Branched Chain Amino Acids

images-1Branched chain amino acids (BCAAs) are essential amino acids (meaning our body does not create them) that contain an aliphatic (branched) side-chain.

There are three BCAAs: leucine, isoleucine, and valine. These amino acids are key players in the regulation of muscle mass and must be consumed through your diet.

One interesting aspect of BCAAs is their metabolism in the human body. The breakdown of BCAAs is regulated through an enzyme complex known as the branched chain amino acid dehydrogenase complex, which we are going to shorten to something more manageable and call it BDC.

To take biochemistry from test tube to muscles, this means that when we have higher levels of BDC around, more BCAAs are broken down.

Levels of BDC in the human body are increased when we exercise, indicating that exercise promotes breakdown of BCAAs.

Another important aspect of this complex (which we will discuss later in this article) is that when the metabolites of BCAAs are present (i.e. the products of the breakdown), they inhibit the BDC complex. Which means if you have a lot of BCAA breakdown products around you preserve the currently available amino acids.


Before we dive into the individual BCAAs and their functions, we need to cover one aspect of the collective group of BCAAs, their proposed ability to reduce fatigue.

There is a hypothesis about fatigue during training, it is called the central hypothesis of fatigue.

The Central Hypothesis of Fatigue states that elevated levels of serotonin in the brain caused by increased levels of tryptophan (tryptophan is converted to serotonin) during exercise induces fatigue.

BCAAs are thought to prevent this because they compete for the same transporter into the brain. So the hypothesis is that if you increase your BCAAs in the blood by supplementation, you prevent tryptophan uptake and thus reduce fatigue.

Now this sounds great as a biochemical and physiological theory. . . but unfortunately the research hasn’t created any promising results and any anti-fatigue effects of BCAAs by reducing “Central Fatigue” appear to be minimal if any.


Valine is the least researched or well understood of the 3 BCAAs, and as such the currently known biological effects of it are minimal.

Valine is a glucogenic amino acid, meaning it can create and/or be converted into glucose1,2. The methyl carbons of valine can be utilized to produce glucose and ultimately glycogen.

This process of valine oxidation for glucose is increased in skeletal muscle following injury, which suggests that consuming extra valine in times of muscle injury (i.e. heavy training) might be beneficial for muscle recovery. Unfortunately for valine, it is far less effective at this than Leucine (a theme that repeats itself).


The main reason people use BCAAs is to optimize muscle building, and in the land of BCAAs, leucine is the king of promoting muscle protein synthesis.

When we think of the science behind muscle protein synthesis we think of two proteins, mTOR and S6K.

Interestingly, leucine is able to activate the mTOR pathway independently of other growth signals, like insulin.

Leucine is a major contributor to the anabolic capabilities of protein supplementation by activating mTOR. For example, 5g of leucine elicits a greater muscle protein synthesis signal than 5g of a mixture of BCAAs.

There is even evidence that leucine provides the most potent growth signal when you compare leucine to other amino acids and even insulin!

Do you get it yet? Leucine is probably pretty important for muscle protein synthesis.


Just in case you don’t really care about growing muscle (which if you don’t, I am sorry for your loss), leucine might also help with recovery.

One of the critical components of recovery is how quickly you can replenish your glycogen stores. For hard-charging athletes the mantra is “the faster the better”. The quicker one can reload their glycogen stores, the faster they are able to recover. Leucine can actually speed up the recovery process by increasing glucose uptake. It does this with a nifty little trick.

Leucine signals for insulin to be release from the pancreas without the presence of carbohydrate. Working in conjunction with insulin, leucine can actually have a positive two-fold effect on glucose uptake into muscle cells.

Combining leucine supplementation with post-workout carbohydrate has been shown to be incredibly effective in restoring muscle glycogen, more so than amino acid or carbohydrate supplementation alone. Interestingly enough, insulin also works synergistically to control muscle protein synthesis in response to diet and training. When it comes down to recovery and muscle growth, leucine is critical for optimizing both!