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Hey friends,

It's time for another instalment of the Vitamin––the weekly fitness newsletter that helps you be healthier, stronger, and leaner while navigating fitness bullshit.

Do BCAAs live up to the hype?

Branched-chain amino acids (BCAAs) are a popular supplement choice amongst fitness enthusiasts, but how do they stack up against the scientific evidence?

A quick peruse of supplement websites yields a few common claims about BCAA products: They can improve performance, aid in muscle gain, and prevent muscle loss.

On the surface, these claims make sense. Amino acids are the building blocks of muscle (and other bodily proteins), after all.

But what is it about BCAAs specifically that draws so much hype? To understand that, let's quickly talk about amino acids.

There are 20 amino acids which can be split into essential and non-essential.

The 11 non-essential amino acids can be made by the human body, whereas the 9 essential amino acids cannot and thus need to be obtained via the diet.

Of these 9 essential amino acids, three are collectively referred to as branched-chain amino acids: Isoleucine, valine, and leucine.

Leucine is of note since it's built a reputation for being a central player in stimulating the creation of new muscle proteins.

And so, there's at least some mechanistic foundation for why BCAA supplements are so popular: BCAAs contain leucine and leucine triggers the muscle growth process.

It’s important to note, however, that protein sources such as whey or meat contain all 9 essential amino acids. In comparison, BCAAs only contain three of the nine essential amino acids (isoleucine, leucine, and valine).

With this in mind, there are two ways that BCAAs could promote a positive protein balance (i.e. muscle protein synthesis exceeds muscle protein breakdown) and subsequently lead to muscle growth.

The first would be by increasing muscle protein synthesis and the second would be by decreasing muscle protein breakdown.

So, how does the BCAA science stack up? Let's take a look.
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Do BCAAs increase muscle protein synthesis?

Short answer: Most likely, but normal protein sources such as whey and meats do a better job.

Long answer: After a gym session, our muscles are sensitive to the presence of amino acids in our bloodstream. BCAAs have been shown to increase rates of muscle protein synthesis after a weightlifting session. [Jackman SR et al. 2017] [Fuchs CJ et al. 2019]

However, the results of several studies support the notion that eating or drinking an ample amount of high-quality protein (~20g) is sufficient to maximally stimulate muscle protein synthesis.

For example, one study found ingesting 6g of BCAAs produced a similar spike in muscle protein synthesis to 30g of milk protein (also containing 6g of BCAAs), but the effect of the BCAAs was short-lived (0-2 hrs) compared to the milk protein which sustained protein synthesis over a longer time frame (2–5 hrs).

One reason for this could be the complete amino acid profile of milk protein enabled a more robust effect of protein synthesis. But there's also emerging evidence there are other non-protein nutrients in whole foods that enhance the anabolic properties compared to taking a nutrient in isolation (referred to as the food matrix). [Burd et al. 2019]

Taken together, the science so far suggests that BCAAs do influence muscle protein synthesis, but this effect lasts a short time compared to other protein sources with a complete amino acid profile (e.g. whey or lean meats), and the effect of BCAAs is likely drowned out when consuming protein sources containing a full amino acid profile.

Do BCAAs reduce muscle protein breakdown?

Short answer: At rest, most likely. But it's still to be determined whether BCAAs reduce MPB After exercise (where protein breakdown is greater). In any case, whole food sources of carbohydrates and protein likely do a better job than BCAAs.

Long answer: Muscle damage occurs during exercise, and so naturally, muscle protein breakdown is higher in the post-workout window. But, it's unknown whether the relatively modest effect of BCAAs can attenuate the greater amount of protein breakdown after a workout.

Several studies have reported that a mixture of BCAAs can decrease whole-body and muscle protein breakdown. [Louard RJ et al. 1990] [Louard RJ et al. 1995]

However, all these studies were conducted at rest, and no previous study has investigated whether BCAAs decrease protein breakdown after exercise.

That said, while there isn't any direct evidence, we can lean on some indirect evidence to gain some insights into how BCAA supplements compare with whey protein in the post-workout window.

A 2017 study found that supplementing with BCAAs led to a 22% greater increase in MPS than a carbohydrate-only placebo after a resistance training session. [Jackman SR et al. 2017]

However, the magnitude of the increase in MPS was ~50% less than the increase in MPS in previous studies that fed participants whey protein after a bout of resistance training. As the researchers note:

It should be noted that insulin, which is primarily stimulated by the presence of carbohydrates in the blood (but also protein), strongly suppresses muscle protein breakdown.

So, yet again, we have a situation where it seems smarter to have a mixed macronutrient meal (i.e. carbs and protein) to promote muscle growth and suppress muscle protein breakdown around the workout window than just taking a BCAA supplement.

In sum

1. It’s true that BCAAs likely have some mechanistic influence on net protein balance.
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2. But if you're already eating enough daily protein, adding in BCAAs is a bit like throwing a bucket of water into the ocean.
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3. Thus, simply having a meal in the hours before and after a training session will result in a robust protein synthesis response, drowning out any effect of BCAAs.
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4. If dietary protein intake is low, BCAAs could conceivably have a positive effect on muscle building (although it would be better to work on getting adequate protein into the diet in this scenario).
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5. Finally, if, for whatever reason, you still want to supplement with amino acids, you'd be better off supplementing with an EAA (essential amino acid) product that contains all 9 essential amino acids versus a BCAA product that only contains three of the essential amino acids. If there were a hierarchy for protein supplementation, it would be protein > EAA > BCAA.

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