MVIIIHealth The MVIII app
← Back

Research · Supplements

BCAAs and EAAs

BCAAs raised muscle protein synthesis 22% over placebo in one trial, less than complete protein produces. BCAAs did not preserve lean mass during a 16-week diet. Meta-analyses find less soreness for 1 to 4 days after damaging exercise. Amino acid supplements added muscle mass and strength in older adults. Liver disease trials reported more nausea and diarrhea.

Add to Bio HackChecked 2026-11-09
Status
Dietary supplements in the US.
Also called
branched-chain amino acids, BCAA, leucine, isoleucine, valine, essential amino acids, EAA, leucine-enriched EAA, intra-workout aminos
Taken for
muscle growth, muscle protein synthesis, less soreness, recovery, preserving muscle while dieting, aging muscle, fasted training

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help3

Reported risks3

What people take it for, and what was found

Shown to help3

Moderate

Muscle protein synthesis

Shown to raise muscle protein synthesis for hours, by 22% in one trial of trained men, but less than complete protein. Lean mass did not change in older adults.

The numbers and sources
Effect
In 10 resistance-trained young men, 5.6 g of BCAAs after training raised myofibrillar protein synthesis to 0.110%/h against 0.090%/h on placebo, 22% higher [1]. A review of human studies found BCAAs transiently stimulate protein synthesis, but less than a complete protein source with all essential amino acids [2]. In older adults, leucine supplements raised the fractional synthetic rate (SMD 1.08, 95% CI 0.50 to 1.67) in 9 RCTs, with no change in lean body mass (SMD 0.18, 95% CI -0.18 to 0.54) or leg lean mass [3].
Population
Young trained men [1]; older adults [3].
Sources
[1], [2], [3]
Caveats
Synthesis rates over hours do not predict muscle gained over months, as the leucine meta-analysis shows [3]. The 2017 trial was funded in part by GlaxoSmithKline [1]. Reference [2] is a narrative review.
Strong

Muscle soreness and damage after hard exercise

Shown to reduce muscle soreness 24 to 96 hours after damaging exercise in active adults, with larger effects at higher doses and longer use.

The numbers and sources
Effect
Across 18 RCTs, BCAAs reduced soreness at 24 hours (g -1.34), 48 hours (g -1.75), 72 hours (g -1.82) and 96 hours (g -0.82). Creatine kinase was lower immediately (g -0.44) and at 72 hours (g -0.99), but not at 24, 48 or 96 hours; LDH did not change. Higher daily and total doses and longer use were linked to larger effects [4]. A second meta-analysis of 9 RCTs found reduced soreness 24 to 72 hours after exercise, mainly in trained people with mild to moderate damage, at doses up to 255 mg per kg a day [5].
Population
Healthy active adults after damaging resistance or endurance exercise [4][5].
Sources
[4], [5]
Caveats
The authors of [5] report high variability between studies by training status, dose and timing. Soreness is self-rated.
Moderate

Muscle mass and strength in older adults

Shown to improve strength and muscle mass modestly in older adults, for supplements rich in BCAAs, including EAA and whey products.

The numbers and sources
Effect
Across 35 RCTs in older people, BCAA-rich supplements, a category that included EAA and whey protein products, improved strength (SMD 0.35, 95% CI 0.15 to 0.55), muscle mass (SMD 0.25, 95% CI 0.10 to 0.40) and physical performance (SMD 0.29, 95% CI 0.00 to 0.57). EAA supplements improved handgrip strength more than whey protein in subgroup analysis [7]. In 52 patients having knee replacement, 9 g a day of EAAs from 1 week before to 2 weeks after surgery left rectus femoris area at 134% of baseline at 2 years against 114% on placebo, and quadriceps strength at 159% against 125%. Clinical outcomes did not differ [8]. In 10 RCTs and one prospective study of people with sarcopenia, leucine groups differed from placebo in handgrip strength (p = 0.03), appendicular muscle mass and gait speed (p = 0.008) [9].
Population
Older adults [7]; knee replacement patients [8]; 1,133 people over 65 with sarcopenia [9].
Sources
[7], [8], [9]
Caveats
High heterogeneity, and 14 of 35 trials had potential bias [7]. The pooled supplements are not pure BCAA products. The leucine review rated its evidence low quality and found leucine alone of limited benefit without other therapy [9].

