5–10 g around training. With a protein-rich diet they add little extra.
In cirrhosis they reduce complications and improve albumin and liver enzymes.
View the study (meta-analysis) →They reduce muscle damage and soreness after exercise; for building muscle, total protein matters more.
View the study (meta-analysis) →⏱ 3 min read
Branched-chain amino acids, or BCAAs, are three essential amino acids with a characteristic branched side-chain chemical structure: leucine, isoleucine, and valine; they share several unusual properties that justify grouping them functionally: they are metabolized mainly in skeletal muscle (not in the liver like most amino acids), they make up about a third of muscle protein by mass, and leucine specifically activates the mTOR pathway responsible for initiating postprandial muscle protein synthesis, a signaling role unique among individual amino acids.
These properties have made BCAAs one of the most popular supplements in the world of fitness and strength sports over the past three decades, marketed as aids to preserve muscle mass in a calorie deficit, speed up recovery after intense training, and reduce central fatigue during prolonged exertion; rigorous clinical data from the past ten years have considerably qualified some of these commercial promises, showing a more conservative pattern in which an adequate intake of good-quality complete protein covers practically all of the postulated benefits of isolated BCAAs, an important conclusion for understanding the real place of these supplements in sports nutrition.
Activation of mTOR by leucine is real and well documented: doses of 2-3 grams of leucine (roughly equivalent to 20-30 grams of high-quality complete protein) are enough to maximize the postprandial muscle protein synthesis response, an effect called the "leucine threshold"; however, this isolated mTOR activation does not produce net protein synthesis without the simultaneous presence of the other essential amino acids (especially lysine, methionine, threonine, tryptophan, phenylalanine), which are the necessary building blocks, which reduces the usefulness of BCAAs on their own.
A study published in Frontiers in Physiology in 2017 with healthy volunteers showed that BCAA intake alone increases muscle protein synthesis only modestly compared with a high-quality complete protein source (whey), a limitation that calls into question the usefulness of isolated BCAAs as a post-workout supplement in people with adequate dietary protein intake.
In reducing delayed-onset muscle soreness (DOMS) after intense eccentric exercise, several trials have shown modest reductions in markers of muscle damage (creatine kinase, myoglobin) and in subjective pain with pre- and post-workout supplementation of 5-20 grams of BCAAs; the effects are quantitatively modest and depend significantly on baseline nutritional status (people with low protein intake benefit more than those who already consume 1.6-2.2 g/kg/day of protein).
An interesting hypothesis suggests that BCAAs during prolonged exercise could reduce central fatigue by competing with tryptophan for entry into the central nervous system (thereby reducing the synthesis of brain serotonin associated with fatigue); the clinical data along this line are inconsistent, with marginal benefits in some studies and none in others, without reaching robust conclusions.
A less popular clinical indication but with reasonable support is hepatic encephalopathy and advanced cirrhosis: in cirrhosis with malnutrition, BCAA supplementation improves nutritional status and liver function and reduces complications, a recognized indication with clinical trial data from several countries; specific preparations for this indication are available as medicines in some countries.
The doses studied for sports indications range from 5 to 20 grams daily, typically in a 2:1:1 ratio of leucine:isoleucine:valine (the "natural" ratio found in human muscle protein); for hepatic encephalopathy, specific doses of 12-20 grams/day according to regulated formulations; typical commercial products are dissolvable powders, tablets, or capsules with a variable amount per dose.
For most people with adequate protein intake (1.6-2.2 g/kg/day from complete sources such as fish, eggs, meat, dairy, legumes, and whey), isolated BCAAs provide no significant clinical benefit over the complete protein in the diet and are generally unnecessary; they may have a place in specific situations such as fasted training (where they are preferred over complete protein because of faster absorption), in people with suboptimal protein intake due to dietary restrictions, or in advanced liver cirrhosis with encephalopathy.
Generally well tolerated; the adverse effects described are rare and mild (digestive discomfort, the unpleasant bitter taste characteristic of the powder); people with amyotrophic lateral sclerosis should be cautious because of data suggestive of increased mortality in some studies; in people with maple syrup urine disease they are absolutely contraindicated because of a congenital metabolic enzyme defect; in pregnancy and breastfeeding the specific data as a supplement are limited, although usual dietary intake poses no problems.
Information, not medical advice. Scientific evidence reflects the quality of the studies.