Branched Chain Amino Acids vs Essential Amino Acids
What Are Amino Acids?
Amino acids are the building blocks of protein are the catalyst for almost every chemical process in the body. Most people associate amino acids purely with protein synthesis and muscle gain, but they’re also necessary for nearly every other physiological function, including enzyme production, hormone regulation, cognitive ability, neurotransmitter balance, and metabolism. There are 20 amino acids in total, and all of them are required to make these vital processes happen.
The protein we eat in our food is broken down into these 20 different amino acids. Not only do these amino acids contribute to the physical structure of our bodies, but they also provide energy. Only about 10% of the protein we digest goes towards muscle building and repair. 50% of it goes towards the liver and GI tract and 40% is used for energy production, formation of neurotransmitters, and supporting proper detoxification and elimination.
Essential Amino Acids
Of the 20 amino acids, 9 are classified as essential which means that the body doesn’t produce them itself and they need to be obtained via diet.
Methionine: helps the body process and eliminate fat, promotes cardiovascular health, supports liver function, and helps the body eliminate toxins. Methionine also plays a role in the production and regulation of the most potent antioxidant in your body, glutathione.
Lysine: plays a role in the secretion of growth hormone, which helps to support muscle repair and recovery. It’s also an essential part of structural proteins (collagen and elastin) which are important in skin and connective tissue. Lysine may also help with the release of growth hormone which impacts muscle repair and recovery.
Phenylalanine: has a pain reduction and antidepressant effect and is necessary for the synthesis of the neurotransmitters dopamine and norepinepherine (two “feel good” neurotransmitters). Increasing these neurotransmitters may play a role in lowering your rate of perceived exertion during exercise. It also plays a role in the release of adrenaline and noradrenaline which play important roles in the function of your nervous system.
Threonine: supports the metabolism of fat and is important in immune function. It’s also a critical component of structural proteins and connective tissue. Theonine also plays a role in digestive health and restful sleep.
Tryptophan: a precursor for serotonin which regulates sleep, appetite, and mood. Serotonin also has pain reducing qualities and can increase pain tolerance during workouts. Tryptophan is also required to make vitamin B3 (niacin) which helps to regulate blood sugar and helps to prevent cholesterol from building up where you don’t want it.
Leucine: critical for protein synthesis, blood sugar regulation, and growth hormone production.
Isoleucine: helps to prevent muscle breakdown during exercise, possibly leading to faster recovery times. It also plays a role in immune function, hemoglobin production, and energy regulation.
Valine: helps to stimulate muscle regeneration, helps to prevent muscle breakdown during exercise, and plays a role in energy production. Valine may help you recover faster because you’ll have less muscle damage. It also plays a role in regulating blood sugar levels.
Histadine: Histadine’s status as an essential amino acid is questionable since it is easily produced in the presence of other essential amino acids. It’s a precursor to histamine which helps to fight off the free radicals you produce during exercise. It is also a precursor to carnosine, which helps to turn lactic acid back into useable fuel and decrease soreness.
Branched Chain Amino Acids
The three branched chain amino acids (BCAAs) are Leucine, Isoleucine, and Valine. Unlike all the other amino acids, their physical structure is branched.
Because of their branched structure, BCAAs are metabolized in the muscles instead of the liver which means that they are available quickly after ingestion and can be used as energy during exercise. BCAAs have been shown to increase muscle mass, decrease fatigue, and improve glycogen storage.
The problems with BCAAs
A meta-analysis of data through 2017 showed no human studies in which BCAAs were solely responsible for more efficient protein synthesis or being beneficial to athletic performance.
This analysis found two studies where BCAAs actually decreased muscle and protein synthesis and increased the rate at which lean tissue was catabolized (broken down). This means that muscle tissue was being broken down more quickly than it could be repaired. The reason that this happened was that the body was trying to create the other essential amino acids from the three BCAAs in order to complete protein synthesis.
In other words, BCAAs are not beneficial in isolation. All of the essential amino acids are needed to complete protein synthesis.
This study came to the conclusion that BCAAs are ineffective for muscle building or increasing recovery rates.
There are other negative effects of BCAAs on overall health:
High doses of BCAAs can deplete B vitamins. Vitamin B6 is needed to produce an enzyme called Branched Chain Keto Acid Dehydrogenase which is necessary to break down and utilize BCAAs. Another enzyme that’s needed to metabolize BCAAs uses four other B vitamins - B1, B2, B3, and B5. These vitamins are the limiting factor in BCAA metabolism. So if you’re taking large doses of BCAAs, you’ll need to be aware of your B vitamin status.
