BCAAs: Leucine, Isoleucine and Valine
What branched-chain amino acids are, what trials show for muscle soreness, athletes, older adults and liver disease, and safety points including maple syrup urine disease.
Content last updated . This page has not been medically reviewed.
What is BCAAs (leucine, isoleucine, valine) good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Building blocks of body proteins
Established roleLeucine, isoleucine and valine are three of the nine essential amino acids, which the body cannot make and must get from food. Amino acids are the building blocks of proteins.
Supplements: Normal protein-building role is not proof that extra BCAA powders help people who already eat enough protein.
Muscle soreness after hard exercise
Preliminary or mixedIn a review of 10 trials, seven found less muscle soreness 24 to 72 hours after damaging exercise. The authors judged it useful mainly in trained people after mild to moderate muscle damage.
Supplements: Mixed to promising; authors could not say whether it works in untrained people or at higher amounts. Less soreness is not the same as better performance.
Muscle strength and size in older adults
Preliminary or mixedA pooled analysis of 35 trials found small improvements in strength, muscle mass and physical performance with BCAA-rich supplements in older adults. The studies differed a lot, so results need caution.
Supplements: Preliminary: small gains, high variation between trials; supplements were BCAA-rich mixtures, not always BCAAs alone.
Performance and body composition in athletes
Preliminary or mixedA review of 24 athlete studies found BCAAs tended to switch on muscle-building signals, but effects on performance and body composition were minimal. Results in endurance sports were inconsistent.
Supplements: Benefits were minimal; most studies did not report total daily protein, which limits interpretation.
Hepatic encephalopathy in cirrhosis
Preliminary or mixedIn people with cirrhosis, BCAAs may reduce hepatic encephalopathy (a brain problem caused by liver failure), but the certainty of the evidence is low. Effect on survival is very uncertain.
Supplements: Low-certainty evidence in a medical setting only; not a supplement claim for healthy people.
Energy source
Established roleThe body can use amino acids as an energy source.
Supplements: Normal protein-building role is not proof that extra BCAA powders help people who already eat enough protein.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (3)
- Muscle RecoveryPreliminary or mixed
Some trials found less muscle soreness after hard exercise, mainly in trained people; results vary.
- Healthy AgingPreliminary or mixed
BCAA-rich supplements gave small gains in muscle strength and mass in older adults in pooled trials with high variation.
- Recovery OptimizationPreliminary or mixed
Less soreness 1 to 3 days after damaging exercise was found in several trials, but this is not proof of better performance.
Body systems (4)
- Bones, Joints & MusclesPreliminary or mixed
Some pooled studies found less soreness after hard exercise and small gains in older adults; results vary and benefits for athletes were minimal.
- Musculoskeletal SystemPreliminary or mixed
Some pooled studies found less soreness after hard exercise and small gains in older adults; results vary and benefits for athletes were minimal.
- Nervous SystemDocumented risk
In maple syrup urine disease these amino acids build up and are toxic to the brain and other organs, so people with it should avoid BCAA products unless their metabolic team advises.
- Hepatic / Liver SystemPreliminary or mixed
In people with cirrhosis, BCAAs may reduce hepatic encephalopathy, but certainty is low. This is a medical setting, not self-treatment.
Body parts (3)
- BrainDocumented risk
In maple syrup urine disease, build-up of these three amino acids is toxic to the brain.
- MusclesPreliminary or mixed
Some pooled studies found less soreness after hard exercise and small gains in older adults; results vary and benefits for athletes were minimal.
- LiverPreliminary or mixed
Studied in cirrhosis with hepatic encephalopathy (low-certainty evidence, medical setting). Not advice for healthy people.
Functional actions (1)
- Muscle RecoveryPreliminary or mixed
Seven of 10 trials found less soreness 24 to 72 hours after damaging exercise, mainly in trained people. Evidence varies with dose and design.
Habits (2)
- ExercisePreliminary or mixed
BCAAs are studied around hard exercise; soreness benefits appeared mainly in trained people.
- Resistance TrainingPreliminary or mixed
Reviews found less soreness in resistance-trained people, but little effect on performance or body composition.
