All nine of the above amino acids are essential, but only leucine, isoleucine, and valine have the namesake branched-chain chemical structure.
No need to get too science-y here, but if you want to see what I’m talking about, I cover the chemical structure at around the 3:30 mark in the above video. Simply put, the three BCAAs are the only aminos with the “branched” V-shape structure at one end (as seen via a chemical diagram). None of the other six EAAs have those branches.
That chemical structure is significant, to say the least. An amino acid’s structure and shape determines in large part how it will be digested, absorbed, and used by the body. The important thing to know here is that the branched structure allows leucine, isoleucine, and valine to bypass the liver completely and go straight to the muscles.
This is a huge deal! All the other EAAs must pass through the liver after ingestion. Once in the liver, the body decides if it’s going to (a) send the aminos to the muscles or (b) convert those aminos to glucose for energy.
Either of these two scenarios can happen with the other six EAAs. But with the three BCAAs, only one thing can happen because they bypass the liver: leucine, isoleucine, and valine get a free pass to the muscles!
This doesn’t happen with any other amino acids, including the EAAs not named leucine, isoleucine, or valine; maybe they go to the muscles, maybe not. With BCAAs, it’s essentially guaranteed they’re going to the muscles. And once there, they can stimulate muscle protein synthesis (MPS).
The key player here is leucine. We now know that leucine ignites MPS better than any other amino acid. And we want leucine to get to the muscles and spike MPS as quickly as possible. It can do so by skipping the liver and going straight to its desired destination, the muscles.