What are BCAAs (branched-chain amino acids)?

In one line

BCAAs are three essential amino acids, building blocks of protein, grouped under one name because their shape has a branch that splits off.

What are BCAAs (branched-chain amino acids)?
The four letters on supplement tubs and gym drinks
You often see the letters BCAA on the colorful drinks people sip at the gym and on protein powder labels. The full name, branched-chain amino acids, sounds even stranger. This post starts with what protein is and then explains, step by step, what BCAAs are and what they do in the body.
In one line
A group of three of the pieces that make up protein
BCAAs are three of the small pieces that make up protein, called amino acids, grouped under one name. The three are named leucine, isoleucine and valine. BCAA is made from the first letters of Branched-Chain Amino Acids.
Protein and amino acids
Protein is a bead necklace, amino acids are the beads
The protein that makes up muscle is a long chain of small units called amino acids, linked one after another. Think of a bead necklace: each bead is an amino acid. Protein is built from 20 kinds of amino acids. When you digest protein in food, it breaks back down into amino acids.
Essential amino acids
9 of the 20 have to come from food
Of the 20 amino acids, 9 cannot be made by the body, so they have to come from food; these are called essential amino acids. The body makes the rest on its own. All three BCAAs are essential amino acids, and they are already in protein foods such as meat, eggs and milk.
The name 'branched-chain'
It means a chain that splits like a branch
Every amino acid has the same main body with a different tail attached, and this tail is called the side chain. The Korean name uses words meaning 'split branch' and 'chain'. The 3 BCAAs got their name because the carbon line in their side chain splits like a tree branch.
Their path through the body
They mostly pass the liver and head to muscle
When most other amino acids are broken down, it happens in the liver. But the first step of breaking down BCAAs hardly happens in the liver and takes place mainly in muscle. So after drinking BCAAs, blood leucine quickly rises to 4 times the starting level, and much of it reaches muscle.
What leucine does
A building block and start signal for muscle protein 'synthesis'
Stringing amino acid beads into new protein is called synthesis. Leucine is used as a building block in muscle protein synthesis. At the same time, it turns on a signal in muscle cells that says 'start synthesis.'
BCAAs alone
Synthesis rose, but less than in whey studies
When people drank only BCAAs right after a strength workout, muscle protein synthesis rose more than with a fake drink with no BCAAs. But the researchers said the rise was smaller than in earlier studies where people had whey protein (a protein powder taken from milk) with a similar amount of BCAAs.
Muscle soreness
Less soreness 1 to 4 days after hard exercise
Exercise hard enough to damage muscle leaves muscles sore a day or two later. After this kind of exercise, people who took BCAAs had less soreness from one to four days later than those who took a fake pill. Right after exercise there was no difference.
Eating a lot of leucine
Above 35 g a day for a 70 kg person, ammonia went up
Ammonia is a waste product made as the body digests and uses protein. The liver turns it into a less harmful waste that leaves in urine, and if it builds up in the blood it harms the brain. In a study that raised the amount of leucine bit by bit, blood ammonia went up above 35 g a day for a 70 kg (154 lb) person.
A common myth
Do BCAAs alone build muscle?
Because leucine turns on the synthesis signal, many people say BCAAs alone build muscle. But muscle protein synthesis needs all 9 essential amino acids, and BCAAs have only 3 of them. Without the other 6, synthesis cannot rise much. The name for all 9 together is EAAs.
Summary
BCAAs are 3 of the 9 essential amino acids
BCAAs are the group of three essential amino acids with a split-branch shape: leucine, isoleucine and valine. Muscle protein synthesis needs all 9 essential amino acids, so BCAAs alone cannot raise synthesis much. Related terms: EAAs (essential amino acids), leucine, whey protein.