Too many BCAAs can have a negative effect on serotonin production. BCAAs and tryptophan goth use the same carrier system to get to the brain which means that too many BCAAs in the absence of other amino acids disrupts the uptake of tryptophan and causes a shortage of serotonin. Low serotonin contributes to depression, anxiety, sleep issues, etc.
BCAAs may cause insulin resistance and can interfere with the regulation of blood glucose.
mTOR and Leucine
One of the reasons why BCAAs are so loved in addition to being quick workout fuel is that they activate something called the mTOR pathway which stimulates muscle protein synthesis.
Much of the activation of mTOR comes from the amino acid leucine, so some people assume that leucine supplementation alone is better than BCAAs or essential amino acids. However that’s not usually good enough and has the potential for some negative consequences at high doses.
Much of the hype around BCAAs, as we’ve already talked about was that they increased muscle synthesis (through the activation of the mTOR pathway), however in order to increase your protein synthesis above basal levels, you need all NINE essential amino acids.
BCAAs are anti-catabolic, so they prevent the breakdown of muscle and protein, but they are not necessarily directly anabolic, so they don’t directly help you build muscle or increase protein synthesis. 
In order to build muscle, your muscle protein synthesis needs to be greater than the rate of muscle protein breakdown. Since BCAAs don’t contain all of the EAAs that are needed by the body to build muscle, they don’t actually directly aid in muscle growth.
Why Choose EAAs Over BCAAs
Despite all the potential issues with BCAAs, they are still necessary for overall health and do actually serve as a quick source of fuel during workouts. But they don’t build muscle without further help.
You need adequate amounts of all the essential amino acids in order to optimize your health - including protein synthesis.  BCAAs can begin the process, but the other six EAAs are needed to complete the process.
EAAs have other health benefits:
EAAs preserve muscle tissue, especially when you train in a fasted state.  They help to decrease indicators of muscle damage and help promote a healthy inflammatory response.
EAAs post-workout increases muscle protein synthesis which may help speed recovery and decrease fatigue post-training. 
EAAs activate the brain cells that regulate hunger and satiety and may help normalize appetite. 
Supplementation with amino acids have been shown to improve sleep and mood and can help decrease symptoms of depression. 
When you compare EAAs to BCAAs, EAAs stimulate a stronger anabolic response. One study determined that BCAAs stimulated a 22% greater muscle protein synthesis following resistance exercise when compared with a placebo, but this increased response was about 50% less than the MPS response to a dose of whey protein that contained a similar amount of BCAA. 
So BCAAs are better than consuming nothing during your workout, they are not as effective as whey protein, likely due to the lack of other EAAs. This means that lack of sufficient EAAs limit the response of MPS.
Also, most of this research is directly applicable to strength training and not specifically endurance training. But all athletes should be doing some kind of strength training even if the goal is not necessarily to build muscle. Though for some endurance athletes, like triathletes, there is a balance to be had between big strong muscles and being lean and light.
It’s also important to remember that most (if not all) research was done in men. Which doesn’t mean that it doesn’t apply to women, but as Stacy Sims says, “women are not small men.”
Amino Acid Supplementation Timing
Is it better to take your amino acids before you workout so they are in your system and can get to work while you’re training, or is it better to wait until after for more rapid uptake by your muscles?
One study sheds some light on this problem. Men were assigned to either a pre-workout dose of EAAs or post workout EAA dose. After an intense leg session, muscle biopsies were collected to determine the difference between update of EAAs pre vs. post workout.
The men who consumed EAAs pre workout had 42% uptake vs. the post group who only took up about 16%. 
It’s important to note that this was a VERY small study (only 6 participants), but they used a crossover design (all individuals did both) so it does compare both sides, which makes the evidence stronger.
If you’re a die-hard BCAA fan, you might want to consider switching to EAAs as your BCAAs may not be doing you any favors. If you don’t use BCAAs or EAAs, you might consider adding some EAAs to your pre-workout routine. There is not a lot of evidence regarding the direct benefits of EAAs for endurance athletes, but at the very least they are important in preventing muscle breakdown and muscle synthesis.