← All supplements

Leucine

Supplement branched-chain amino acid fitness
Aka: L-leucine
Brands seen in Singapore: California Gold Nutrition, MuscleTech, Nutricost, Swanson Vitamins, Super Nutrition
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
Signals muscle protein synthesis · not a solo supplement
When to take
Spread across meals · 1–3 g per meal in ISSN's stand
Take with
A complete protein — leucine alone lacks the other EAAs
Pros & cons
Pros
  • ISSN: 1–3 g per meal appears to trigger translation
  • ODS: leucine might stimulate synthesis in worked muscle
  • Safe limit near 500 mg/kg a day in study populations
Cons
  • ODS: single amino acids have not consistently helped
  • ISSN: leucine on its own is not the way to supplement
  • Whey carries more leucine than casein or soy already
Sources
  1. NIH ODS — Exercise and Athletic Performance (HP), BCAA section · read 2026-08-27
    what it says
    “The BCAAs, especially leucine, might also stimulate protein synthesis in exercised muscle”
  2. NIH ODS — Exercise and Athletic Performance (HP), BCAA implications for use · read 2026-08-27
    what it says
    “Studies have not consistently shown that taking supplements of BCAAs or any of their three constituent amino acids singly enhances exercise and athletic performance, builds muscle mass, or aids in recovery from exercise”
  3. NIH ODS — Exercise and Athletic Performance (HP), BCAA safety · read 2026-08-27
    what it says
    “For leucine alone, studies suggest an upper safe limit of intake of 500 mg/kg per day in healthy young and elderly men, or about 38 g/day for a man weighing 75 kg”
  4. NIH ODS — Exercise and Athletic Performance (HP), protein powders and BCAAs · read 2026-08-27
    what it says
    “protein powders made from complete proteins, especially whey, which has more leucine than either casein or soy”
  5. ISSN position stand: protein and exercise (Jäger et al., JISSN 2017) — position statement 5 · read 2026-08-27
    what it says
    “Acute protein doses should strive to contain 700–3000 mg of leucine and/or a higher relative leucine content, in addition to a balanced array of the essential amino acids (EAAs)”
  6. Jäger et al., JISSN 2017 — amino acid summary · read 2026-08-27
    what it says
    “In addition, doses of approximately one to three g of leucine per meal appear to be needed to stimulate protein translation machinery”
  7. Jäger et al., JISSN 2017 — leucine section · read 2026-08-27
    what it says
    “Even though leucine has been demonstrated to independently stimulate protein synthesis, it is important to recognize that supplementation should not be with just leucine alone”
  8. Jäger et al., JISSN 2017 — leucine and total EAA dose · read 2026-08-27
    what it says
    “increasing leucine concentration may stimulate increases in muscle protein, but a higher total dose of all EAAs (as free form amino acids or intact protein sources) seems to be most suited for sustaining the increased rates of MPS”
  9. HSA — Guidelines on Prohibited and Restricted Ingredients in Health Supplements and Traditional Medicines, GL-CHPB-1-012 Rev 001 (Oct 2025), Annexes A/B · read 2026-08-27
    what it says
    “The objective of this guideline is to highlight the substances of concern when used in HS and TM and is not meant to be an exhaustive list”
  10. iHerb Singapore — Leucine category page, default sort · read 2026-08-27
    what it says
    “Leucine: BCAA Powder for Muscle Growth & Recovery | iHerb … 1 - 24 of 24 results”
Report a correction View as JSON

Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.