Reference
The nine your body cannot make
There are twenty amino acids in human protein. Your body can manufacture eleven of them from other material. The other nine have to arrive in food, every day, and a shortage of any single one caps how much protein you can build from all the rest.
Two of the nine lines below are pools rather than single molecules. Cysteine can be made from methionine and tyrosine from phenylalanine, so WHO counts each pair together, and AminoLens follows the same convention the requirement tables were written in.
All nine, ranked by how much you need
Adult figures from WHO/FAO/UNU 2007, in milligrams per kilogram of body weight per day, with the daily total for a 70 kg adult alongside. These are the same numbers the app scores your meals against.
| Amino acid | In one line | mg/kg/day | At 70 kg |
|---|---|---|---|
| Leucine | The trigger. The amino acid that tells your muscles to build. | 39 | 2.73 g |
| Lysine | The one plant-based eaters actually need to watch. | 30 | 2.10 g |
| Valine | The third BCAA. Endurance and repair. | 26 | 1.82 g |
| Phenylalanine + Tyrosine | The aromatic pair. Raw material for dopamine, adrenaline and thyroid hormone. | 25 | 1.75 g |
| Isoleucine | One third of the BCAA trio. Glucose uptake and muscle fuel. | 20 | 1.40 g |
| Methionine + Cysteine | The sulphur pair. The legume eater's blind spot. | 15 | 1.05 g |
| Threonine | The gut's favourite. Quietly essential for mucus and collagen. | 15 | 1.05 g |
| Histidine | The one they added late. Essential, but your body whispers rather than shouts about it. | 10 | 700 mg |
| Tryptophan | The scarcest one. Precursor to serotonin and melatonin. | 4 | 280 mg |
Start with the two that actually run short
Seven of the nine are rarely the constraint on any diet with enough total protein. In practice two lines do nearly all the limiting, and they catch opposite people: lysine on grain-centric plant-based diets, and the sulphur pair on legume-heavy ones. If you read two of these pages, read those.
If your interest is muscle rather than adequacy, the page you want is leucine, which is less about your daily total than about what happens at each individual meal. And if you would rather start from your own situation than from a molecule, the how-protein-works cluster covers the same science organised by person.
Find out which one is limiting you
One photo of a real meal, and the Sankey shows you where the protein goes.
Analyse a meal