By Dr. Mercola
When your body breaks down or digests proteins, amino acids are what's left behind. There are nine essential amino acids, which are not made by your body and therefore must be obtained via your diet.
Of them, three — leucine, isoleucine and valine — are considered branched-chain amino acids (BCAA) because they have a branched molecular structure.
While most amino acids are broken down in your liver, BCAAs are broken down primarily in your muscle. As such, they're believed to help improve exercise performance as well as reduce the breakdown of muscle.
Supplemental BCAA is popular among athletes and body builders; however, I'd caution against taking BCAA in supplement form because it can activate the mTOR pathway, an ancient molecular signaling pathway. It's best to obtain BCAAs from your diet.
Benefits of Branched-Chain Amino Acids for Exercise Performance
There are a number of reasons why BCAAs are important. In general, they act as building blocks for protein and muscle and may also help to regulate your blood sugar levels and even improve blood-sugar metabolism.1
They've received quite a bit of attention as of late for their potential to reduce fatigue during exercise, as well.
Earlier this year, a study published in the Journal of Sports Science and Medicine (JSSM) revealed that BCAAs improved endurance exercise performance among endurance runners, possibly by inhibiting the brain's production of serotonin (elevated cerebral serotonin is one factor that contributes to fatigue during exercise, and serotonin is associated with feelings of lethargy and tiredness).2
BCAAs alleviated central fatigue among the runners during two consecutive days of competitive races, allowing them to run faster with the same degree of perceived exertion. This led the researchers to suggest BCAA may be especially helpful for athletes facing multi-day competitions.
Other research suggests BCAAs may lower ratings of perceived exertion during exercise by 7 percent and ratings of mental fatigue by 15 percent compared to placebo.3 Even among sailors taking part in a 32-hour offshore sailing race, a high-protein diet with BCAAs decreased the feeling of fatigue.4
How BCAAs Reduce Muscle Soreness
BCAAs' other claim to fame is their ability to reduce muscle soreness after a workout, and they're known to increase protein synthesis and decrease muscle protein breakdown.5
BCAAs taken before and following damaging resistance exercise was shown to reduce markers of muscle damage as well as accelerate recovery. According to the Journal of the International Society of Sports Nutrition (JISSN):6
"It seems likely that BCAA provided greater bioavailablity of substrate to improve protein synthesis and thereby the extent of secondary muscle damage associated with strenuous resistance exercise."
BCAAs are also known to lower levels of creatine kinase and lactate dehydrogenase, which are enzymes associated with muscle damage, and therefore to reduce the muscle damage associated with endurance exercise.7
When taken prior to squat exercises, female exercisers experienced significantly lower levels of delayed-onset muscle soreness (DOMS).8
In addition, an animal study found BCAAs, in particular leucine, "accelerate recovery from muscle damage by preventing excessive inflammation."9 While there is some conflicting data, BCAAs do seem to help reduce muscle soreness following exercise. According to Authority Nutrition:10
"Various studies asked participants to rate their muscle soreness levels after performing certain strength-training exercises. Participants who were given BCAA supplements rated their muscle soreness levels as much as 33 [percent] lower than those given a placebo.
In some cases, those given BCAAs also performed up to 20 [percent] better when they repeated the same strength-training tests 24 [to] 48 hours later. However, effects may vary based on your gender or the total protein content of your diet."
Do BCAAs Help Build Muscle?
Body builders may supplement with BCAAs because they're believed to enhance muscle growth while decreasing the rate of muscle breakdown. Leucine, in particular, is most known for its role in muscle building.11 As reported in the Journal of Nutrition:12
"It has been reported that BCAA supplementation before exercise attenuates the breakdown of muscle proteins during exercise in humans and that leucine strongly promotes protein synthesis in skeletal muscle in humans and rats, suggesting that a BCAA supplement may attenuate muscle damage induced by exercise and promote recovery from the damage."
" … [T]he BCAAs … leucine and valine caused a significant suppression in the loss of body weight in mice bearing a cachexia-inducing tumour (MAC16), producing a significant increase in skeletal muscle wet weight, through an increase in protein synthesis and a decrease in degradation."
It should be noted, however, that BCAAs play a role in a number of metabolic pathways and also act as regulators of certain cell signaling pathways. As a result, they may also influence diseases like diabetes and cancer, although their exact role is only beginning to be uncovered.
In the case of diabetes, for example, BCAAs have been found to both decrease blood sugar levels and raise them depending on the circumstances.
As mentioned, this is one reason why I do not recommend taking BCAAs in supplement form but instead recommend increasing our intake via dietary sources. For instance, the journal Metabolites explained the complex role of BCAAs in diabetes and cancer:15
"An elevation in branched-chain amino acids has recently been shown to be significantly correlated with insulin resistance and the future development of diabetes. In cancer, the normal demands for BCAAs are complicated by the conflicting needs of the tumor and the host.
The severe muscle wasting syndrome experience by many cancer patients, known as cachexia, has motivated the use of BCAA supplementation. The desired improvement in muscle mass must be balanced by the need to avoid providing materials for tumor proliferation."
