.

New Notions

Protein is typically consumed away from activity, often during meals or snacks before or after an athletic event or practice.  Lately, research focused on how protein intake during exercise may improve performance has caught the attention of sports scientists, coaches, and athletes alike.  Similarly, studies on whether or not protein intake immediately before or after exercise can enhance the recovery process have generated a high level of interest.  The purpose of this brief review is to clarify what has been reported and identify practical applications of the findings.  Two topics will be covered: 1) the ingestion of protein and amino acids immediately before and after exercise and 2) the ingestion of protein and amino acids during exercise.

Protein Before and After Exercise

Effect on muscle glycogen resynthesis

The ability of the body to recover from games, practices or an intense workout requires adequate rest and proper nutrition.  Consuming carbohydrate shortly after exercise will facilitate the restoration of muscle glycogen (stored carbohydrate energy), which is an important component of the recovery process.  Some believe that a mixture of carbohydrate and protein will speed up this process, but that contention is not supported by the prevailing science.  At least five carefully controlled studies have shown that adding protein, amino acids or protein hydrolysates to a carbohydrate supplement is no more effective for muscle glycogen resynthesis than ingesting equal calories of carbohydrate alone.^1-5

Effect on muscle protein synthesis

Consuming foods or beverages containing small amounts of protein shortly before or after exercise, especially weight-training exercise may still be of value.  Research has demonstrated that ingestion of amino acids alone⁶ or in combination with carbohydrate⁷ after weight-training exercise stimulates protein synthesis and improves net protein balance in muscle.  In the presence of carbohydrate, it appears that only small amounts of essential amino acids (e.g., as little as 6 grams) are required for the positive effect.  Data are not yet available for the effect of whole proteins, amino acid dose-response or the impact of different forms of training on muscle protein synthesis.  The newest research is most intriguing, it suggests that muscle protein synthesis is stimulated more when a carbohydrate amino acid drink is consumed before vs. immediately after weight training exercise⁸.  Still, athletes and coaches should cautiously incorporate these nutritional practices into their routines.  The research represents only a “snapshot” view of the dynamic process of muscle protein metabolism and in no way can it be taken to mean these practices will lead to bigger, stronger muscles.

Protein During Exercise

Effect on performance

Only a few amino acids can be used by muscles for energy and their oxidation accounts for only 2-5% of the total energy expenditure, even during intense exercise. Most of the energy for exercise comes from carbohydrate and fat.  The best scientific studies have been unable to show that branched-chain amino acid ingestion during exercise benefits performance^9,10.  In fact, a potential side effect of amino acid ingestion during exercise is excess ammonia accumulation (a by-product of amino acid breakdown), which could contribute to fatigue¹¹.

It has been suggested that consuming a protein-carbohydrate mixture during exercise will raise blood insulin to higher levels than carbohydrate alone, increasing the use of carbohydrate in muscle to better delay fatigue.  Although there are a few published abstracts that point to such a conclusion, these studies have yet to be published in a peer-reviewed scientific journal, so it is impossible to determine the validity of the results. At this point, we can only conclude on the basis of published research that ingesting amino acids (and likely protein) during exercise has no effect on exercise performance. Although future publications may provide a different perspective, it is hard to imagine how ingesting small quantities of protein or amino acids during exercise could benefit performance.  For example, if higher blood insulin levels did result from ingesting a protein-carbohydrate drink during exercise, this could possibly reduce fat oxidation and fatty-acid availability. Well-trained athletes have an incredible ability to use fat as a fuel.  In fact, this helps them save carbohydrate for when it’s needed the most; for example, during a finishing sprint.  Along these lines, there are no good scientific data to show that ingesting protein along with carbohydrate during exercise spares the use of muscle glycogen or increases the uptake and use of blood glucose by muscle.

Bottom Line

Athletes are always searching for a competitive edge and often look to a supplement or special combination of nutrients to find it. Research has shown, however, that there are no magic-bullet supplements for improving sports performance and, while a cornerstone nutrient for the athletic diet, protein is also not a magic bullet. Protein plays an important role in helping the body recover from training and competition and a balanced nutrition shake or bar may be an effective way to jump-start this process. The common-sense approach to improve performance, backed by lots of research, is to rely on a sound, fundamental program that stresses hydration and nutrition as a complement to an effective training program.

References

¹ Jentjens, R., L. van Loon, C. Mann, A. Wagenmakers, A. Jeukendrup.  Additional protein and amino acids to carbohydrates does not enhance postexercise muscle glycogen synthesis.  J. Appl. Physiol.  91:839-846, 2001.

² Carrithers, J., D. Williamson, P. Gallagher, M. Godard, K. Schulze, S. Trappe.  Effects of postexercise carbohydrate-protein feedings on muscle glycogen restoration.  J. Appl. Physiol.  88:1976-1982, 2000.

³ Rotman, S., J. Slotboom, R. Kreis, C. Boesch, E. Jequier.  Muscle glycogen recovery after exercise measured by 13C-magnetic resonance spectroscopy in humans: effect of nutritional solutions.  MAGMA 11:114-121, 2000.

⁴ Van Hall, G., S. Shirreffs, J. Calbet.  Muscle glycogen resynthesis during recovery from cycle exercise: no effect of additional protein ingestion.  J. Appl. Physiol.  88:1631-1636, 2000.

⁵ Van Loon, L., W. Saris, M. Kruijshoop, A. Wagenmakers.  Maximizing postexercise muscle glycogen synthesis: carbohydrate supplementation and the application of amino acid or protein hydrolysate mixtures.  Am. J. Clin. Nutr.  72:106-111, 2000.

⁶ Tipton, K., A. Ferrando, S. Phillips, D. Doyle, R. Wolfe.  Postexercise net protein synthesis in human muscle from orally administered amino acids.  Am. J. Physiol.  276:E628-E634, 1999.

⁸ Rasmussen, B., K. Tipton, S. Miller, S. Wolf, R. Wolfe.  An oral essential amino acid-carbohydrate supplement enhances muscle protein anabolism after resistance exercise.  J. Appl. Physiol.  88:386-392, 2000.

⁹ Tipton, K., B. Rasmussen, S. Miller, S. Wolf, S. Owens-Stovall, B. Petrini, R. Wolfe.  Timining of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise.  Am. J. Physiol.  281:E197-E206, 2001.

¹⁰ Davis, M., R. Welsh, K. De Volve, N. Alderson.  Effects of branched-chain amino acids and carbohydrate on fatigue during intermittent, high-intensity running.  Int. J. Sports Med.  20:309-314, 1999.

¹¹ Van Hall, G., J. Raaymakers, W. Saris, A. Wagenmakers.  Ingestion of branched chain amino acids and tryptophan during sustained exercise in man: failure to affect performance.  J. Physiol.  486:789-794, 1995.

¹² MacLean, D., T. Graham, B. Saltin.  Stimulation of muscle ammonia production during exercise following branched chain amino acid supplementation in humans.  J. Physiol.  493:909-922, 1996.