Key facts
- Nine of the 20 amino acids are 'essential'.
- Must come from the diet — the body can't make them.
- Complete proteins contain all nine in good amounts.
- Include leucine, the key trigger for muscle growth.
Amino acids are the building blocks of protein. Your body can manufacture eleven of them, but the other nine — the essential amino acids — must come from what you eat. Without enough of all nine, your body can't fully build the proteins it needs, including muscle.
Foods that contain all nine EAAs in good proportions are called 'complete' proteins — mostly animal sources like meat, eggs, and dairy, plus soy. Plant proteins are often lower in one or two EAAs, but eating a variety across the day easily covers the full set. The EAAs, led by leucine, are what actually drive the muscle-building response to protein.
Frequently asked questions
What's the difference between essential and non-essential amino acids?
Essential amino acids must come from food because the body can't make them. Non-essential ones can be synthesized internally, so a dietary shortfall is less of a concern.
Can vegetarians get all essential amino acids?
Yes. Eating a variety of plant proteins (legumes, grains, soy, nuts) across the day provides all nine essential amino acids, even if individual sources are incomplete.
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