Weight Loss, Liver Disease and Other BCAA Effects
BCAAs are widely used in people with liver disease to help preserve and restore muscle mass as well as improve hepatic encephalopathy, which is a complication of liver disease that can lead to confusion, loss of consciousness and coma.16
Further, BCAAs are known to improve nutritional status, prognosis and quality of life in people with chronic liver disease.17 BCAAs may also enhance weight and fat loss. A higher intake of BCAAs is associated with a lower likelihood of becoming overweight or obese among middle-aged adults.18
In one study of wrestlers, BCAA supplementation along with a low-calorie diet also reduced more body fat than calorie restriction alone,19 and they've been found to be inversely associated with abdominal obesity as well.20 Authority Nutrition summed it up by saying, "BCAAs may help prevent weight gain and enhance weight loss. However, more research is needed to determine whether supplements provide any added benefits over a high-protein diet."21
Why You're Better Off Getting BCAAs From Food, Not Supplements
One of the primary problems with BCAA supplements is that excess amino acids stimulate mTOR. Insulin, leptin and insulin-like growth factor (IGF) are examples of nutrient-sensing hormones that in turn regulate metabolism, growth, cell differentiation and cellular survival. Organizing all of these nutrient sensors is the mammalian target of rapamycin (mTOR).
It decides whether cells should replicate now or stay alive to replicate at a more opportune time in the future when nutrients are more plentiful. The latter is part of the mechanism that allows for life extension.
The mTOR pathway regulates growth and repair. Either growth or maintenance and repair is promoted, depending on whether mTOR is up- or downregulated. When mTOR is suppressed, maintenance and repair is upregulated and that results in increased longevity, which is what you want.
However, excess amino acids stimulate mTOR, which is why I don't recommend BCAA supplementation (or eating large amounts of protein). Of all the components that stimulate mTOR, amino acids are the most potent stimulators.
Virtually all cancers are associated with mTOR activation, as well, so activating mTOR is something you'll definitely want to avoid. Toward this end, in addition to avoiding BCAA supplements, I recommend limiting your protein intake to about 40 to 70 grams per day, depending on your lean body mass.
Taking leucine as a free form amino acid supplement should also be avoided, as intravenous administration of free form leucine has shown to cause severe hyperglycemic reactions and insulin resistance. Hence, to get the benefits without the side effects, make sure you get your leucine from food only.
What Are the Best Food Sources of BCAAs?
BCAAs are found in a number of healthy protein-rich foods, including organic grass-fed beef, wild Alaskan salmon, pastured egg yolks, raw grass-fed cheese, quinoa, pumpkin seeds and nuts. One of the best sources, however, is whey protein concentrate, which has one of the highest concentrations of leucine.
The typical requirement for leucine is 1 to 3 grams daily. However, to optimize its anabolic pathway for muscle growth and repair, you need as much as 8 to 16 grams of leucine daily. One 3-ounce serving of whey protein has 8 grams of leucine (compared to just 1.6 grams in salmon or 1.4 grams in egg yolk).
This likely explains why whey protein concentrate has been found to stimulate muscle protein synthesis and has been called the ideal fitness food when consumed just before or after a workout.
In fact, another study published in the journal Medicine and Science in Sports & Exercise (MSSE) showed the amino acids found in high-quality whey protein also activate certain cellular mechanisms, including a mechanism called mTORC-1, which in turn promote muscle protein synthesis, boost thyroid and also protect against declining testosterone levels after exercise.22
To ensure you're getting a high-quality product, be sure your whey protein concentrate supplement comes from organically raised, grass-fed raw cows' milk (to ensure the whey is free of GMOs, pesticides and hormones) and is cold processed, as heat destroys whey's fragile molecular structure.
What Are the Serious Downsides of Using Too Many BCAAs?
Now that I reviewed many of the benefits of BCAAs you need to be aware that they are in no way shape or form a magic bullet and if you are going to use them they need to be carefully used. This is not a supplement or food that you want to take high doses of on a regular basis. Why?
The primary reason is that they are very potent stimulators of one of the most important metabolic signaling pathways in your body, mTOR. Excess protein, but BCAAs, and leucine in particular, will activate mTOR in a profoundly negative way. This can be fine if you are seeking to build muscle tissue but a very bad idea to use every day or times when you are not seeking to build muscle.
Elevated mTOR levels are similar to elevated insulin levels and involve many of the same metabolic players like IFG-1, AMPK and PGC 1 alpha. Just like insulin you need some or you will develop metabolic complications, in insulin's case type 1 diabetes. But if you have too much insulin for long periods of time you develop type 2 diabetes.
Similarly elevated mTOR signaling will contribute to increased risk of cancer because it suppresses autophagy and mitophagy, or the breakdown and recycling of defective calls and mitochondria. This metabolic perversion will also increase your risk of heart and diseases.
mTOR activation also suppresses mitochondrial biogenesis or the ability of your body to reproduce new mitochondria which are the powerhouse of your cells. I discuss this all in great detail in my new book, "Fat for Fuel," which comes out in May 2017. So like most things in life you need to keep it balanced. I believe BCAAs can be very dangerous to your health, but only when used in excess.
They can be highly beneficial if used in targeted specific ways when you strength train to build muscle mass that is so important as you age. I personally believe grass-fed whey protein concentrate, not isolate, is the best balanced whole food source of BCAAs and the one I use a few times a month, as I am convinced it is far superior to isolated BCAA supplements.