BCAAs are essential amino acids that bodybuilders and athletes use to increase power output, reduce fatigue, and improve fat loss. However, excessive BCAA usage can have negative side effects, such as increasing the risk for type 2 diabetes and other conditions. Read on for further details on the potential effects of BCAA and their correct dosage.
What Are BCAAs?
There are three BCAAs: leucine, isoleucine, and valine, which are all essential amino acids – not produced by the body but needed for survival [1, 2].
BCAAs are the largest collection of amino acids in the body, accounting for up to 35% of muscle proteins. These amino acids (especially leucine) stimulate protein production in the muscles, possibly helping with muscle building and recover [1, 3, 4].
They also seem to promote sugar storage in the muscles. In animal studies, BCAAs (especially isoleucine) promoted blood glucose uptake into the muscles while blocking muscle carbohydrate (glycogen) breakdown [5, 6].
Normally, BCAAs are excreted rapidly. BCAA intermediates can be toxic at high concentrations, so functional BCAA breakdown is vital. Because BCAAs are broken down in the muscle rather than in the liver, they are thought to help produce energy during exercise [1, 2, 7].
BCAA formulas have been on the market since 1996, mainly for treating liver diseases such as cirrhosis and hypoalbuminemia .
Nowadays, BCAAs are mainly used by bodybuilders for exercise purposes, to increase energy, and boost protein synthesis (especially leucine) .
- Essential amino acids
- Approved for nitrogen loss
- May help recover from exercise and increase body lean mass
- May help with liver cirrhosis and its complications
- Unclear effects on exercise performance
- Excessive supplementation may trigger type 2 diabetes and ALS
- May cause high ammonia levels
- May interfere with the uptake of other essential amino acids
- Not recommended in people with insulin resistance, McArdle’s disease, and maple syrup urine disease
An injectable 4% BCAA formulation (BranchAmin) is approved by the FDA as a nitrogen source in people with severe nitrogen loss due to poor protein absorption or septic shock .
Possibly Effective for:
1) Exercise Recovery
BCAA supplements taken before and after exercise reduced exercise-induced muscle soreness and damage in 8 clinical trials on 134 people. This may speed up exercise recovery while preventing injuries [10, 11, 12, 13, 14, 15, 16, 17].
However, they were of little or no effectiveness in trials on 21 older volunteers performing a 2-day trail in the mountains and 30 well-trained men recovering from intense weight training [18, 19].
Supplementing with BCAAs seems to preserve muscle proteins by both preventing their breakdown and stimulating their production [20, 21, 22].
A meta-analysis of 8 clinical trials concluded that BCAA supplementation was better than rest alone for recovery after exercise due to its ability to reduce muscle soreness and function decline .
Physical Performance Decline
In 2 clinical trials on 21 athletes, BCAA supplementation reduced central fatigue after intense exercise [24, 25].
In 2 clinical trials on 27 well-trained people, BCAAs prevented the decline in power output after exercise [26, 15].
Cognitive Performance Decline
The reduced central fatigue caused by BCAA supplementation preserved the ability to couple movement and spatial perception (perceptual-motor skills) after exercise in a clinical trial on 9 tennis players .
In a trial of 12 volunteers, BCAA supplementation prevented the decline in short-term memory caused by exercise .
In another trial on 10 soccer players, BCAA supplements reduced the decline in reaction time by 10% .
Taken together, the evidence suggests that BCAAs may help with exercise recovery, especially by reducing muscle soreness and preserving its function. You may discuss with your doctor if you may add them to your training routine.
2) Increasing Lean Mass
In a clinical trial on 36 body-builders, BCAA supplements increased lean mass better than other supplements like carbohydrates and whey protein .
In another trial on 40 men, both low (6.25 g) and high (25 g) BCAA doses were similarly effective at promoting muscle building after exercise when supplemented with high levels (5 g) of leucine .
In 17 resistance-trained men on a low-calorie diet, BCAA supplementation maintained weight loss while preserving muscle mass. Similarly, elite wrestlers on a low-calorie diet lost more weight when supplemented with BCAAs in a clinical trial on 25 people [31, 32].
A high dietary consumption of BCAAs was associated with a reduced incidence of obesity in 2 observational studies on over 5,500 people [33, 34].
Supplementing with BCAAs and vitamin B6 failed to promote weight loss but reduced waist-to-hip ratio and preserved legs lean in a clinical trial on 42 overweight women .
