Review: BCAAs (Branched Chain Amino Acids): Do BCAAs Build Muscle?

Review: BCAAs (Branched Chain Amino Acids): Do BCAAs Build Muscle?

The branched chain amino acids—leucine, isoleucine and valine—form an important subclass of essential amino acids widely used as bodybuilding supplements.

What are amino acids?

Amino acids are the “building blocks” of proteins. Every protein in the human body is made up of a chain of amino acids, bonded together, and folded into a 3 dimensional shape. All amino acids have the same, basic “skeleton”—where they differ is in the chemical groups—or side chains – that are attached to each one. Each side chain interacts chemically with water; and it is these interactions which drive protein folding, and determine the final shape – and function – of the protein.

What About Branched Chain Aminos?

Branched chain amino acids are so called, because the side chain of each one has a “forked” structure, featuring two terminal methyl (–CH3) groups.

The BCAAs—and leucine in particular—have multiple functions that make them useful for anyone engaged in strenuous exercise. Leucine, isoleucine and valine…

  • are important components of body proteins and precursors to non-protein compounds
  • stimulate the process of muscle protein synthesis (MPS)
  • reduce muscle protein breakdown (catabolism)
  • may reduce fatigue, due to effects on the central nervous system

A brief review underscores just how critical BCAAs are, when it comes to maintaining and building muscle mass.

BCAAs and body proteins/non-protein compounds

It’s been estimated that BCAAs account for 35%–40% of the essential amino acids in body proteins and make up about 14% of skeletal muscle. In addition, BCAAs are needed for the synthesis of the non-essential amino acids, glutamic acid, glutamine and alanine, which have vital protein and non-protein functions in their own right.

Cholesterol is also one of the by-products of leucine metabolism…this may not seem like a good thing, as cholesterol is associated with cardiovascular disease. The reality, however, is that some cholesterol is essential for health: it’s an important component of cell membranes, and is necessary for the synthesis of steroid hormones—including testosterone.

Thus, an adequate supply of dietary BCAAs is necessary to maintain basic physiological processes essential to general health and well-being.

BCAAs and muscle protein synthesis (MPS)

The BCAA leucine also serves an important function as an initiator of muscle protein synthesis.

Stimulation of MPS by leucine is extremely complicated, and involves both insulin-dependent and independent pathways.

In brief, leucine can induce insulin release directly, as well as through enzymatic activation. Insulin, in turn, activates specific elements needed for the production of proteins from mRNA (aka, translation).

In addition, leucine can enhance MPS through direct activation of specific translational elements, or through inhibition of a translational inhibitor (AMPK).

So does more leucine mean more muscle? No…it’s not quite that simple. By itself, leucine stimulation of MPS is short-lived, and returns to baseline within a couple of hours, despite continued availability. Exercise, however, provides an additional, and synergistic stimulus, that can persist for up to 48 hours afterwards. This underscores the need for an adequate supply of leucine and other essential amino acids to capitalize on the effects of exercise on muscle growth.

BCAAs and muscle protein catabolism

Exercise induces the breakdown of BCAAs by increasing the activity of Branched Chain Alpha-Keto Acid Dehydrogenase (BCKDH). This enzyme is part of a complex that’s responsible for removing the amino nitrogen groups (deamination), and converting the resulting carbon skeletons to compounds that can be utilzed for energy. Aerobic exercise, for example, can reduce plasma leucine by 11% – 33%, while strength exercise reduces leucine by approx. 30%. This breakdown is enhanced when muscle glycogen is low.

In the absence of supplemental BCAAs, this process occurs at the expense of skeletal muscle, and can have the effect of “cancelling out” the exercise-induced increase in MPS.

It’s been demonstrated that supplemental BCAAs can reduce the breakdown of skeletal muscle during exercise, and possibly attenuate related problems, such as delayed onset of muscle soreness (DOMS).

BCAAs and fatigue

If the above isn’t enough, exercise-induced depletion of BCAAs may also contribute to central fatigue by allowing more tryptophan to cross the blood brain barrier. Tryptophan is the precursor for neurotransmitter 5-hydroxytryptamine (5-HT or serotonin), which influences mood and wakefulness. Increases in brain 5-HT are associated with fatigue during sustained exercise. Both tryptophan and BCAAs are classified as “large, neutral amino acids” (LNAAs) and compete for the same transporters. When plasma BCAAs are raised, less tryptophan can cross and be converted to 5-HT.

It should be obvious by now, that BCAAs are essential to anyone interested in building muscle. What is less obvious is whether or not supplementation is actually needed in order to achieve all of the benefits. Why not just eat BCAAs in the form of food?

Looking over the available evidence, I think a case can be made for modest supplementation.. For example, one study demonstrated that coingestion of leucine + protein + carbohydrate was more effective than either carbohydrate alone or carbohydrate + protein for increasing insulin and MPS, and decreasing protein breakdown.

An earlier study also demonstrated benefits for athletes consuming 1.26 mg/kg protein and 50 mg/kg leucine per day, over 5 weeks of strength and speed training. If your intake of high quality protein isn’t all it could be, then supplementation may not be a bad idea.

Attenuation of DOMS and improved recovery is another possible benefit. Although the research on this is limited, many trainees have reported improvement in post-workout soreness after supplementing with BCAAs.

BCAA supplementation also may have something to offer to older trainees. Aging is associated with decreased sensitivity of MPS to feeding. Nonetheless, severall studies have shown that direct supplementation with either leucine, or a mixture of amino acids containing a high proportion of leucine, can offset this disadvantage.

Various authors have also recommended BCAA supplementation during cutting phases, where the risk of muscle loss is more acute. Since BCAAs help with nitrogen retention in a variety of catabolic states, it seems like a reasonable precaution.

It does not need to be overdone, however. Most bodybuilders already consume a fair amount of high quality protein, in the form of meat, fish, poultry, eggs, dairy products, and supplements such as whey protein or casein. All of these are rich sources of BCAAs.

In addition, consuming whole food sources of BCAAs makes more nutritional sense, as they contain additional vitamins, minerals and other nutrients useful for health and muscle growth. Food is still more important than supplements, when it comes to muscle growth.

Products containing free form BCAAs include:

AST BCAA 4500; PrimaForce BCAA; Optimum BCAA 1000 Caps; Ultimate Nutrition Branched Chain Amino Acids; SciFit BCAA Powder 5000; Beverly International Glutamine Select Plus BCAAs; Dymatize BCAA Complex; Iron Tek Essential BCAA; Met-Rx BCAA 2000; among many others.

Branched Chain Aminos are available at!

Author: elissa

Elissa is a former research associate with the University of California at Davis, and the author/co-author of over a dozen articles published in scientific journals. Currently a freelance writer and researcher, Elissa brings her multidisciplinary education and training to her writing on nutrition and supplements.

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