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What are BCAAs?

Proteins are made from 20 amino acids, some of which the body can make itself (non-essential) and some of which must be consumed in the diet (essential). The branched chain amino acids (or BCAAs) are the three essential amino acids of leucine, isoleucine and valine. Together, they make up 35% of the essential amino acids contained in muscles(1). They are ‘essential’ because they must be consumed in the diet, as the body cannot make them out of other amino acids. BCAAs are naturally found in foods that are high in protein, with the highest concentrations found in animal protein, including meat and dairy foods.


What do they do?

BCAAs are referred to as ‘branched chain’ amino acids because of their special molecular structure. From an exercise perspective, BCAAs are especially relevant as our muscles can use them to provide energy during exercise but also because they are required to stimulate the process of muscle protein synthesis. In this regard, the BCAA leucine is the main BCAA that is used to produce energy during exercise and is also the key amino acid that stimulates muscle protein synthesis in the post-exercise recovery period(2).


When can they be used?

BCAAs consumed in “free form” require minimal digestion and are rapidly absorbed into the blood stream; therefore, they can be taken up by muscles during exercise. Given that exercise suppresses muscle protein synthesis whilst concomitantly increasing muscle protein breakdown (i.e. inducing a negative muscle protein balance), it is useful to ingest BCAAs prior to or during exercise(3). In this way, muscle protein breakdown is reduced and muscle protein synthesis can be increased in the post-exercise recovery period. Additionally, BCAAs can also be consumed immediately post-exercise so as to stimulate muscle protein synthesis and facilitate training adaptations.

If you are a vegetarian then you may also struggle to get sufficient amounts of BCAAs within your normal diet. Although soy protein contains a full “essential” amino acid profile, the BCAA levels are lower than in sources such as whey. As such, vegetarian or vegan athletes may therefore benefit from consuming BCAAs before, during and/or after exercise.

Fasted training has become a popular way to manage your body composition and promote aerobic adaptations in muscle, but exercising with low carbohydrate availability can mean the body is more prone to using BCAAs for energy metabolism(4). Consuming BCAAs before and/or during low carbohydrate training may help prevent muscle breakdown. Research has suggested that BCAA supplementation (particularly leucine enriched protein feeding) does not impair free fatty acid availability or fat oxidation during exercise in a carbohydrate restricted state. This can help the athlete undergo fasted training, while promoting muscle adaptations(5).

Advanced Isolate+ contains 9g of BCAAs, including 5g of leucine. This is the ideal shake to have before or after exercise. WHEY20’s also provide 7g of BCAAs, without the need for water and shakers. Use these before, during and/or post work-out or throughout the day to get your 20-25g of protein every 3-4 hours(6).


Are they good to use during resistance training?

The aim of resistance or strength training is to make the muscle stronger by altering its structure and often involves muscle growth (i.e. muscle hypertrophy). Given that the BCAAs are especially important in stimulating muscle protein synthesis (i.e. the process underpinning muscle hypertrophy), then it is useful to also consume BCAAs before, during and/or after strength training sessions. Indeed, consuming a sub-optimal dose of whey protein but supplemented with additional BCAAs can induce equivalent rates of muscle protein synthesis to that induced by 25 g of whey protein (7, 8).


What about endurance sports?

Given that prolonged and intense endurance exercise increases muscle protein breakdown (as it uses our muscle BCAA pool to contribute to energy production), it is useful to ingest BCAAs before, during and/or after such activity. In this way, muscle protein breakdown can be reduced during exercise and muscle protein synthesis can be increased in the recovery period.

BCAA supplementation with endurance training may also facilitate adaptations in aerobic power and post-exercise recovery in trained athletes (9).


Take home messages

  • “Free form” BCAAs are absorbed rapidly into the blood-stream thus meaning they can be delivered to our muscles quickly.
  • Supplementing with BCAAs before, during and/or after a work-out may help reduce muscle breakdown, muscle soreness and increase protein synthesis.
  • Strength training: BCAAs are most commonly used to stimulate muscle protein synthesis in the post-exercise recovery period where leucine provides the “trigger” to switch on the process.
  • Endurance training: BCAAs are used to contribute to energy production during exercise (especially if undertaken with low carbohydrate availability). Consuming BCAAs prior to or during endurance exercise can therefore reduce muscle protein breakdown whilst also promoting muscle protein synthesis in the post-exercise recovery period.



  1. Kephart, W. C., Wachs, T. D., Mac Thompson, R., Mobley, C. B., Fox, C. D., McDonald, J. R., & Pascoe, D. D. (2016). Ten weeks of branched-chain amino acid supplementation improves select performance and immunological variables in trained cyclists. Amino Acids48(3), 779-789.
  2. Pasiakos, S. M., McClung, H. L., McClung, J. P., Margolis, L. M., Andersen, N. E., Cloutier, G. J., & Young, A. J. (2011). Leucine-enriched essential amino acid supplementation during moderate steady state exercise enhances postexercise muscle protein synthesis. The American Journal of Clinical Nutrition94(3), 809-818.
  3. MacLean, D. A., Graham, T. E., & Saltin, B. (1994). Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise. American Journal of Physiology-Endocrinology And Metabolism, 267(6), 1010-1022.
  4. Wagenmakers, A. J., Beckers, E. J., Brouns, F. R. E. D., Kuipers, H. A. R. M., Soeters, P. B., Van Der Vusse, G. J., & Saris, W. H. (1991). Carbohydrate supplementation, glycogen depletion, and amino acid metabolism during exercise. American Journal of Physiology-Endocrinology and Metabolism260(6), 883-890.
  5. Impey, S. G., Smith, D., Robinson, A. L., Owens, D. J., Bartlett, J. D., Smith, K., & Morton, J. P. (2015). Leucine-enriched protein feeding does not impair exercise-induced free fatty acid availability and lipid oxidation: beneficial implications for training in carbohydrate-restricted states. Amino Acids47(2), 407-416.
  6. Witard, O. C., Jackman, S. R., Breen, L., Smith, K., Selby, A., & Tipton, K. D. (2014). Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise. The American Journal of Clinical Nutrition, 99(1), 86-95.
  7. Churchward-Venne, T. A., Breen, L., Di Donato, D. M., Hector, A. J., Mitchell, C. J., Moore, D. R., … & Phillips, S. M. (2014). Leucine supplementation of a low-protein mixed macronutrient beverage enhances myofibrillar protein synthesis in young men: a double-blind, randomized trial. The American Journal of Clinical Nutrition99(2), 276-286.
  8. Churchward‐Venne, T. A., Burd, N. A., Mitchell, C. J., West, D. W., Philp, A., Marcotte, G. R., … & Phillips, S. M. (2012). Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men. The Journal of Physiology590(11), 2751-2765.
  9. Jafari, H., Ross, J. B., & Emhoff, C. A. W. (2016). Effects of Branched-Chain Amino Acid Supplementation on Exercise Performance and Recovery in Highly Endurance-Trained Athletes. The FASEB Journal30(1), 683
Written By

Ted Munson (Performance Nutritionist)

Ted is a Performance Nutritionist here at Science in Sport.