Not shown to help1

Limited

Lean mass during dieting

One trial found BCAAs did not significantly reduce lean mass loss over 16 weeks of dieting in 132 adults, and a high-protein diet lost the least.

The numbers and sources
Effect
In 132 adults with overweight or obesity on a 500 kcal daily deficit for 16 weeks, lean mass fell 4.39% with BCAAs (0.1 g per kg a day), 5.39% with placebo and 3.67% with a high-protein diet (p = 0.06). Insulin sensitivity did not differ among groups [6].
Population
132 Chinese adults aged 21 to 45 [6].
Sources
[6]
Caveats
One RCT. The high-protein diet group lost the least lean mass [6].

Doses studied

The muscle protein synthesis trial used 5.6 g of BCAAs after training [1]. The dieting trial used 0.1 g per kg a day of BCAAs for 16 weeks [6]. Soreness trials ranged widely; one meta-analysis reported effects at up to 255 mg per kg a day [5], and the other found larger effects with higher daily and total doses [4]. The knee replacement trial used 9 g a day of EAAs for 3 weeks around surgery [8].

Risks

Reported risks2

LimitedVery common

Nausea and diarrhea

Limited evidence: in people with cirrhosis, nausea and diarrhea occurred in 12% on BCAAs against 3% on control, with a very uncertain estimate.

The numbers and sources
How common
Very common: more than 1 in 10 people.
Effect
In a Cochrane review of trials in liver disease, nausea and diarrhea, counted as serious adverse events, occurred in 58 of 477 people (12%) on BCAAs and 16 of 538 (3%) on control diets. The pooled estimate was very uncertain (RR 2.05, 95% CI 0.40 to 10.58) [11].
Population
1,015 participants in 6 trials of people with cirrhosis and hepatic encephalopathy [11].
Sources
[11]
Caveats
Certainty was very low. Ten of the review's 18 trials gave BCAAs by mouth and eight intravenously [11]. People with cirrhosis are not the population taking BCAAs for training.
LimitedHow often is not known

Insulin resistance

Linked to insulin resistance and later diabetes when blood BCAA levels are high, in observational studies. A 16-week trial of BCAA supplements found no change in insulin sensitivity.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
A systematic review of 23 studies (20,091 participants) found higher circulating BCAAs associated with insulin resistance and later diabetes risk [10]. In the 16-week dieting RCT, BCAA supplements did not change insulin sensitivity against placebo [6].
Population
Observational cohorts [10]; adults with overweight or obesity [6].
Sources
[6], [10]
Caveats
The observational studies measured blood BCAA levels, not supplement use, and cannot show that supplements cause insulin resistance.

Mixed results1

LimitedHow often is not known

Contamination and label accuracy

Mixed results: five BCAA products held on average 61% of the labeled amount, while a European test of amino acid supplements found EAA and BCAA contents matched their labels.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
An enzyme assay of five sport BCAA supplements found free BCAA content averaged 61% of the amount claimed on the label (p < 0.01) [12]. A test of 16 sport supplements from several European countries found 6 of 19 amino acids in whey protein products outside the EU's 20% label tolerance, while the declared amounts in the essential and branched-chain amino acid supplements matched what was measured [13]. No product survey testing BCAA or EAA supplements for contaminants was located.
Population
5 BCAA products [12]. 16 sport supplements from European countries [13].
Sources
[12], [13]
Caveats
The first study is a single-author conference abstract with no product names [12]. The second does not give the number of BCAA and EAA products in its abstract [13]. Both are small samples of the market.

