What Is L-Leucine and Why Does Dosage Matter?
L-leucine is a branched-chain amino acid (BCAA) and the primary driver of muscle protein synthesis (MPS) among the three BCAAs. Unlike isoleucine and valine, leucine directly activates the mTORC1 pathway — the central anabolic signalling cascade in muscle tissue. Getting the l-leucine dosage right is therefore central to maximising the anabolic response to resistance training and protein feeding.
Studied Effective Dose Ranges
Research consistently shows that a leucine dose of approximately 2–3 g per meal is needed to maximally stimulate MPS in young adults (Norton & Layman, 2006). This threshold concept — often called the "leucine trigger" — means that meals or shakes falling short of this amount may produce a sub-maximal anabolic response even if total protein is adequate.
In older adults, the leucine threshold appears to be higher, with some studies suggesting that doses closer to 3–4 g per meal are beneficial to overcome age-related anabolic resistance (Wall et al., 2013).
BCAA supplements at maxfit.ee that provide meaningful leucine per serving include OstroVit BCAA 5000mg 150caps and DY HIT BCAA 10:1:1 400g Apelsin — the 10:1:1 ratio means leucine dominates heavily. For lysine supplementation alongside leucine, NOW L-Lysine 1000mg 100tabs is available.
Dose by Goal and Bodyweight
| Goal | Leucine per Meal | Notes |
|---|---|---|
| Muscle maintenance | ~2 g | Achievable from ~25 g quality protein |
| Muscle growth (young adults) | 2–3 g | Supplement if protein source is low in leucine |
| Muscle growth (older adults) | 3–4 g | Higher threshold due to anabolic resistance |
| Post-workout bolus | 2–3 g isolated leucine | May enhance MPS when protein intake is borderline |
Upper Limits
EFSA has not established a formal UL for leucine. Research in humans suggests that intakes up to around 500 mg per kg body weight per day are generally tolerated without adverse effects, though most practical supplementation stays well below this. Chronically very high leucine intakes may theoretically interfere with uptake of other BCAAs (isoleucine, valine) by competing for shared transporters, which is why most BCAA products include all three amino acids.
Timing Relative to Dose
The post-workout window remains meaningful for leucine specifically. A meta-analysis found that protein-leucine timing around resistance exercise was associated with greater lean mass gains compared to timing-agnostic approaches (Cermak et al., 2012). Practically, taking leucine-containing protein or a BCAA supplement within two hours of training maximises the convergence of elevated mTORC1 sensitivity and amino acid availability.
For those eating high-protein meals throughout the day, distributing leucine across three to four meals may offer an advantage over concentrating it in one or two larger doses.
Practical Protocol
- Check your protein sources first. Whey, eggs, and beef are naturally high in leucine (~8–11% of protein by weight). If your main sources are plant-based, supplemental leucine is more warranted.
- Target 2–3 g leucine per meal. This is achievable from roughly 25–30 g of whey protein per serving.
- Consider a post-workout bolus. If your post-training meal is delayed or low in protein, a BCAA product with a high leucine ratio bridges the gap.
- Do not over-rely on isolated leucine. Complete protein sources or full EAA profiles are generally superior to leucine alone for sustained MPS.
- Pair with adequate total protein. Leucine thresholds assume total protein intake is otherwise sufficient. Leucine supplementation does not compensate for chronically low protein intake.
FAQ
How much l-leucine should I take per day?
For most active adults targeting muscle growth, ensuring 2–3 g of leucine per main meal — particularly around training — is the evidence-based target. Isolated leucine supplements of 2–3 g per dose are commonly used. Total daily intake from all protein sources will typically far exceed this.
Should I take leucine before or after training?
Either works. Research supports leucine-containing protein or BCAAs taken within roughly two hours of resistance training. Pre-workout leucine may also reduce muscle protein breakdown during exercise. The most important factor is consistency rather than the exact timing window.
Is leucine the same as BCAA?
No. BCAAs consist of three amino acids: leucine, isoleucine, and valine. Leucine is the one with the strongest MPS-signalling effect. BCAA products deliver all three; some use a higher leucine ratio (e.g., 10:1:1) to amplify the leucine effect.
References
Norton, L. E., & Layman, D. K. (2006). Leucine regulates translation initiation of protein synthesis in skeletal muscle after exercise. Journal of Nutrition, 136(2), 533S–537S. https://pubmed.ncbi.nlm.nih.gov/16424142/
Wall, B. T., Hamer, H. M., de Lange, A., Kiskini, A., Groen, B. B., Senden, J. M., Verdijk, L. B., & van Loon, L. J. (2013). Leucine co-ingestion improves post-prandial muscle protein accretion in elderly men. Clinical Nutrition, 32(3), 412–419. https://pubmed.ncbi.nlm.nih.gov/23043721/
Cermak, N. M., Res, P. T., de Groot, L. C., Saris, W. H., & van Loon, L. J. (2012). Protein supplementation augments the adaptive response of skeletal muscle to resistance-type exercise training: a meta-analysis. American Journal of Clinical Nutrition, 96(6), 1454–1464. https://pubmed.ncbi.nlm.nih.gov/23134885/
