Essential amino acids
BCAA stands for branched-chain amino acid. Your body uses 20-22 amino acids (the exact number is up for debate) to construct protein. Within this group of amino acids, you have essential amino acids (EAAs) and non-essential amino acids.
The essential amino acids are a group of nine amino acids that the body cannot synthesize on its own and must obtain them through the diet. The nonessential amino acids are ones the body can self-generate from a combination of the essential amino acids, carbohydrates, and fats, hence their being dubbed “nonessential.”
BCAAs are a special “subcategory” of the essential amino acids that obtained their name “branched-chain” due to their unique branch-like structure.
The three branched-chain amino acids are:
The nine essential amino acids are:
- Leucine (BCAA)
- Isoleucine (BCAA)
- Valine (BCAA)
Why are EAAS Important?
OK, now that you’ve got a handle on the different kinds of amino acids, we can start getting to the more pressing and important points of this article, such as whether or not BCAA are “useless.”
First up, let’s discuss why essential amino acids are important.
Well, muscles are made of protein, and protein is made up of amino acids. Your body synthesizes new proteins (and subsequently muscle) from these amino acids. However, muscle protein synthesis only occurs if all nine of the essential amino acids are present in sufficient quantities. That means that if just one of the essential nine amino acids is missing, protein synthesis grinds to a halt, and so do your gains.
Now, in order to for protein synthesis to even begin, your body needs to flip the “on” switch to start the protein assembly factory. The great thing about the human body is that there are multiple ways to flip this “on switch.”
The most powerful of activator or “switch flipper” of protein synthesis is the branched-chain amino acid leucine, the “king” of amino acids.  Leucine activates the mechanistic target of rapamycin (mTOR) pathway, which is the “switch” that turns on muscle protein synthesis.
Other means for activating mTOR and ratcheting up protein synthesis include resistance exercise or consuming any type of mixed meal.  Consuming food, especially carbohydrates, whey protein, or individual amino acids such as leucine, triggers your body to release insulin, which in and of itself activates mTOR and gets your body’s protein-producing factory cranking full steam ahead. 
So, to recap, your body needs all nine of the essential amino acids present to build proteins, and the process of protein synthesis gets activated by one of several different triggers, leucine (one of the BCAA) being quite possibly the most potent potentiator of the protein production process.