Do Extra Amino Acids and Protein Build Bigger Muscles?

Martin J. Gibala, Ph.D.
McMaster University

Do athletes really need massive amounts of protein or amino acid supplements to maximize muscle growth? For many body builders and strength athletes, the answer is "yes." But what do the experts on sports nutrition and exercise physiology say? Leading scientific organizations such as the American College of Sports Medicine, American Dietetic Association and Dieticians of Canada have concluded that athletes have only slightly higher protein requirements than sedentary individuals. Moreover, the vast majority of athletes consume protein in their normal diets in excess of any increased requirement. Provided that sound nutritional practices are followed and energy intake is sufficient to maintain body weight, strength athletes require about 15% of their total caloric intake from protein and do not need to fortify their diets with expensive protein or amino acid supplements.

While most athletes do not need "extra" protein, there is compelling scientific evidence to indicate that the timing of amino acid intake can profoundly affect the muscle protein response to heavy resistance exercise. An acute bout of weightlifting exercise increases the rates of both protein synthesis and protein breakdown in muscle for many hours following a workout. However, in the absence of food intake, the rate of breakdown exceeds synthesis, and thus weightlifters actually lose muscle protein if they do not eat during recovery! It appears that a surprisingly small dose of essential amino acids can markedly stimulate muscle protein anabolism during recovery from resistance exercise. Several studies have shown that ingesting a solution containing 6 g of essential amino acids promotes a small, transient net increase in muscle protein balance that persists for 1-2 hours following drink ingestion. Stimulation of muscle protein synthesis by essential amino acids is a saturable process, and thus ingesting a single massive dose of amino acids in hopes of further promoting muscle anabolism seems futile. Non-essential amino acids appear unnecessary for stimulation of muscle protein balance, and co-ingestion of carbohydrate seems to provide little further benefit when at least 6 g of essential amino acids are ingested.

As a practical recommendation, strength athletes should consume about 0.1 g of essential amino acids per kilogram of body weight, either immediately prior to heavy resistance exercise or during the first few hours of recovery. Given that the 'anabolic boost' following amino acid ingestion is transient and returns to basal levels within 1-2 hours, ingesting repeated small doses of essential amino acids during recovery may be an effective strategy to optimize muscle accretion. Although most studies have examined the effect of specific amino acid mixtures, this does not mean that athletes need to consume amino acid solutions, and it is likely that high-quality proteins contained in 'real' foods (e.g., skim milk, yogurt, fish, chicken) are just as effective for promoting muscle anabolism following resistance exercise. Few studies have examined the effect of resistance training combined with protein ingestion on muscle protein accretion. However, preliminary evidence suggests that the specific type of protein consumed during habitual training does not markedly alter the hypertrophy response.