Citable fact
«Leucine» — evidence level B. Dosage: 2.5-5 g per day as a supplement; a single serving of 2.5-3 g. For comparison: 25 g of whey protein contains about 2.5-3 g of leucine. Source: PMID 32079916, permanent link to the source in the list below.
How it works
Leucine is a branched-chain amino acid that directly activates the mTORC1 signaling pathway and triggers muscle protein synthesis. It also serves as a signal of amino acid availability. However, protein synthesis depends not only on the signal: the full set of essential amino acids is needed as building material. Therefore, additional leucine on top of a complete protein does not increase the anabolic response - the signal is already saturated.
Dosage and intake
2.5-5 g per day as a supplement; a single serving of 2.5-3 g. For comparison: 25 g of whey protein contains about 2.5-3 g of leucine
With a meal containing a complete protein; alone - within 1-2 hours after strength training. Intake on an empty stomach without the other amino acids is ineffective
Forms
Free L-leucine, powder or capsules. Practically tasteless, poorly soluble in water. It is part of whey, egg and meat protein
What is confirmed
- Works as a signaling molecule for muscle protein synthesis
- May be useful with low total protein intake, in the elderly and with a plant-based diet with an incomplete amino acid profile
- Helps assess the quality of a protein product by its leucine content
Adverse effects and limitations
- With adequate protein (1.6 g/kg and above), the supplement gives no additional gain in muscle and strength
- Large single doses (10 g and more) often cause nausea and diarrhea
- Taking a single amino acid without the other essential amino acids does not support protein synthesis, but only signals it
- Does not replace complete protein in total amount
Interactions
- Synergistic with the full set of essential amino acids and with protein intake in general
- Competes for the same transporters with other large neutral amino acids (valine, isoleucine) when large doses are taken on an empty stomach
- With insulin, the anabolic response to leucine is enhanced, but this does not change the practical conclusions
Who must not use it
- Under 18 years: Safe as part of protein; separate supplements are not needed by children and adolescents with normal nutrition
- Pregnancy and lactation: There are no data on taking separate leucine supplements during pregnancy; leucine is required as part of a complete protein according to the usual norms
- Kidney failure - only as prescribed by a physician
- Inherited disorders of branched-chain amino acid metabolism (maple syrup urine disease) - contraindicated
- Liver failure - protein restriction according to clinical indications
Sources
- Leucine Supplementation Has No Further Effect on Training-induced Muscle Adaptations · DE Andrade IT, Gualano B, Hevia-Larraín V · Medicine and science in sports and exercise, 2020 · PMID 32079916
- International Society of Sports Nutrition Position Stand: protein and exercise · Jäger R, Kerksick CM, Campbell BI · Journal of the International Society of Sports Nutrition, 2017 · PMID 28642676
- A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults · Morton RW, Murphy KT, McKellar SR · British journal of sports medicine, 2018 · PMID 28698222
See also
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