LEUCINE IS KING
Leucine acts much like a key to the ignition of a car. The car, in this case, is a muscle cell or fiber. The ignition turns on the process of muscle protein synthesis (MPS), which builds up the muscle protein that leads to more muscle growth. In more "science-y" terms, leucine activates a complex called mTOR, which ramps up muscle protein synthesis and therefore muscle growth.
FIRE UP YOUR FAT LOSS
If you are interested in maximizing fat loss, there's yet another reason why a 2:1:1 ratio is best. This is where the BCAA isoleucine comes in. Isoleucine appears to play a major role in providing BCAAs their fat-burning benefits.
Japanese researchers discovered that mice given isoleucine while eating a high-fat diet gained significantly less fat than mice not getting supplemental isoleucine. This was due to isoleucine's ability to activate special receptors, known as PPAR, that increase fat-burning and inhibit fat storage. PPAR works to increase the activity of genes that encourage greater fat-burning in the body while decreasing activity of genes that normally increase fat storage. This leads to a greater ability to burn fat with less chance of storing it.
It turns out that using a BCAA supplement that has a ratio much higher than 2:1:1 can work against you for energy, fat loss, and even muscle growth. Some high-ratio BCAA products provide only 500 mg or less of valine and isoleucine. Steer clear of these. That amount is not enough to keep you energized and blunt fatigue during your workouts. It may not be enough to maximize muscle protein synthesis and the resulting muscle growth.