Amino Acids Supplements - Amino Acid Safety and Amino Acid Toxicity


Amino Acids are the building blocks of protein. They can be broken down into different categories. The non-essential amino acids, the essential amino acids, and then the branched chain amino acids (which are three of the essential amino acids).

The branched chain amino acids (BCAAs for short) are the most abundant of the essential amino acids.

Quite Simply, the essential amino acids are the amino acids regarded as essential for human life. They are leucine, isoleucine, valine, phenylalanine, threonine, tryptophan, methionine, lysine and histidine. These amino acids are considered essential since we cannot ’make’ them in our bodies so we must consume them in our diets on a semi-regular basis.

Of this list, Leucine, IsoLeucine and Valine (collectively the Branched Chain Amino Acids) make up 35% of the essential amino acids found in human muscle.

The BCAAs are well known for their important role in muscle growth by signaling protein synthesis through the mTOR pathway, and their ability to stimulate insulin. During the digestion process the proteins we consume are broken down into individual amino acids and these amino acids then enter circulation. They can either be used to build new proteins or be burned as fuel to produce energy. This is one of the main reasons why people follow high protein diets and take amino acid supplements. It is also why people take protein after workouts.

Dietary sources of the branched chain amino acids include most high protein foods, such as Dairy and red meat as well as whey protein and eggs.

As an example, three ounces of lean ground beef contain 2 grams of leucine and 4 grams of total branched chain amino acids.

The simple science of BCAAs and their role in protein signaling has lead to the rise of their popularity as a muscle building supplement. This is the reason why Amino Acid Supplements like BCAA pills and powders continue to be popular items as sports-supplements and maintain their popularity among bodybuilders.

BCAAs play an essential role in whole-body metabolism acting as a transport system to move nitrogen through the body for synthesis of amino acids They also act as hormone-like signals of nutrient status.

While all amino acids have levels that could be considered toxic, it's important to examine the toxicity of the BCAAs specifically since they are the most supplemented of the amino acids.

There are several ways that the body can prevent BCAA toxicity (including transforming BCAAs into body fat and oxidizing BCAAs as a fuel source).

Most of the safety data on BCAAs is based on animal models and show a relatively high tolerance to elevated BCAA intakes. However, when extrapolating from animal studies to humans, we must consider that humans may be more susceptible to toxicity than rats due to lower activity of the major catabolic enzymes. In other words, we may not be able to handle the same overload of BCAAs as the research rats can.

One thing to always consider when taking any supplement is the passage of that substance across the blood brain barrier. Things like caffeine and alcohol easily cross this barrier and the effect they can have on you is obvious, and more specifically when you’re at a toxic level it becomes VERY obvious (this is essentially what happens when someone is intoxicated on alcohol). This same passage across the blood brain barrier happens with the branch chain amino acids.

There are specific transporters at the blood brain barrier for BCAAs and as such elevations in blood levels of BCAAs can cause elevations in the level of branched chain amino acids found in the brain. Because of this fact the BCAAs seem to act as donors for glutamate synthesis in the brain.

There have been safe upper limits proposed for the BCAAs, which has been suggested at 15 mg of BCAAs per kg per day per Branched Chain Amino Acid, which roughly corresponds to 3 grams of BCAAs per day. This is lower than the amount found in 3 ounces of lean ground beef.

However, some scientists have suggested that this suggestion vastly overestimates the potential BCAA toxicity in the human population, as humans have consumed ’up to 20-fold higher daily doses in addition to their daily protein loads with no ill effect’

In fact, based on studies with young experimental animals a rather large dietary excess well above requirement of an individual BCAA is well tolerated when consumed in diets containing sufficient amounts of protein and the other 2 BCAAs.

This is probably because adipose tissue can also act as a major site of both BCAA oxidation and storage (as body fat). This enables the body to tightly regulate the BCAA content in the blood and prevent toxic excess.

Leucine specifically is a strong activator for synthesis of hepatocyte growth factor in the liver, helping with liver regeneration. And side effects and associated toxicities are rare.

Your body will work to regulate and control the amount of BCAAs that cross the blood brain barrier to avoid a negative and toxic level. It seems that one of the ways it does this is by storing it as bodyfat when the upper limit of tolerable BCAA content has been reached.

The bottom line is that I see very little evidence that a high protein diet could lead to amino acid toxicity, and even supplementing with amino acid supplements seems to have a very low risk assocaited with it.

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Branched-Chain Amino Acids and Brain Function. Fernstrom J. J Nutrition. 2005

Branched chain amino acid supplementation in patients with liver disease. Marchesini G. J Nutr. 2005.

Brain Amino Acid Requirements and Toxicity: The example of Leucine. J Nutr 2005

Tolearance for Branched Chain Amino Acids in Experimental Animals and Humans. Baker DH. J Nutr 2005

Observations of Branched Chain Amino Acid Administration in Humans. Matthews DE, J Nutr 2005

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