Leucine metabolites and muscle growth during resistance training in men
What it found
Taking leucine metabolite supplements did not improve muscle thickness or strength beyond training alone in men.
All groups gained similar muscle size and performance over eight weeks.
What they found
Studies in people
Muscle thickness gains
All groups built thicker muscles over the eight weeks of training. The supplements did not lead to more muscle growth than the placebo.
Strength and power
Bench press and squat strength improved across all groups. Jump height and short burst power also rose, but the supplements offered no extra benefit over the placebo.
Blood markers
Levels of several hormones and a muscle damage marker changed over time in everyone. These shifts were about the same whether men took a supplement or a placebo.
What the authors conclude
- They found that none of the tested leucine metabolites gave any extra performance or muscle-building benefits.
- The authors advise that taking these specific supplements does not improve muscle growth or strength development in young adult men who lift weights.
How it was done
Some supplement makers suggest that breakdown products of leucine can boost the body changes people get from weight training. The authors wanted to test whether off-the-shelf versions of these compounds actually help build muscle and strength.
Forty men were split into four groups taking either one of three leucine metabolite supplements or a placebo. Everyone followed a full-body weight training routine three times a week for eight weeks. Researchers measured muscle thickness, strength, power, and blood markers at the start, at four weeks, and at eight weeks.
What it can’t tell you
- We summarised it from the abstract only.
- This trial only included men, so it cannot show whether women would see the same results.
- The study lasted eight weeks, so longer-term effects remain unknown.
Who paid
- Authors work at
- Laboratory of Physiology and Biochemistry of Exercise, PORTUGAL; Laboratory of Exercise and Health, PORTUGAL; Center for the Study of Human Performance, PORTUGAL
The paper
- Title
- Leucine Metabolites Do Not Enhance Training-induced Performance or Muscle Thickness
- Type
- Randomised controlled trial
- Evidence
- Studies in people
- Summarised from
- Abstract only
- Cite
- Teixeira FJ, Matias CN, Monteiro CP, et al (2019). Leucine Metabolites Do Not Enhance Training-induced Performance or Muscle Thickness. Medicine and science in sports and exercise. doi:10.1249/MSS.0000000000001754PubMed 30102677DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error