Conditions & symptoms (4)
- Maple Syrup Urine DiseaseDocumented risk
An inherited disorder in which leucine, isoleucine and valine build up and are toxic to the brain and other organs. People with it should not take BCAA products unless their metabolic team says so.
- Hepatic EncephalopathyPreliminary or mixed
In people with cirrhosis, BCAAs may reduce hepatic encephalopathy (low-certainty evidence from 18 trials); effect on survival is very uncertain. Medical setting only.
- Liver CirrhosisPreliminary or mixed
The cirrhosis trials looked at hepatic encephalopathy as the outcome; nausea and diarrhoea were recorded more often with BCAAs, though that difference is very uncertain.
- SarcopeniaPreliminary or mixed
BCAA-rich supplements gave small improvements in muscle strength, mass and physical performance in older adults in pooled trials, with high variation between studies.
Documented risks and interactions (1)
- Risk when the body cannot break them down (maple syrup urine disease). In this inherited disorder leucine, isoleucine and valine build up and are toxic to the brain and other organs.
Overview
BCAA stands for branched-chain amino acids: leucine, isoleucine and valine. All three are on MedlinePlus's list of the nine essential amino acids, which the body cannot make and must get from food. [1] They are found in many foods, particularly protein-rich ones such as milk, meat and eggs. [2] BCAA powders and capsules isolate just these three.Of the three, leucine has had the most attention because of its ability to stimulate the initial acute anabolic response (the first step in muscle-building signals). [3] A switched-on signal is not the same as more muscle, so this page focuses on outcomes measured in people. Leucine has its own guide: leucine, mTOR and muscle protein synthesis.
Information only. A clinician, pharmacist or dietitian can say whether a product suits a particular person.
How the evidence is labeled
Established nutritional role means the body needs it. Evidence in adequately nourished people means trials in healthy people eating enough protein. Mixed, promising but limited and insufficient evidence mean what they say. Biomarker results (such as a blood enzyme) are kept separate from outcomes people feel or can measure in daily life.| Question | What the sources found | Evidence label |
|---|---|---|
| Needed by the body? | Essential; must come from food. [1] | Established nutritional role |
| Muscle soreness after hard exercise | A systematic review (10 trials, 9 in the meta-analysis) found seven studies where BCAAs reduced soreness 24 to 72 hours later; the authors could not say whether BCAAs work in untrained people or at higher doses. [4] A separate meta-analysis of 18 studies found lower creatine kinase (a muscle-damage blood marker) and soreness, but no effect on lactate dehydrogenase. [5] | Mixed to promising; a blood marker is not the same as better performance |
| Performance and body composition in athletes | A systematic review of 24 studies found BCAAs tended to activate anabolic signals but benefits on performance and body composition were negligible. [6] | Mixed; most studies did not report total daily protein [6] |
| Strength and muscle size | A narrative review calls BCAA efficacy an ongoing source of controversy in sports nutrition. [3] | Mixed |
| Older adults | A meta-analysis of 35 trials of BCAA-rich supplements found small improvements in strength, muscle mass and physical performance, with high heterogeneity and a call for caution. [7] | Promising but limited |
| Cirrhosis with hepatic encephalopathy | The 2026 Cochrane review (18 trials, 934 adults) found low-certainty evidence that BCAAs reduce hepatic encephalopathy and very uncertain, possibly little, effect on death. [8] | Medical setting; not self-treatment |
| Compared with protein foods or whole protein | A review of muscle supplements rated BCAA evidence as mixed or unclear. [9] Head-to-head page: BCAAs vs EAAs vs complete protein. | Mixed |
The older-adult and sarcopenia (age-related muscle loss) topics are covered further on sarcopenia and muscle loss.
What blood levels do and do not mean
A meta-analysis of nine studies found that plasma BCAA concentrations were associated with type 2 diabetes incidence across follow-up periods. [10] That is an association with blood levels, not proof that eating or supplementing BCAAs causes diabetes, and it was not a trial of supplements. Anyone worried about blood sugar should speak with a clinician.Forms and amounts
Products vary in how much of each of the three they contain and in what else is added; the label is the only guide, and "BCAA" on the front does not tell you the ratio. See reading an amino acid supplement label.Amounts in studies are not recommendations. The soreness meta-analysis noted effects at doses of up to 255 mg per kilogram of body weight per day and could not conclude about higher doses. [4]
No national health agency has set a tolerable upper intake level for individual amino acids. [11] Researchers working under a nonprofit amino acid science council proposed upper levels of 35 g a day of leucine for young adults and 30 g a day for older adults from clinical studies in healthy people. [11] These are research proposals, not official limits, and say nothing about people with kidney or liver disease.
