This is a fairly straightforward answer now, thanks to decades of research and likely millions of dollars in research money. Before I dive into it, though, I’m going to provide a little additional background over amino acids and proteins as a whole. Amino acids are for the most part the bricks that when added together make a house. Except in this scenario a house is a protein. The human body primarily uses 20 different amino acids to make cellular proteins. One mistake I made when I first started learning about amino acids and proteins was that I didn’t really even consider other tissues besides muscle. Because of my interests in resistance training, exercise and nutrition; I focused my thoughts primarily on skeletal muscle. Proteins, however make up a part of every cell in our body and we have trillions of them.
Amino acids are primarily categorized into three areas: nonessential, conditionally essential and essential and using this system, amino acids are grouped relative to the body’s ability to produce them. Nonessential amino acids are readily produced by the body and as a result getting them from dietary sources is not critical. If the body needs more of them, it simply will produce more. Conditionally essential amino acids are unique because the body can produce them and oftentimes produces them readily. However, if situations develop whereby the body needs an increased amount, the body may not be able to produce enough to meet body demands. Hence, the supply of these amino acids is essential only during certain conditions. Two key examples of this are glutamine and arginine. Both amino acids have become distinctly popular in sports nutrition and it’s largely based on the theory that increasing their supply prevents the body from having to breakdown other cellular protein sources, of which skeletal muscle is a primary reservoir. Essential amino acids are called such because the body cannot produce them and as a result their dietary availability is an absolute prerequisite or they are essential to the diet. Common thought suggests that eight essential amino acids exist although in my field I commonly see references to their being nine or even ten amino acids which are essential amino acids. No matter how many there are, they must be consumed by your diet.
Initial concern related to protein centered on making a determination what the daily requirement for protein was for athletes and active individuals. There are many different perspectives and recommendations on this depending on which organization you look at or who you ask. The America Dietetic Association suggests protein requirements for adults should be 0.8 grams per kilogram of body mass (0.4 grams per pound), which comes out to around 65–85 grams of protein each day for an average adult . Certainly if you’re smaller or larger than the average person these numbers will adjust. As it became more evident that protein needs were indeed significantly increased for strength/power athletes, research began to wonder if different proteins types made a difference and what role did amino acids play in the differences. Studies performed in the early 1990’s (before protein supplementation was a widely accepted practice) recommended that strength/power athletes have daily protein requirements of around 1.4 grams for every kilogram of body mass [2-3] while endurance athletes actually have a little higher requirement around 1.5 to 1.6 grams of protein for every kilograms of body mass . As it has become more accepted that higher protein intakes were needed for active individuals, the interest in specific amino acids or combinations of them became more and more popular.
As common knowledge as it may seem now, the first step for researchers was to determine if an increased or abundant supply of amino acids after exercise actually increased muscle protein synthesis. It did , but the amino acids were infused in high amounts and as a result don’t carry over well to oral consumption of protein and amino acids. Those studies were quickly to follow and fortunately, oral ingestion of just 6 grams of essential amino acids significantly increased muscle protein synthesis several fold above baseline levels [6-7]. The next important study compared whether ingesting a mixed dose of nonessential and essential amino acids or just the essential amino acids impacted muscle protein synthesis to varying degrees . When subjects ingested 13 grams of essential amino acids along with 35 grams of a carbohydrate, the increases in muscle protein synthesis were of a similar degree as when a similar dose of essential amino acids and an additional dose of nonessential amino acids was provided. In other words, when considering what type of amino acids to ingest or include as part of a workout/nutrition regimen, nonessential amino acids provided no additional benefit to muscle protein synthesis in this particular study. Only the essential amino acids were needed to increase muscle protein synthesis, which is a result which has also been shown in older adults as well . In addition, studies began to show that a dose-dependent response may occur; the more you take, the higher muscle protein synthesis is increased. .
