What are BCAAs?  There are three branch chain amino acids (BCAAs), these are: isoleucine, leucine, and valine. 

BCAA’s (branch chain amino acids) are considered essential, as unlike other amino acids they cannot be manufactured in the human body, and they can only be obtained in our diet.  In total there are nine essential amino acids, but, BCAAs account for 35% of all the essential amino acids found within muscle protein.  They are needed for protein building and can be metabolised and used as an energy source during aerobic exercise.  BCAAs are present in all protein rich foods, but are found in the greatest amounts in red meat and dairy products.  Whey protein contains particularly high levels of BCAAs.

Isoleucine
Isoleucine, together with the other two branched-chain-amino-acids promote muscle recovery after physical exercise and on its own it is needed for the formation of hemoglobin as well as assisting with regulation of blood sugar levels as well as energy levels. It is also involved in blood-clot formation.
Deficiency of isoleucine

Deficiency of isoleucine is only found in people deficient in dietary protein but symptoms may include headaches, dizziness, fatigue, depression, confusion as well as irritability. Symptoms of deficiency may mimic the symptoms of hypoglycemia. This nutrient has also been found to be deficient in people with mental and physical disorders

Leucine
L-Leucine (C6H13NO2) is an essential branched-chain amino acid (BCAA) that's broken down in fat structures.

L-Leucine can not be made by the body, and must be acquired through food or dietary supplements.

It can be found in nuts, brown rice and whole wheat bread products.

What does it do and what scientific studies give evidence to support this?
     
L-Leucine comprises about eight percent of the total amino acid count in your body's protein structures; it is the forth most concentrated amino acid in skeletal muscle tissue.

As one of the three BCAA's, L-Leucine is essential to your basic health. It has athletic applications.

L-Leucine has many beneficial effects on sports performance. It helps preserve lean muscle tissue, it supplies the body with energy when under stress (i.e. when engaging in athletic activity), it preserves muscle glycogen (glucose stored in muscle tissue used to power muscular contraction), it maintains nitrogen balance, and it enhances thinking abilities that can decline as physical activity becomes more intense.

The effects of L-Leucine in the diet are profound. As the strongest of the BCAA's, L-Leucine is what's known as a "limiting nutrient" - meaning that you must have enough L-Leucine in proportion to other amino acids in order for your body to make use of what you eat. Simply: If you suffer from an L-Leucine deficiency, your body will not be able to make use of the protein that you give it - no matter how much protein you consume. And, unless you have enough L-Luecine, the money you spend on quality food and dietary supplements will be wasted.

To make the most of what you eat, you need two parts L-Leucine and two parts L-Valine for every one part of L-Isoleucine. You'll fail to get optimal results if you fall short of meeting this exact ratio.

Valine
Valine is a branched-chain amino acid (BCAA) that works with the other two BCAAs, isoleucine and leucine, to promote normal growth, repair tissues, regulate blood sugar, and provide the body with energy. Valine helps stimulate the central nervous system, and is needed for proper mental functioning.

Valine helps prevent the breakdown of muscle by supplying the muscles with extra glucose for energy production during intense physical activity. Valine also helps remove potentially toxic excess nitrogen from the liver, and is able to transport nitrogen to other tissues in the body as needed. Valine may help treat liver and gallbladder disease, as well as damage to these organs caused by alcoholism and drug abuse. Valine may help treat or even reverse hepatic encephalopathy, or alcohol-related brain damage.

Valine is an essential amino acid, which means that it cannot be manufactured in the body and must be obtained through dietary sources. Natural sources of valine include meats, dairy products, mushrooms, peanuts, and soy protein. Although most people get enough valine from their diet, there have been recorded cases of valine deficiency. Maple syrup urine disease (MSUD) is caused by the inability to metabolize leucine, isoleucine, and valine. The disease is so named because urine from affected people smells like maple syrup. A deficiency of valine may also affect the myelin covering of the nerves, and cause degenerative neurological conditions.

People that exercise a lot, have a low-protein diet, or are seriously trying to build muscle mass should consider valine supplementation. Valine is available in stand-alone supplemental form, but should always be taken together with the other two branched-chain amino acids, isoleucine and leucine. The ideal balance is 2 milligrams of leucine and valine for each 1 milligram of isoleucine. Combination supplements that provide all three of the BCAAs may be more convenient.

An excessively high intake of valine may cause a skin crawling sensation and even hallucinations. Too much valine in the diet can also disrupt liver and kidney function and increase the amount of ammonia in the body. People with impaired liver or kidney function should not take isoleucine without first consulting a physician, as large doses of amino acids may aggravate these condition