Branched Chain Amino Acids

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).

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.

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what effects branched chain amino acids has on your body, and how strong these effects are.

Grade	Level of Evidence [show legend]
	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.	Notes
	Aerobic Exercise	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
	Fat Oxidation	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.
	Fatigue	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
	Lactate Production	-	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
	Ammonia	Minor	- 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
	Processing Accuracy	Minor	- See study	The increased processing accuracy appears to be secondary to reducing exercise-related fatigue, and occurs when testing is after exercise.
	Rate of Perceived Exertion	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
	Reaction Time	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
	Weight Loss	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
	Adrenaline	-	- See study	No significant influence on adrenaline concentrations
	Anaerobic Running Capacity	-	- See study	No significant performance enhancing effect on short-term cardiovascular exercise
	Blood Glucose	-	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)
	Cortisol	-	- See study	No significant interactions with BCAA supplementation and cortisol
	Dopamine	-	- See study	Similar to the other catecholamines (adrenaline and noradrenaline), serum dopamine does not appear to be altered with supplemental BCAAs.
	Heart Rate	-	Very High See 2 studies	No significant alterations in heart rate noted with BCAA supplementation at rest or during exercise
	Insulin	-	- See study	No significant influence of BCAA supplementation on fasting insulin levels
	Ketone Bodies	-	- 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
	Muscle Soreness	-	Moderate See 2 studies	No significant influence on muscle soreness when assessed 2-3 days after exercise that is preloaded with BCAA supplementation
	Noradrenaline	-	- See study	BCAA supplementation does not appear to significantly influence noradrenaline concentrations in serum
	Oxygen Uptake	-	- See study	Oxygen uptake during anaerobic cardiovascular exercise does not appear to be modified with BCAA supplementation
	Power Output	-	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]