BCAAs may also help prevent muscle loss in people at risk. In a study on 73 functionally-limited elderly people, high BCAA levels were associated with increased lean mass (both increased muscle section and reduced fat). Supplementation improved muscle mass and strength in 2 trials on 73 people with rheumatoid arthritis and 68 people with sarcopenia [36, 37, 38].
Although limited, the evidence suggests that BCAA supplementation may help both build muscle and lose fat. However, doing more exercise and improving your diet may be safer and more effective ways to obtain these benefits. You may discuss with your doctor if BCAAs may help as a complementary strategy.
3) Liver Damage and Complications
In 3 clinical trials on almost 700 people with liver cirrhosis, supplementation with BCAA granules increased survival and quality of life. The treatment was more effective when given during the night, probably because it helped spare proteins [39, 40, 41].
The survival rate without any detrimental event was around 63.6% with BCAA supplementation in another trial on 21 people with cirrhosis .
In a trial of 20 people with chronic hepatitis, 100 with cirrhosis, and 16 controls, BCAA supplementation greatly increased albumin in the blood, which leads to declines in both liver diseases. BCAAs were more effective in those with low blood albumin levels in another trial on 65 people with cirrhosis [43, 44].
In 2 trials on 92 people with cirrhosis, a high-fiber, high-protein diet supplemented with BCAAs improved nutritional status and muscle mass without increasing ammonia and glucose levels. BCAAs had similar effects in 2 other trials on 62 people with this condition [45, 46, 47, 48].
BCAAs in combination with ACE inhibitors delayed the progression of tissue scar in a clinical trial on 89 people with cirrhosis .
In 3 trials on over 100 people in which cirrhosis developed into inoperable liver cancer, BCAAs helped preserve liver function after chemotherapy delivery directly into the tumor (chemoembolization), resulting in an increased survival and quality of life [50, 51, 52].
In 2 clinical trials on over 150 people undergoing the surgical removal of liver cancer, supplementation with BCAAs improved protein metabolism, increased the chance of survival, and reduced its progression to cirrhosis [53, 54].
In people with liver damage, the reduced liver function causes several toxic substances to build up in the brain and cause damage (hepatic encephalopathy). For instance, the disturbed amino acid metabolism increases the uptake of aromatic amino acids over BCAA into the brain.
Two meta-analyses found that BCAA supplementation improved brain damage in people with liver cirrhosis, but had no effect on survival, quality of life, and nutritional status. A clinical trial on 27 people identified isoleucine as the amino acid most effectively improving this condition [55, 56, 57].
To sum up, the evidence suggests that BCAA supplementation may help with the overall health status in people with liver cirrhosis and its complications. You may discuss with your doctor if it may help as an add-on to your treatment regime. Because liver cirrhosis is a serious, life-threatening condition, never use BCAAs in place of what your doctor recommends or prescribes.
Insufficient Evidence for:
1) Exercise Performance
Exercise leads to amino acid usage. BCAAs become rapidly depleted after exercise, showcasing the possible beneficial effects of BCAA supplementation .
In a clinical trial on over 200 marathon runners, BCAA supplementation improved mental performance in all runners and running times only in the slowest ones .
In another trial of 10 endurance runners, the runners given BCAA supplements ran better times for two days in a row in both 5,000- and 10,000-m races .
Taking a supplement with valine and two non-branched amino acids (arginine and serine) on the 14 days before an intense cycling exercise improved endurance performance in a trial on 39 men .
BCAA supplementation maintained energy capacity by promoting fat breakdown once the glycogen stores had been depleted in a clinical trial on 7 healthy volunteers .
BCAA supplements also increased lactate threshold (LT) in a study of 8 volunteers. LT measures endurance capacity as any exercise below the LT means lactate does not build up in the muscles. Oxygen consumption (VO2) is a measure of LT and the study showed that overall VO2 measures increased by 13% and max VO2 increased by 4.2% .
In a trial of 7 cyclists, BCAA supplementation reduced the exertion that was perceived by the athletes by up to 7%. However, even if their exertion was lower, their exercise performance did not change .
However, not all studies found increased endurance performance and reduced fatigue after supplementing with BCAAs. This was the case in trials on 28 marathon runners, 10 cyclists, 24 skiers, 20 offshore sailors and [64, 65, 66, 27]
Furthermore, excessive BCAA supplementation may even cause fatigue by increasing ammonia production .
