Leucine

What it is studied for

The strongest rated effects first. Bars show the size of the effect, the letter grades the evidence, and each rating lists the studies behind it.

Muscle RecoveryFitnessModerateA 3 studies

Strength TrainingFitnessSmallBNo linked study

Physical EnergyEnergySmallCNo linked study

Energy CrashesEnergySmallCNo linked study

Endurance and staminaFitnessSmallCNo linked study

Every rating with its studiesGrouped by health goal, with the publications behind each rating

Why is leucine linked to muscle?

Leucine is an essential branched-chain amino acid. It participates in signaling that stimulates muscle protein synthesis, prompting research on age-related muscle loss. A short-term biological response does not establish lasting gains in strength. 1

Key studies

The most recent publications linked to Leucine's ratings.

Leucine-Enriched Essential Amino Acids Improve Recovery from Post-Exercise Muscle Damage Independent of Increases in Integrated Myofibrillar Protein Synthesis in Young Men2020 Effect of a leucine-enriched essential amino acids mixture on muscle recovery2019 Protein-leucine ingestion activates a regenerative inflammo-myogenic transcriptome in skeletal muscle following intense endurance exercise.2016

Why people take it

Fitness21.1%

Energy20.7%

Essential Health20.5%

Immune Support9.7%

Weight Management6.5%

Cognition5.2%

SuppCo community snapshot, 2026-09-28. Reasons for use are not evidence that it works.

Questions people ask

Is a muscle-building signal enough to prove benefit?

No. Muscle protein synthesis and long-term strength are different outcomes, and isolated leucine did not improve the main muscle measures in the review. 1

Is leucine only found in animal foods?

No. Legumes and nuts also provide it. 2

Is 4 g a recommended daily supplement dose?

No. BfR’s value is safety guidance for supplemental isolated leucine, not a recommendation to consume that amount. 3