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L-Leucine

L-Leucine

bcaa· Energy
A-Tier · Strong Evidence38 citations
Found in 84 products
Quick Answer:The clinical dose of L-Leucine is 2000–4000mg (2–4g) per meal or training dose, consistent with published MPS threshold research. L-Leucine is a branched-chain essential amino acid (BCAA) that serves as the primary nutritional activator of the mTORC1 (mechanistic target of rapamycin complex 1) signaling pathway.Found in 84 products on SuppVault.
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Products Containing L-Leucine
84 products contain L-Leucine.
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Mechanism of Action

Pharmacokinetics: Free-form L-Leucine is rapidly absorbed in the small intestine via LAT1 transporters. Plasma Tmax is approximately 30–60 minutes post-ingestion (free form), slightly delayed with food or whole protein sources. Bioavailability of free-form leucine is high (>90%). Half-life of plasma leucine elevation is approximately 2–3 hours. Peak MPS stimulation occurs 1–2 hours post-ingestion, returning toward baseline by 3–4 hours — supporting the concept of repeated leucine dosing across meals. Leucine is catabolized in skeletal muscle (unlike most amino acids which are hepatic) via branched-chain aminotransferase (BCAT) to alpha-ketoisocaproate (KIC), which is further converted to HMB (~5% of leucine oxidized) or acetyl-CoA. The leucine threshold for maximal MPS stimulation is estimated at 2–3g per meal in healthy young adults, with higher thresholds (~3–4g) potentially required in older adults due to anabolic resistance.

Works Best With
Isoleucine + Valine
Whey Protein
HMB (Beta-Hydroxy Beta-Methylbutyrate)
Carbohydrates
Questions About L-Leucine
What is L-Leucine? +
L-Leucine is an essential branched-chain amino acid (BCAA) that the body cannot synthesize — it must be obtained from food or supplements. It is found in high concentrations in animal proteins (meat, dairy, eggs) and is considered the primary amino acid responsible for triggering muscle protein synthesis (MPS).
How does L-Leucine work? +
L-Leucine activates the mTORC1 signaling pathway, the master regulator of muscle protein synthesis. When leucine levels rise in the blood after a meal or supplementation, it signals the body to build new muscle protein. This is why leucine content is considered a key quality metric for protein sources.
What is the best dose of L-Leucine? +
Research suggests a threshold of approximately 2–3g of leucine per meal is needed to maximally stimulate MPS in healthy young adults, with some evidence for 3–4g in older adults who have higher anabolic resistance. Most clinical protocols use 2–5g per dose. Doses below 2g may be insufficient to independently trigger MPS.
When is the best time to take L-Leucine? +
Post-workout is the most evidence-supported timing, as mTORC1 sensitivity is elevated after resistance training. Leucine can also be added to meals with low-leucine protein sources (e.g., plant proteins) to bring them closer to the MPS threshold. Pre-sleep leucine has emerging support for overnight muscle protein synthesis.
What are the side effects of L-Leucine? +
L-Leucine is generally well-tolerated at clinical doses (2–5g). The most common issue is its intensely bitter taste. Large single doses (>5g) taken on an empty stomach may cause transient nausea. Chronically very high intakes may contribute to excess nitrogen load, relevant for those with impaired kidney function.
Do I need to cycle L-Leucine? +
No cycling is required or recommended. L-Leucine is a natural amino acid consumed daily through food. Consistent supplementation does not appear to cause receptor downregulation or tolerance.
What is the best form of L-Leucine? +
Free-form L-Leucine powder has the fastest absorption and is used in the majority of clinical research. It is the most cost-effective option. The primary drawback is its strong bitter taste. Leucine within whole protein (e.g., whey) is equally effective for most users. Creatyl-L-Leucine is a distinct compound with insufficient evidence to recommend.
Who should take L-Leucine? +
L-Leucine supplementation is most beneficial for: (1) those consuming low-leucine protein sources (e.g., plant-based diets); (2) older adults with anabolic resistance who need higher leucine per meal to trigger MPS; (3) athletes in caloric deficit trying to preserve lean mass; (4) individuals unable to meet protein targets through diet alone.
Who should not take L-Leucine? +
Individuals with Maple Syrup Urine Disease (MSUD) must not take leucine or any BCAA — this is a serious metabolic contraindication. Those with isovaleric acidemia, severe kidney disease, or ALS should avoid supplementation or consult a physician. Individuals on insulin or blood sugar medications should monitor glucose levels due to leucine's insulinogenic properties.
Can I stack L-Leucine with other supplements? +
Yes. L-Leucine is commonly stacked with isoleucine and valine (completing the BCAA trio), whey or other protein supplements, HMB (a leucine metabolite with anti-catabolic properties), and carbohydrates to amplify the insulin-driven anabolic response post-workout.
Is L-Leucine safe for long-term use? +
Long-term use at supplemental doses (2–5g/day) appears safe in healthy individuals based on available evidence. It is a natural dietary amino acid consumed throughout life. Individuals with metabolic disorders (see contraindications) or impaired renal function should consult a healthcare provider.
Can I get L-Leucine from food? +
Yes. L-Leucine is found in all complete protein foods. Richest sources include: whey protein (~10–11% leucine), chicken breast (~8%), beef (~8%), eggs (~8.5%), and dairy. A 30g serving of whey protein provides approximately 3g of leucine, often sufficient to meet the MPS threshold.
Is there a difference between branded and generic L-Leucine? +
Standard L-Leucine is a commodity ingredient with no meaningful difference between suppliers for purity grades meeting USP/food-grade specifications. There is no patented form of plain L-Leucine with clinical differentiation. Creatyl-L-Leucine is a distinct compound, not a branded version of L-Leucine.
Does L-Leucine require a loading phase? +
No loading phase is needed. Unlike creatine, leucine does not accumulate in tissue stores. Each dose acts acutely on the mTORC1 pathway; benefits from consistent supplementation reflect repeated stimulation of MPS over time.
Does L-Leucine interact with any medications? +
Potential interactions include: insulin and oral hypoglycemics (leucine is insulinogenic, may enhance blood glucose-lowering effect); mTOR inhibitors like rapamycin/sirolimus (leucine directly activates mTORC1, potentially counteracting these drugs); and theoretically, medications metabolized via branched-chain amino acid pathways. Consult a physician if on these medications.
Deep Content
Everything About L-Leucine Article

What is L-Leucine?

L-Leucine is a branched-chain amino acid (BCAA). The provided sources were insufficient to generate a comprehensive guide. The primary source for scientific evidence (Examine.com) was unavailable, and other materials focused on market data and brand-specific news rather than the ingredient's clinical effects.

What The Data Shows

No clinical research was available in the provided documents. A survey of 65 commercial supplements containing L-Leucine found a wide dosage range, from 37.5mg to 5000mg per serving, with a median dose of 2500mg. This suggests that doses in the 2.5g to 5g range are common in the sports nutrition market. One article mentioned a specific form, Creatyl-L-Leucine, used in an energy drink, but did not provide data on its efficacy.

Dosing

Without clinical data from the sources, a definitive dosing guide cannot be established. However, based on market analysis, a typical dose appears to be around 2500mg (2.5g). Consumers should be aware that many products on the market contain this amount, while doses significantly lower may not align with common industry formulations.

The Bottom Line

Due to the lack of accessible scientific evidence in the provided sources, no conclusions can be drawn about L-Leucine's benefits, mechanisms, or safety. The only available information pertains to its presence in commercial products and common dosages found on the market.

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