Claims tested and not found

  1. That BCAAs build as much muscle as protein. BCAAs stimulate muscle protein synthesis less than a complete protein [2], and leucine raised synthesis without adding lean mass in older adults [3].
  2. That BCAAs protect muscle during a diet. Lean mass loss with BCAAs did not differ meaningfully from placebo over 16 weeks, and a high-protein diet lost the least [6].

Sources

  1. Jackman SR, Witard OC, Philp A, et al. Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis following Resistance Exercise in Humans. Frontiers in Physiology. 2017. https://doi.org/10.3389/fphys.2017.00390
  2. Kaspy MS, Hannaian SJ, Bell ZW, et al. The effects of branched-chain amino acids on muscle protein synthesis, muscle protein breakdown and associated molecular signalling responses in humans: an update. Nutrition Research Reviews. 2023. https://doi.org/10.1017/s0954422423000197
  3. Xu ZR, Tan ZJ, Zhang Q, et al. The effectiveness of leucine on muscle protein synthesis, lean body mass and leg lean mass accretion in older people: a systematic review and meta-analysis. British Journal of Nutrition. 2014. https://doi.org/10.1017/s0007114514002475
  4. Salem A, Ben Maaoui K, Jahrami H, et al. Attenuating Muscle Damage Biomarkers and Muscle Soreness After an Exercise-Induced Muscle Damage with Branched-Chain Amino Acid (BCAA) Supplementation: A Systematic Review and Meta-analysis with Meta-regression. Sports Medicine - Open. 2024. https://doi.org/10.1186/s40798-024-00686-9
  5. Weber MG, Dias SS, de Angelis TR, 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. https://doi.org/10.1007/s00726-021-03089-2
  6. Ooi DS, Ling JQR, Sadananthan SA, et al. Branched-Chain Amino Acid Supplementation Does Not Preserve Lean Mass or Affect Metabolic Profile in Adults with Overweight or Obesity in a Randomized Controlled Weight Loss Intervention. Journal of Nutrition. 2021. https://doi.org/10.1093/jn/nxaa414
  7. Bai GH, Tsai MC, Tsai HW, et al. Effects of branched-chain amino acid-rich supplementation on EWGSOP2 criteria for sarcopenia in older adults: a systematic review and meta-analysis. European Journal of Nutrition. 2021. https://doi.org/10.1007/s00394-021-02710-0
  8. Ueyama H, Kanemoto N, Minoda Y, et al. Perioperative Essential Amino Acid Supplementation Facilitates Quadriceps Muscle Strength and Volume Recovery After TKA. Journal of Bone and Joint Surgery. 2023. https://doi.org/10.2106/jbjs.22.00675
  9. Huang C, Hsieh MH. Effects of Leucine Supplementation in Older Adults with Sarcopenia: A Meta-Analysis. Nutrients. 2025. https://doi.org/10.3390/nu17152413
  10. Zhao X, Han Q, Liu Y, et al. The Relationship between Branched-Chain Amino Acid Related Metabolomic Signature and Insulin Resistance: A Systematic Review. Journal of Diabetes Research. 2016. https://doi.org/10.1155/2016/2794591
  11. Aamann L, Deshpande N, Dam G, et al. Branched-chain amino acids for people with cirrhosis and hepatic encephalopathy. Cochrane Database of Systematic Reviews. 2026. https://doi.org/10.1002/14651858.CD001939.pub5
  12. Eley B. Quantitative analysis of branched-chain amino acids in five nutritional supplements using a leucine dehydrogenase assay (P23-004-19). Current Developments in Nutrition. 2019. https://doi.org/10.1093/cdn/nzz043.p23-004-19
  13. Di Stefano V, Cicero N, Melilli MG, et al. Proteins and protein components for sportspeople: quality control of dietary supplements. Natural Product Research. 2024. https://doi.org/10.1080/14786419.2023.2218974

Everything in the library