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Branched-Chain Amino Acids

Branched-Chain Amino Acids (BCAAs) are three essential amino acids that benefit muscle growth. Because they’re present in high levels notably in animal protein, supplementation is unnecessary for most people.

Our evidence-based analysis on branched-chain amino acids features 143 unique references to scientific papers.

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Summary of Branched-Chain Amino Acids

Primary information, health benefits, side effects, usage, and other important details

Branched Chain Amino Acids (BCAAs) refers to three amino acids: leucine, isoleucine, and valine.

For people with low dietary protein intake, BCAA supplementation can promote muscle protein synthesis and increase muscle growth over time. Supplementation can also be used to prevent fatigue in novice athletes.

Leucine plays an important role in muscle protein synthesis, while isoleucine induces glucose uptake into cells. Further research is needed to determine valine’s role in a BCAA supplement.

Supplementing BCAAs prevents a serum decline in BCAAs, which occurs during exercise. A serum decline would normally cause a tryptophan influx into the brain, followed by serotonin production, which causes fatigue.

BCAAs are important to ingest on a daily basis, but many protein sources, such as meat and eggs, already provide BCAAs. Supplementation is unnecessary for people with a sufficiently high protein intake (1-1.5g per kg of bodyweight a day or more).

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How to Take

Recommended dosage, active amounts, other details

The standard dosage for isoleucine is 48-72mg per kilogram of bodyweight, assuming a non-obese person. The standard leucine dosage is between 2-10g. A combination dose is 20g of combined BCAAs, with a balanced ratio of leucine and isoleucine.

Isoleucine is used for increasing glucose uptake into cells, while leucine is used to improve muscle protein synthesis.

BCAA supplementation is not necessary if enough BCAAs are provided through the diet. Further research is needed to determine valine’s optimal dosage and reason for supplementation.

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Human Effect Matrix

Unlocked for Examine members

The Human Effect Matrix summarizes human studies to tell you what effects Branched-Chain Amino Acids has on your body, how much evidence there is, and how strong these effects are.

Full details are available to Examine members.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-b Minor Moderate See all 4 studies
An increase in time to exhaustion appears to exist in prolonged endurance exercise, but this benefit may only exist in untrained or lightly trained individuals. Several studies have noted that the anti-fatigue effects and increased time to exhaustion do not really occur in advanced athletes
grade-b Minor Low See all 3 studies
In prolonged exercise and somewhat related to the antifatigue effects, an increase in fat oxidation is noted with BCAA supplementation; this is thought to be related to the glycogen preserving effects of BCAAs.
grade-b Minor Moderate See all 8 studies
A decrease in fatigue (mental fatigue when measured after the workout) results when BCAA supplementation is taken during exercise at a dose above 10g or so
grade-b - High See all 3 studies
There does not appear to be any reliable or significant changes in blood lactate concentrations following exercise with BCAA supplementation
- See study
Human studies suggest time-dependent influences on ammonia (increase after exercise up until 2 hours, a reduction the next day) while animal studies suggest that overdosing BCAAs can reverse a reduction into an increase
grade-c Minor - See study
The increased processing accuracy appears to be secondary to reducing exercise-related fatigue, and occurs when testing is after exercise.
grade-c Minor - See study
There is some evidence to support a reduction in the rate of perceived exertion during exercise under the influence of BCAA supplementation, but this appears to unreliably improve performance and is of low magnitude
grade-c Minor - See study
A (beneficial) decrease in reaction time has been noted during a stimulated soccer test, which was thought to be secondary to the antifatigue effects. Hypothesized to be useful for prolonged sports
grade-c Minor - See study
The weight loss that occurs during prolonged strenuous exercise (in these examples, skiing) are attenuated with BCAA supplementation relative to carbohydrate. This is likely indicative of lean mass and/or hydration, and is not necessarily an anti-fat loss effect
grade-c - - See study
No significant influence on adrenaline concentrations
grade-c - - See study
No significant performance enhancing effect on short-term cardiovascular exercise
grade-c - Moderate See 2 studies
There does not appear to be a likely alteration in blood glucose concentrations per se with BCAA supplementation, but the increased fat oxidation may attenuate the decline in glucose seen during prolonged exercise (which would appear to be a relative increase at later time points)
grade-c - - See study
No significant interactions with BCAA supplementation and cortisol
grade-c - - See study
Similar to the other catecholamines (adrenaline and noradrenaline), serum dopamine does not appear to be altered with supplemental BCAAs.
grade-c - Very High See 2 studies
No significant alterations in heart rate noted with BCAA supplementation at rest or during exercise
grade-c - - See study
No significant influence of BCAA supplementation on fasting insulin levels
grade-c - - See study
No significant alterations in formation of ketone bodies, which may be due to the ketogenic BCAA (leucine) being offset by the other two glucogenic ones
grade-c - Moderate See 2 studies
No significant influence on muscle soreness when assessed 2-3 days after exercise that is preloaded with BCAA supplementation
grade-c - - See study
BCAA supplementation does not appear to significantly influence noradrenaline concentrations in serum
grade-c - - See study
Oxygen uptake during anaerobic cardiovascular exercise does not appear to be modified with BCAA supplementation
grade-c - Moderate See 2 studies
Mixed effects on power output, but when it does occur it is not a per se increase in power output but secondary to reduced muscular soreness after repeated exercise. This may be more indicative of anti-fatigue effects than of genuine power output improvement

Studies Excluded from Consideration

  • Multinutrient supplement (included non-BCAA supplements)[1]

  • Confounded with non-BCAA amino acids (such as citrulline or glutamine)[2]

  • Paired with ACE inhibitors[3]

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Things to Note

Primary Function:

Also Known As


Do Not Confuse With

Leucine, Isoleucine, or Valine (all individual BCAAs)

  • There has been a reported stimulatory effect with BCAA supplementation, but due to a lack of research into this topic, the placebo effect cannot be ruled out as a cause.

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Click here to see all 143 references.