Related
Essential amino acids · BCAA exercise evidence · Protein for muscle, training and recoveryFrequently asked questions
Are BCAAs the same as essential amino acids?
No. BCAAs are three of the nine essential amino acids. [1]
Do BCAAs prevent muscle soreness?
Some meta-analyses found less soreness, especially in trained people with mild to moderate muscle damage, but studies differ in dose and design. [4][5]
Do I need BCAAs if I eat enough protein?
A systematic review in athletes found negligible benefits on performance and body composition, and most studies did not report total protein intake. [6]
Who should avoid BCAA supplements?
People with maple syrup urine disease, because these amino acids build up in the body. [2] Anyone with liver or kidney disease, who is pregnant, or who takes prescribed medicine should ask a clinician or pharmacist first.
Do high BCAA blood levels cause diabetes?
Studies show an association between higher blood levels and later type 2 diabetes. That does not show that supplements cause it. [10]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Side effects and precautions
- In the cirrhosis trials, nausea and diarrhea were recorded in 12% of people on BCAAs and 3% of people in the diet comparison groups, although the review calls the evidence about this difference very uncertain. [8]
- Maple syrup urine disease is an inherited disorder in which the body cannot process certain amino acids properly; leucine, isoleucine and valine build up to levels that are toxic to the brain and other organs. [2] A person with this condition should not take BCAA products unless their metabolic team says so.
- Liver and kidney disease, pregnancy, breastfeeding, children: the Cochrane review found no trials in children, [8] and the sources read give no supplement guidance for pregnancy or kidney disease. Ask a clinician first. See amino acid supplements in pregnancy, children and older adults and liver safety.
- Medicines: read how interactions work; ask a pharmacist, and never stop a prescribed medicine on your own.
- Before surgery: list every supplement for your surgical team (supplements before surgery).
- Sport: products can be contaminated or contain banned substances; see sports certification and banned substances.
References
- MedlinePlus. Amino acids. National Library of Medicine, US. Review date 1/21/2025. Read 2026-10-22.
- MedlinePlus Genetics. Maple syrup urine disease. National Library of Medicine, US. Read 2026-10-22.
- Plotkin DL et al. Isolated leucine and branched-chain amino acid supplementation for enhancing muscular strength and hypertrophy: a narrative review. Int J Sport Nutr Exerc Metab. 2021. Read 2026-10-22.
- Weber MG et al. The use of BCAA to decrease delayed-onset muscle soreness after a single bout of exercise: a systematic review and meta-analysis. Amino Acids. 2021. Read 2026-10-22.
- Salem A et al. Attenuating muscle damage biomarkers and muscle soreness after exercise-induced muscle damage with BCAA supplementation: systematic review and meta-analysis. Sports Med Open. 2024. Read 2026-10-22.
- Martinho DV et al. Oral branched-chain amino acids supplementation in athletes: a systematic review. Nutrients. 2022. Read 2026-10-22.
- Bai GH et al. Effects of branched-chain amino acid-rich supplementation on EWGSOP2 criteria for sarcopenia in older adults: systematic review and meta-analysis. Eur J Nutr. 2022. Read 2026-10-22.
- Aamann L et al. Branched-chain amino acids for people with cirrhosis and hepatic encephalopathy. Cochrane Database Syst Rev. 2026. Read 2026-10-22.
- Valenzuela PL et al. Supplements with purported effects on muscle mass and strength. Eur J Nutr. 2019. Read 2026-10-22.
- Ramzan I et al. Circulating branched chain amino acids and the temporal risk of type 2 diabetes: systematic review and meta-analysis. Nutrients. 2022. Read 2026-10-22.
- Elango R. Tolerable upper intake level for individual amino acids in humans: a narrative review of recent clinical studies. Adv Nutr. 2023. Read 2026-10-22.