Essential amino acids
Nine amino acids that the human body cannot make and that must be supplied by food.
The 9 essential amino acids (EAAs) are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Of the 20 amino acids that make up proteins, the body makes the other 11 (non-essential amino acids).
Each EAA has a distinct role:
- Leucine, isoleucine, valine (BCAAs): branched-chain, essential for muscle synthesis (35% of the amino acids in muscle)
- Lysine: collagen synthesis, immunity
- Methionine: sulphur metabolism, epigenetics
- Tryptophan: precursor of serotonin (mood)
- Phenylalanine: precursor of noradrenaline (energy, attention)
- Threonine: gut integrity
- Histidine: immune regulation
A fresh angle: the Academy of Nutrition and Dietetics (2023) questioned the terms « complete/incomplete protein », judging them misleading for consumers. Why? Because you can get all the EAAs from plants if you eat enough calories and combine foods sensibly (e.g. pulses rich in lysine + cereals rich in methionine).
But there is a real concept: the limiting amino acid, the one present in insufficient quantity that caps the use of all the others. For example, a pulse on its own may see its efficiency capped at 45% if lysine is too low. It is a nuanced debate: for households with varied access to food, plant proteins are enough; in contexts of food poverty, ensuring EAAs is critical.