Updated: Nov 23, 2020
Branched Chain Amino Acids (BCAA) have been very popular among different kinds of sport athletes looking to gain both strength and size. However, the BCAA name has been taking some flak lately. this is partly because the people taking them are simply just not getting the results they expect, and partly because of a response to a recent critical review of them. This was done in an article published by the author, Robert Wolfe in the journal of the International Society of Sports Nutrition. In this article, Wolfe argues for the lack of efficacy of BCAAs to boost muscle protein synthesis and increase muscle growth. Wolfe does some excellent points in the review. These go deep into the biochemistry of protein, and he makes a strong case against BCAA as a dietary supplement to enhance growth of muscle tissue.
Today, However, we are going to skip most of the biochemical and physiological nuance and point our attention straight to the elephant in the room: Have you ever seen anyone get massive from taking BCAA? Not exactly, right? there are a couple of big reasons for this which we'll cover here.
The on-going Battle Between BCAA and EAA
Let's bring the current BCAA vs EAA debate a litle more into context here. This will help review the actual difference between BCAA and EAA in general. The essential amino acids (EAA) are a group of nine amino acids that one needs to obtain from the diet, hence the name "essential". They're essential because the body is not capable of synthesizing them on its' own. In order to synthesize new protein in muscle or anywhere else in the body for that matter, only the EAAs are required. This is because the other - non-essential - amino acids can be synthesized as needed. Three constituents of EAAs are called L-Leucine, L-Isoleucine and L-Valine. These are also known as the BCAAs due to the shape of their branched carbon side-chains. So technically, if we take in BCAA, we are in fact also taking in EAA at the same time, just not all of them. Since any given protein consists of (more or less) the full complement of 20 essential and non-essential amino acids, and EAAs need to come from the diet, EAA availability (not BCAA availability) is the limiting factor for MPS (muscle protein synthesis) at any given time.
Did you get that noted down? No? Alright. Here's the same thing said in short: all of the EAAs are an absolute requirement for protein synthesis. What does this mean? You're right. If we only take in BCAA, we are missing the rest of the EAAs and thus do not have the full spectrum. So, only taking in BCAA means no protein synthesis. Simple, right? So why would we even consider to just take BCAA?
The "case" for BCAA
Muscles are constantly making and breaking down protein. It's called muscle protein synthesis (MPS) when they are making protein, and muscle protein breakdown (MPB) when they're breaking down protein. In muscle at steady-state (if its not growing or shrinking), rates of MPB and MPS are approximately even. That's why anything that is capable of shifting the balance between MPB and MPS away from MPB, and towards MPS, should result in increase muscle growth.
BCAAs are some of the first amino acids to be liberated from muscle tissue that's been brown down. This is why the original idea behind taking in BCAA while training was that increased levels of BCAA in the blood might have "tricked" the body into thinking that no more protein breakdown was needed in muscle tissue, thus sparing muscle proteins. There is actually also quite a bit of evidence that supports this very idea. It has been well-demonstrated that BCAA has been shown to decrease muscle soreness. The second argument for the use of BCAA is based on the effects of L-Leucine on anabolic signaling. This amino acid in particular has a powerful activating effect on the machinery inside cells that control protein synthesis. In other words, L-Leucine is very good at turning on the button for protein synthesis. This has been demonstrated in pretty much every single experimental model that has been tested in including cultured rats and people.