BCAAs may help with exercise consisting of intermittent sprints, as seen in 2 clinical trials on 22 well-trained handball players and 10 soccer players doing a treadmill exercise of changing intensity. However, they were ineffective in another trial on 8 people performing intermittent running [68, 28, 60].
In another trial on 13 canoeists, dietary leucine supplementation increased both upper body power and endurance performance .
In a small trial of 12 volunteers, BCAA supplements increased power output .
In another trial of 36 men, BCAA supplementation increased their muscle strength better than other supplements such as whey protein and carbohydrates .
This effect could be caused by increases in cortisol, as seen in a study of 10 volunteers. Cortisol controls the fight-or-flight response, which can flood muscles with glucose. This provides brief but great amounts of energy .
However, a study of 12 athletes found no increases in handgrip strength following BCAA supplementation .
Moreover, excessive BCAA supplementation can decrease exercise performance. A rat study showed that a 3.57% BCAA-supplemented diet increased swimming time until exhaustion by 37%. However, a higher (4.76%) BCAA-supplemented diet decreased swimming times by 43% compared to the controls .
Because most studies were small and the results are mixed, it’s difficult to determine for certain if BCAAs help with exercise performance. Larger, more robust clinical trials are needed to shed some light on this potential benefit.
Effects on Heart Rate
Although some BCAA users supplementing with BCAAs for the first time are concerned that they may increase their heart rate, science hasn’t found any evidence of this adverse effect.
In 3 trials on 30 people taking BCAA supplements and a study in rats, the supplements did not increase their heart rate and even reduced it in some cases [73, 71, 74, 75].
The increased heart rate seen by some users may be due to other components in the supplements such as caffeine.
2) Heart Failure
BCAA breakdown deficiencies are associated with an increased incidence of heart disease .
In a clinical trial on 18 people with heart failure and low blood albumin levels, BCAAs improved blood levels of this protein and reduced heart size. However, another trial on 66 people with this condition found that physical training improved the symptoms regardless of BCAA supplementation [77, 78].
In rat studies, BCAA supplementation improved outcomes after induced heart failure and cardiac cachexia (severe weight loss). It also caused :
- Decreased heart rate
- Increased heart function
- Increased survival time
- Decreased weight loss
- Increased mitochondrial function
A few human studies (with contradictory results) and some animal research cannot be considered sufficient evidence to support the use of BCAAs in people with heart failure. Further clinical research is needed.
3) Sleep Disturbances
In a clinical trial on 5 healthy men, infusion with BCAAs at night improved respiratory control, possibly helping reduce sleep apnea .
In a study of 7 patients with kidney failure, taking BCAA supplements at night increased rapid eye movement (REM) sleep and decreased end-tidal CO2 levels, which are important for dreaming and respiratory function during sleep .
Two small clinical trials are clearly insufficient to attest to the effectiveness of BCAAs at improving sleep disturbances. Larger, more robust clinical trials are needed to confirm these preliminary results.
Possibly Ineffective for:
In a weight-loss study of 500 participants, insulin resistance was associated with increased BCAA levels. In another study on over 2,400 people, type 2 diabetes was associated with higher blood BCAA levels. Similarly, urine leucine levels were significantly higher in 55 type 2 diabetes patients [81, 82, 83].
A meta-analysis concluded that an impaired BCAA may cause type 2 diabetes .
In a clinical trial of 27 people suffering from either insulin resistance or hepatitis C, BCAA supplements improved muscle insulin resistance in 10 of the patients .
However, most studies found that BCAA supplementation may cause type 2 diabetes.
In a 15-year study on 155 middle-aged women, increasing BCAA intake by up to 20% increased the risks of type 2 diabetes by 7% .
In another study on 140 people, a poor diet with excess of fats combined with BCAA supplementation contributed to the development of insulin resistance .
A recent meta-analysis of 8 studies associated high dietary BCAA intake with type 2 diabetes .
Limitations of BCAA Supplementation
BCAA mechanisms and amino acid ratios for treating muscle damage and soreness are still unknown .
Also, BCAA supplementation may interfere with the absorption of other amino acids because the blood-brain barrier uses similar mechanisms for them. Extra BCAA supplementation can lead to decreased absorption of tryptophan, tyrosine, and glutamine [88, 89].
Protein-rich foods such as chicken, turkey, beef, pork, milk, and cheese also have high BCAA contents .