The optimal dose of amino acids continues to be a relevant question not only for exercising and bodybuilding folk, but also for individuals who are sick and otherwise rapidly losing muscle tissue. Until a few years ago, a series of research studies illustrated that maximal levels of muscle protein synthesis could be stimulated with ingesting doses of essential amino acids ranging anywhere from six to ten grams [6-7, 10-11]. While these results are great, we typically don’t ingest amino acids in free form, but rather in the form of protein supplementation or food. To address this question, researchers from McMaster University in Canada had a group of six healthy men complete an intense bout of lower-body exercise before ingesting no protein, 5, 10, 20 or 40 grams of whole egg protein . For those of you who may be turning your nose up at egg protein, egg as a protein source is actually considered to be a quality protein with reasonable protein efficiency ratios and PDCAA scores, but not on the standard of even an average quality whey protein. The authors measured muscle protein synthesis and found that the rate of muscle protein synthesis was significantly increased in comparison to resting values after ingesting all doses of protein. This is important to understand because it basically says that rather small and even rather large doses of protein all increase muscle protein synthesis, so keep taking your post-workout protein drink! If you’re hell bent on figuring out how much is too much, the answers aren’t very clear yet. According to this particular study, the authors found that ingesting 10 grams of protein stimulated greater values than 5 grams, 20 grams was greater than both 10 grams, but there were no differences between 20 and 40 grams . These results correspond very nicely with all of the studies mentioned previously which indicated that a 6–10 gram dose of essential amino acids stimulates muscle protein synthesis [6-7, 13].
I’ll be the first to mention that the average body mass of the six men in this study was 190 pounds (86 kg) and it stands to reason that individuals with larger body mass (or especially a greater muscle mass) will be able to process more amino acids. It’s important to note that excess protein consumption has never been shown to be harmful. In performance (resistance, endurance or hybrid) athletes who are serious about improving performance (including muscle growth) it’s better to err on the side of too much so that your body can continue to recover and grow at its optimal rate. This way you will be sure not to handcuff progress. For those of you that like to take a exceptionally large dose (50g or more), you may think about spreading the same dose out by a couple of hours as increases in blood amino acid levels and protein synthesis typically only stay elevated for two hours at a time .
In summary, essential amino acids are critically important for stimulating muscle protein synthesis. If you’re serious about your health and positive responses to your training, regular ingestion of a high-quality protein source which contains a healthy dose of essential amino acids is essential, no pun intended.
- Shils, M.E., et al., eds. Modern Nutrition in Health and Disease. 9th ed. 1999, Lippincott Williams & Wilkins: Baltimore, MD.
- Lemon, P.W., et al., Protein requirements and muscle mass/strength changes during intensive training in novice bodybuilders. J Appl Physiol, 1992. 73(2): p. 767-75.
- Tarnopolsky, M.A., et al., Evaluation of protein requirements for trained strength athletes. J Appl Physiol, 1992. 73(5): p. 1986-95.
- Campbell, B., et al., International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr, 2007. 4: p. 8.
- Biolo, G., et al., Increased rates of muscle protein turnover and amino acid transport after resistance exercise in humans. Am J Physiol, 1995. 268(3 Pt 1): p. E514-20.
- Borsheim, E., et al., Essential amino acids and muscle protein recovery from resistance exercise. Am J Physiol Endocrinol Metab, 2002. 283(4): p. E648-57.
- Tipton, K.D., et al., Postexercise net protein synthesis in human muscle from orally administered amino acids. Am J Physiol, 1999. 276(4 Pt 1): p. E628-34.
- Tipton, K.D., et al., Nonessential amino acids are not necessary to stimulate net muscle protein synthesis in healthy volunteers. J Nutr Biochem, 1999. 10(2): p. 89-95.
- Volpi, E., et al., Essential amino acids are primarily responsible for the amino acid stimulation of muscle protein anabolism in healthy elderly adults. Am J Clin Nutr, 2003. 78(2): p. 250-8.
- Rasmussen, B.B., et al., An oral essential amino acid-carbohydrate supplement enhances muscle protein anabolism after resistance exercise. J Appl Physiol, 2000. 88(2): p. 386-92.
- Tipton, K.D., et al., Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise. Am J Physiol Endocrinol Metab, 2001. 281(2): p. E197-206.
- Moore, D.R., et al., Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr, 2009. 89(1): p. 161-8.
- Cuthbertson, D., et al., Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle. FASEB J, 2005. 19(3): p. 422-4.
- Bohe, J., et al., Latency and duration of stimulation of human muscle protein synthesis during continuous infusion of amino acids. J Physiol, 2001. 532(Pt 2): p. 575-9.