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Branched chain amino acids are essential amino acids (meaning you have to get them from your food—your body can’t make them). They include leucine, isoleucine, and valine. They’re best known as a supplement for body builders looking to maximize the effect of their workouts. 

Here’s how they help with that, a few other benefits besides—and a few caveats, too. 

BCAAs for Muscle Growth and Recovery

Branched chain amino acids do indeed stimulate protein synthesis and inhibit protein degradation—and muscle is made out of protein. 

They do this by stimulating the mammalian target of rapamycin (mTOR), which promotes use of glucose, breakdown of fatty acids, and production of mitochondria. 

BCAAs also decrease exercise fatigue. It’s speculated that this is because ingestion of BCAAs compete with tryptophan as it crosses the blood brain barrier during a hard workout—and as anyone who has ever consumed a big turkey dinner knows, tryptophan can make you tired. 

BCAAs even decrease muscle soreness after hard workouts, because they decrease muscle breakdown—which means less lactic acid. 

While studies vary a bit, the effects are similar between specific BCAA supplementation and whey protein supplementation (which contains BCAAs as well as other amino acids too). 

BCAAs and Insulin Resistance

As mentioned above, in addition to building muscle, BCAAs also promote the use of glucose. As expected, this means that BCAAs decrease circulating levels of glucose. Specifically leucine has been shown to improve glycemic control in both animals and humans. 

They do this by inducing the pancreas to release more insulin. This is similar to the mechanism of action of the wildly popular Ozempic/semaglutide. 

One concern regarding this mechanism of action, though: insulin resistance occurs with a prolonged feedback system, in which high circulating glucose stimulates the pancreas to release ever increasing amounts of insulin in order to deal with it. Eventually, the cells become desensitized to the constant signal of insulin, telling them to take up more glucose—and the cells require an ever higher amount of insulin to elicit the same response. 

While this study suggests that BCAA supplementation doesn’t worsen already existing insulin resistance, other studies suggest otherwise.

Specifically in the context of a high fat diet, it appears that BCAAs do, in fact, worsen insulin resistance.

BCAAs for Weight Loss

Since BCAAs seem to encourage the body to burn its various sources of energy as fuel, it makes sense that they would lead to actual weight loss too (as long as not consumed along with a high fat diet, as mentioned above). 

This study shows that they do, in fact, decrease visceral fat (the most dangerous kind, from a cardiovascular standpoint). 

I suspect that largely, whether BCAAs help or hurt weight and insulin resistance all depends upon the context in which one uses them. A marathon runner who takes BCAAs to optimize energy usage isn’t likely to have a problem with insulin resistance as a result of BCAAs. On the other hand, a sedentary individual with high glucose levels and insulin resistance already might be a different story. While BCAAs will trigger a greater release of insulin, which will encourage the body to take up the glucose the person has just consumed and take it into the cells, if they’re not burning that energy, it will still have to get stored. This might make the problem worse in the long run. 

There’s no totally free lunch, unfortunately. 

Concerns about BCAAs

Aside from the caveat above, there’s one possible philosophical concern with BCAAs, and it goes back to mTOR. 

I wrote here on the interesting see-saw between growth and longevity—and the fact that your body can prioritize one or the other, but not both at any given time. 

Since leucine in particular seems to stimulate growth, it simultaneously shuts down autophagy (or the process of breaking down and recycling senescent cells)—a critical process for longevity. At certain times in our lives, it’s appropriate to prioritize one over the other, and of course we can’t be in autophagy all the time. 

As with everything else, balance is the key.