BCAAs can be supplemented as:
The powder or lemonade forms taste worse but are the most popular. Capsules and tablets are less concentrated (meaning it’s necessary to take a lot of them) and the effects take longer to kick in because they are digested slower.
Because BCAA supplements are not approved by the FDA for any condition, there is no official dose. Users and supplement manufacturers have established unofficial doses based on trial and error. Discuss with your doctor if BCAAs may be useful as a complementary approach in your case and which dose you should take.
In one study, 0.087g/kg at a 2:1:1 leucine:isoleucine:valine ratio improved physical performance and decreased muscle soreness .
Leucine, one of the BCAAs, is safe for use up to a dose of 35 g/day in adult men .
It is recommended to take BCAA supplements before and after exercise to reduce muscle damage .
It is important to remember that excessive dosing can have the opposite effect and worsen performance. In one rat study, excessive BCAA supplements increased fatigue .
Although there is clinical data on toxic doses on rat studies, human data is not available .
Synergies with Other Supplements
In a trial of 10 endurance runners, combining BCAA supplements with arginine and citrulline supplements improved running time. While BCAA supplementation can increase ammonia levels, arginine and citrulline both decrease them, possibly having a protective effect .
Side Effects & Precautions
This list does not cover all possible side effects. Contact your doctor or pharmacist if you notice any other side effects.
Call your doctor for medical advice about side effects. In the US, you may report side effects to the FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch. In Canada, you may report side effects to Health Canada at 1-866-234-2345.
BCAA supplementation may increase ammonia levels in the blood (hyperammonemia), which increases fatigue and can lead to a variety of different brain disorders such as Reye syndrome and deficiencies of urea cycle enzymes [67, 59].
Amyotrophic Lateral Sclerosis (ALS)
ALS is one of the most common neuromuscular diseases, especially in athletes. This is caused by increased BCAA levels, which causes the toxic overexcitation of certain brain cells .
Decreased Absorption of other Amino Acids
Aromatic amino acids (phenylalanine, tyrosine, and tryptophan) compete with BCAAs for getting absorbed into the brain [94, 95].
BCAA supplements may reduce dopamine in the brain, since they may prevent its stimulation by phenylalanine and tyrosine [96, 97, 98].
Supplement/Herb/Nutrient-drug interactions can be dangerous and, in rare cases, even life-threatening. Always consult your doctor before supplementing and let them know about all drugs and supplements you are using or considering.
The combination of BCAAs with morphine increased the effectiveness and duration of the pain relief in isolated brain slices .
Due to its effects on blood and muscle sugar levels and its potential to cause insulin resistance, diabetics and prediabetics should be cautious with BCAA supplements.
Patients with McArdle’s disease take up and break down BCAAs at much higher rates. BCAA supplements may cause their heart rates to spike and their exercise performance to decrease .
Maple syrup urine disease is caused by deficiencies in the enzyme responsible for BCAA breakdown (branched-chain α-keto acid dehydrogenase). Because people with this condition have unusually high BCAA levels, supplementation may worsen their symptoms .
In a study of 150 people, BCAA levels were significantly higher in those with obesity. BCAA supplementation can lead to the activation of certain pathways such as mTOR, S6K1, and IRS1, ultimately causing insulin resistance .
Krüppel-like Factor 15 (KLF15) is a key regulator of the heart’s BCAA catabolic pathway. Defective KLF15 increases branched-chain α-keto acid (BCKA) levels, which are known to promote heart defects and failure .
The opinions expressed in this section are solely those of BCAA users, who may or may not have medical or scientific training. Their reviews do not represent the opinions of SelfHacked. SelfHacked does not endorse any specific product, service, or treatment.
Do not consider user experiences as medical advice. Never delay or disregard seeking professional medical advice from your doctor or other qualified healthcare providers because of something you have read on Selfhacked. We understand that reading individual, real-life experiences can be a helpful resource, but it is never a substitute for professional medical advice, diagnosis, or treatment from a qualified healthcare provider.
The vast majority of users took in BCAA supplements to improve their exercise and muscle-building performance. Many of them were satisfied and reported that their workouts had improved heavily. One user even claimed that BCAAs helped also during the “cutting” phase.
The supplement brand seemed to have no effect on its effectiveness, since some users had tried different brands with similar results.
However, not all users were satisfied. Some reported little or no effects.