potatoprotein.com
potatoprotein.com

An independent research resource on potato protein isolate.

Reference

Leucine

**Leucine** is one of three branched-chain amino acids (BCAAs) — alongside isoleucine and valine — and is the essential amino acid most directly responsible for triggering muscle protein synthesis (MPS).

How leucine triggers muscle protein synthesis

Leucine functions as a signaling molecule, not merely a building block. Beyond its incorporation into new muscle tissue, it activates the mTORC1 pathway, the intracellular switch that initiates translation of muscle protein. Among the amino acids, leucine is singled out as the primary trigger for MPS; isoleucine and valine, its fellow BCAAs, do not stimulate the response to the same degree.

The International Society of Sports Nutrition’s position stand on essential amino acid supplementation places particular emphasis on leucine’s role in raising muscle protein synthesis (ISSN, 2023, PMID:37800468).

The leucine threshold

The leucine threshold describes the minimum amount of leucine in a single meal needed to maximally stimulate MPS. A protein dose below the threshold produces a muted anabolic response; reaching it appears to matter more than total protein grams for the acute signal, which explains why leucine content — not just protein quantity — governs a protein’s effectiveness.

A 2024 controlled study illustrates the principle. A 20 g plant-based protein blend supplied 1.5 g of leucine — half the leucine of an equivalent whey dose — and produced a lower MPS response. When free leucine was added to bring the blend to 3.0 g, its MPS response (0.049%/h) became statistically indistinguishable from whey (0.046%/h), closing the anabolic gap (Journal of Nutrition, 2024).

Leucine in plant and animal proteins

Plant-based proteins generally contain less leucine than animal proteins, which can make a given dose less effective at stimulating MPS (Current Developments in Nutrition, 2024, PMID:38846451). This is the central argument for matching plant-protein servings by leucine content rather than by gram weight. Potato protein isolate is worth noting among plant sources: a 2020 study found it stimulated muscle protein synthesis at rest and with resistance exercise in young women (Nutrients, 2020, PMID:32349353). For background on the ingredient itself, see what potato protein is.