Leucine

Studies in people

• Benefit

  Muscle mass and strength²

  In people with muscle loss, leucine with whey protein and vitamin D increased muscle mass, and strength improved only alongside exercise.

• Benefit

  Muscle loss with age³

  In older adults, leucine-enriched whey protein plus resistance training increased lean muscle mass, strength and physical performance.

• Benefit

  Muscle health in older adults⁴

  In people, leucine seems to help older muscles build protein, but no long studies prove it works.

• Benefit

  Muscle strength in older adults⁵

  In older adults, a supplement with leucine and vitamin D improved muscle mass and leg function over 13 weeks.

• Benefit

  Muscle growth with training⁸

  In men doing strength training, leucine added to whey protein built muscle and strength just as well as HMB.

Study type not stated

• Open question

  Muscle strength and growth⁹

  Leucine is one of three branched-chain amino acids that may help muscle growth, but studies disagree.

• Benefit

  Muscle loss while dieting¹⁰

  Leucine may help people keep muscle while losing weight on a low-calorie diet.

How it’s made and used

• Muscle growth and strength⁶

  In men doing weights, leucine metabolite supplements like HMB and α-HICA gave no extra muscle growth or strength.

• Protein threshold cell signal⁷

  In people, leucine switches on a cell signal only when a meal has more than about 25g of protein.

The signal at the top counts the findings in people and in animal and lab studies. A concern in studies of people outranks animal and lab studies, and “No concerns” needs at least two findings in people. Findings whose study type is not stated are shown but not counted. This page is a reference, not medical advice. It describes what regulators and published research say. Talk to a doctor or dietitian about your own diet.