The "case" against BCAA
Alright. So; BCAAs suppress MPB and activate anabolic signalling. Sounds pretty good for muscle growth, doesn't it? But why does no one seem to be getting much of results then? There must be something missing here, right? Maybe it's because decreased muscle protein breakdown and increased anabolic signaling activity don't always don't mean muscle growth? Both have been measured and published in studies for years, and this type of research was often used by supplement companies to market BCAA sales on the labels of products. It's possible for muscle protein breakdown to decrease (which is good, right?) as well as anabolic signaling to increase (also very good) without making one single new muscle protein for two very important reasons:
1) By reducing muscle protein breakdown, BCAA - when taken alone - can actually limit muscle protein synthesis
This sounds crazy, right? If muscle protein synthesis was held constant and muscle protein breakdown was decreased, the result would of course be more muscle growth, but in all actuality, the situation is not quite that simple. Muscle protein synthesis is partly dependent on muscle protein breakdown. It is generally known and accepted that intense weight training causes damage to muscle proteins. It it necessary for these very proteins to be broken down and replaced in order for both growth and repair to take place. Some of the amino acids that come from broken down muscle tissue get sent to the liver and turned into glucose (sugar molecules) to make sure the body can keep up with the demand for energy that is put upon it during weight training.
Some also get used in a recycling process in which they are turned into individual amino acids that can be used for new protein synthesis. Now, the reality is that protein turnover (for example muscle protein breakdown and amino acid recycling for new protein synthesis) has to occur for muscle growth to happen. Yes, a lot of sacred cows has been slain here so to say, because the conventional idea is that we need to suppress muscle protein breakdown as much as possible for new muscle tissue to grow. This is true when we're talking about longer periods of time, but when considering it on the shorter time-scale (during training and approximately 24 hours afterwards), protein needs to turn over (muscle protein breakdown has to occur, essentially). This is the reason why those BCAAs could be held responsible for growth of muscle tissue. When BCAA is taken alone, during or after training, the full spectrum of essential amino acids (EAA) is not available for new protein synthesis, and this is where EAA makes for a far better choice.
Hook this argument up with the fact that BCAA has the ability to suppress muscle protein breakdown and recycling of amino acids, and it could result in a paradoxical decrease of muscle protein synthesis (or less at least). No, of course not: BCAA does not shut down muscle protein breakdown completely; they only have subtle suppressive effect. Then, the result is a subtle decrease in the amount of essential amino acids that get recycled from damaged muscle protein and overall reduced muscle protein breakdown rates (relative to what would have occurred had more essential amino acids been available, that is).
Alright, BCAA has pretty much taken a beating of the ages here, but it is absolutely crucial to keep in ind that this new age view of EAA vs. BCAA does indeed exist in shades of light and dark grey rather than plain black and white. Kevin D. Tipton's (PhD at the University of Stirling) Exercise and Nutrition Research Group recently published a paper in the Journal Frontiers in Physiology in which they demonstrated that BCAAs do in fact stimulate muscle protein synthesis after resistance training in human test subjects.
If you're saying that this should be no surprise, you're absolutely right, since (as mentioned above) BCAAs do not completely suppress muscle protein breakdown. There would be some protein that had been turned over in this study to liberate the additional EAAs for muscle protein synthesis required. However, this does not suggest that taking in BCAA as a dietary supplement is ideal; only that they "work a little bit".
2) More anabolic signaling does not always mean to more protein synthesis
There are a lot of papers that have been published on L-Leucine and BCAA that have indeed shown and increased anabolic signaling. The problem is just that there is often times a disconnect between the activation of anabolic signaling pathways and actual protein synthesis in the muscle tissue - reference to point no. 1 above for this to become clearer. If the suppression of muscle protein breakdown caused by BCAA before, during and after training also somewhat suffocates protein synthesis after training, then the result that BCAA at times can activate anabolic signaling without an increase in muscle protein synthesis, all of a sudden makes sense.
When a cell absorbs L-Leucine, a number of anabolic signaling pathways will be activated including mTOR, which is the master-regulator of protein synthesis. The question is, though: what happens when anabolic signaling is activated while the full spectrum of essential amino acids is not available for muscle protein synthesis? Muscle protein synthesis doesn't happen - or at least there is less - in spite of all that anabolic cell signaling. Taking in BCAA alone is like putting a key into the lock on a door, expecting it to open, without actually turning the key.
Daniel Emil Ussing