Leucine

What it builds

Leucine does two jobs, and the second is why it gets its own chapter in every sports nutrition textbook. As a building block it is simply the most-demanded of the nine: its requirement is the highest on the list. As a signal, it directly activates mTOR, the cellular switch that initiates muscle protein synthesis.

That dual role has a practical consequence. Muscle does not respond to a slow trickle of amino acids across the day. It responds to a meal that crosses a leucine threshold, which starts a pulse of building that runs for a few hours and then settles back to baseline. Clear the threshold three or four times a day and you get three or four pulses. Eat the same total protein spread thinly across eight snacks and you may get none.

Where leucine actually comes from

Leucine rides along with protein density, so the daily total is rarely the problem. Per-meal dosing is.

Ranked by a realistic portion rather than per 100 g, because nobody eats 100 g of pumpkin seeds. Figures are digestibility-adjusted, so these are the amounts the app credits you with, not the amounts printed on the packet. Computed live from the 72 foods in the AminoLens recommender pool.

Signs you might be short

Slow recovery from training, and difficulty gaining or holding muscle despite a protein total that looks more than adequate on paper.

The usual cause is not low daily intake. It is distribution: a tiny breakfast, a light lunch, and one enormous dinner carrying most of the day's protein. Only one of those meals ever crosses the trigger.

Pairs well with

Nothing exotic. Leucine follows protein density, so the fix is structural rather than culinary: move protein out of dinner and into breakfast and lunch until every feeding clears the trigger on its own.