In general, athletes have high intakes of branched-chain amino acids (BCAAs) because of their high energy and protein intakes. Many athletes have even higher intakes due to BCAA supplementation. How does supplementation affect performance? If you ingest a sufficient amount of BCAAs from food and protein supplements is it necessary to supplement with them? Michael Gleeson answered those questions at the 4th Amino Acid Workshop.
Key points from: 4th Amino Acid Workshop Interrelationship between Physical Activity and Branched-Chain Amino Acids - Michael Gleeson
"Higher total energy intakes and therefore higher protein intakes. The BCAA’s, leucine, isoleucine, and valine represent 3 of the 30 amino acids that are used in the formation of proteins. Thus, on average, the BCAA content of food proteins is about 15% of the total amino acid content.
Deliberate consumption of high-protein diets and protein supplements. Debate has always raged over how much dietary protein is required for optimal athletic performance, partly because muscle contains a large proportion of the protein in a human body (about 40%). Muscle also accounts for 25% to 35% of all protein turnover in the body. Both the structural proteins that make up the myofibrils and the proteins that act as enzymes within a muscle cell can change as an adaptation to exercise training.
Consumption of protein hydrolysates or mixtures of essential amino acids during and after exercise. Protein hydrolysates are produced from purified protein sources (e.g. casein) by heating with acid or, more usually, by addition of proteolytic enzymes followed by purification procedures. Such hydrolysates contain peptides of which up to about 40% may be dipeptides and tripeptides. Consumption of amino acids as dipeptides and tripeptides results in faster absorption into the blood stream compared to the ingestion of whole proteins or single amino acids. This is a desirable characteristic for athletes who wish to maximize amino acid delivery to muscles, although whether this has a practical effect of improving muscle protein synthesis, accretion of muscle mass, or improved recovery from exercise, has not yet been established.
In the late 1970’s, BCAAs were suggested to be the third fuel for skeletal muscle after carbohydrate and fat. BCAAs are sometimes supplied to athletes in energy drinks to provide extra fuel. Claims have also been made that BCAA supplementation can reduce net protein breakdown in muscle during exercise, reduce fatigue, and enhance performance via effects on the brain.
BCAAs as a fuel for exercise
Although early studies suggested that BCAAs could act as a fuel during exercise in addition to carbohydrate and fat, it has been shown that the activities of the enzymes involved in the oxidation of BCAAs are too low to allow a major contribution of BCAAs to energy expenditure. Detailed studies with a C-labeled BCAA (C-leucine) showed that the oxidation of BCAAs only increase 2 to 3-fold during exercise, whereas the oxidation of carbohydrate and fat increases 10 to 20-fold. Also, carbohydrate ingestion during exercise can prevent the increase in BCAA oxidation. BCAAs, therefore, do not seem to play a major role as a fuel during exercise, and from this point of view, the supplementation of BCAAs during exercise is unnecessary.
BCAAs and protein turnover
The claims that BCAAs reduce protein breakdown were initially based on early in vitro studies, which showed that adding BCAAs to an incubation or perfusion medium stimulated tissue protein synthesis and inhibited protein degradation. Several in vivo studies in health individuals failed to confirm the positive affect on protein balance that had been observed in vitro. However, several studies in recent years have inferred an anabolic effect of leucine or the BCAAs on muscle protein breakdown and a stimulatory effect on muscle protein synthesis (see the article by Dwight Matthews in this supplement for a review). Very recent work suggests the leucine itself, not its metabolites, acts as a signal to stimulate protein synthesis. "