Andrews, December 15th, 2008.
What are branched chain amino acids?
Amino acids are the building blocks of protein. Branched chain amino acids
(BCAAs) are so called because of their structure, which includes a “side chain”
of one carbon atom and three hydrogen atoms. There are three BCAAs: leucine,
isoleucine, and valine. Of these, leucine is the most heavily researched, and
appears to offer the biggest physiological benefit. (More on that below.)
For the science geeks, these hydrophobic (water-fearing) amino acids are
referred to as “aliphatic” (from the Greek aleiphar, or oil), as their
central carbon attaches to a branched non-cyclic, open carbon chain.
BCAA structure. Source: University of
BCAAs provide the basis for protein synthesis and energy production (Harper
AE et al 1984; Patti ME et al 1998; Xu G et al 1998; Anthony JC et al 2001). In
fact, BCAAs can comprise up to one-third of muscle protein (Mero 1999). Because
of their prevalence and involvement in protein synthesis and energy production,
BCAAs are important to many metabolic processes.
However, if BCAAs are going to participate in these processes, they must be
available to the body. This means we have to eat enough BCAAs, and at the right
times, to enable such processes to occur.
Why is adequate BCAA intake so important?
The BCAAs are the only amino acids not degraded in the liver. All other amino
acids are regulated by the gut and the liver before being circulated elsewhere
in the body. However, BCAAs head directly into the bloodstream. This means that
dietary intake of BCAAs directly influences plasma levels and concentrations in
muscle tissue (Layman DK 2003). Interestingly, BCAAs are burned for energy
(oxidized) during exercise, so they’re also an important exercise fuel.
Consuming BCAAs before training can increase uptake into muscle tissue
(Mittleman KD et al 1998). This has many benefits:
- BCAA supplementation may lower lactate levels after resistance training and
improve muscular oxidation.
- BCAAs may increase growth hormone (GH) circulation, which may be related to
anabolic mechanisms causing muscle growth (De Palo EF et al 2001).
- BCAA supplementation may decrease serum concentrations of the intramuscular
enzymes creatine kinase and lactate dehydrogenase following prolonged exercise.
This can decrease muscle damage and improve recovery (Coombes JS, McNaughton LR
Muscle is an important site of BCAA activity. There is an increased cell
concentration and breakdown of BCAAs in muscle tissue (Layman DK 2003). BCAAs
are continuously released from the liver and other internal organs to skeletal
muscle so that the BCAAs can assist in maintaining blood sugar levels. Indeed,
BCAAs may be responsible for up to 40% of blood sugar production during exercise
(Ahlborg G et al 1974; Ruberman NB 1975; see also Layman DK 2003).
Glucose production from amino acids. Image from
What you should know
Because BCAAs are so important to muscle tissue, and because they help
maintain blood sugar levels, it’s important to get enough to support your
workouts. Consuming a carbohydrate, protein, and amino acid beverage during and
after training can induce an insulin response, which helps transport BCAAs into
cells. However, availability of leucine is more important than insulin. Within
the muscle cell there’s one particular regulatory pathway for protein synthesis
that’s stimulated by insulin, but dependent on leucine (Anthony et al 2000). In
other words, protein synthesis (and hence muscle rebuilding) depends on how much
leucine is available. And since BCAA levels decline with exercise, it makes
sense to supplement with them during and/or after workouts (Mero 1999).
Because it’s so important to have leucine available for protein synthesis, if
you train in a fasted state, or don’t eat after exercise, you’re going to lose
more protein than you rebuild. However, if you eat adequate BCAAs during this
time, especially leucine, you’ll enhance protein synthesis.
For extra credit
For the body to make new proteins, it needs an estimated daily leucine intake
of between 1 to 4 grams/day (FAO/WHO/UNU 1985). That minimum intake needs to be
met before leucine will be able to impact the insulin signaling pathway. But
that’s just a baseline. Actual metabolic use, especially by athletes and people
doing heavy resistance training, may be upwards of 12 grams/day.
There is a theory that BCAAs can limit central fatigue with endurance
athletes, but it doesn’t appear to be supported by current data.
BCAA content of foods (grams of
amino acids/100 g of protein)
Whey protein isolate 26%
Muscle protein 18%
Soy protein isolate 18%
Wheat protein 15%
Source: USDA Food Composition Tables
Summary and recommendations
BCAAs play an important role in:
- Synthesis of proteins in general
- Glucose homeostasis (i.e. keeping blood sugar levels constant)
- Direct regulation of muscle protein synthesis (via insulin signaling
BCAAs’ potential impact on the aforementioned processes depends upon
availability and dietary intake.
Adequate consumption of BCAAs may help manage body fat, spare muscle mass,
and regulate glucose/insulin balance.
How can you put this knowledge to use?
Try adding BCAAs into your workout drink at a rate of 5 g BCAA per hour of
During periods of lower calorie intake, try adding a BCAA supplement every
2-4 hours during the day.
Anthony JC, et al. Signaling pathways involved in translational control of
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Anthony JC, et al. Orally administered leucine stimulates protein synthesis
in skeletal muscle of postabsorptive rats in association with increased eIF4F
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Ahlborg G, et al. Substrate turnover during prolonged exercise in man. J Clin
Coombes JS, McNaughton LR. Effects of branched-chain amino acid
supplementation on serum creatine kinase and lactate dehydrogenase after
prolonged exercise. J Sports Med Phys Fitness 2000;40:240-246.
De Palo EF, et al. Plasma lactate, GH and GH-binding protein levels in
exercise following BCAA supplementation in athletes. Amino Acids
FAO/WHO/UNU. Energy and protein requirements. Report of joint FAO/WHO/UNU
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Garlick PJ. The role of leucine in the regulation of protein metabolism. J
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Harper AE, et al. Branched-chain amino acid metabolism. Annu Rev Nutr
Layman DK. The role of leucine in weight loss diets and glucose homeostasis.
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Mero A. Leucine supplementation and intensive training. Sports Med
Mittleman KD, et al. Branched chain amino acids prolong exercise during heat
stress in men and women. Med Sci Sports Exerc 1998;30:83-91.
Patti ME, et al. Bidirectional modulation of insulin action by amino acids. J
Clin Invest 1998;101:1519-1529.
Ruberman NB. Muscle amino acid metabolism and gluconeogenesis. Ann Rev Med
Xu G, et al. Branched-chain amino acids are essential in the regulation of
PHAS-I and p70 S6 kinase by pancreatic beta cells. J Biol Chem