Leucine

Leucine is an essential branched-chain amino acid (BCAA) and the primary activator of muscle protein synthesis through the mTORC1 pathway. It is the most anabolic amino acid known — acting as a molecular signal that 'tells' the muscle that protein is available and it is time to build. Naturally present in protein-rich foods such as meats, eggs and dairy, isolated supplementation is used to enhance the anabolic stimulus without adding extra calories.

• Primary activator of protein synthesis via mTOR
• Stimulates post-workout muscle recovery
• May be more efficient than full BCAA blend for protein synthesis
• Useful to maximize anabolism in low-protein meals
• Smaller and more precise dose than BCAA

• •Athletes seeking to optimize the anabolic stimulus per meal
• •People with borderline protein intake who want to maximize synthesis
• •Those who already use Whey and want to enhance the anabolic effect
• •Vegans and vegetarians with protein sources lower in leucine
• •Caloric restriction contexts to preserve muscle mass

2g to 5g per dose, preferably with meals or immediately post-workout. The leucine threshold to activate protein synthesis is approximately 2–3g per meal.

Isolated Leucine makes more sense than full BCAA when the goal is to maximize protein synthesis with a smaller dose and cost. If you already use Whey Protein (rich in leucine), the additional benefit is smaller. Isolated Leucine is especially useful to complement solid meals with lower leucine content — such as legumes, grains or plant proteins. If the goal is simply to preserve muscle while fasted, BCAA or isolated Leucine are equivalent.

Leucine is the amino acid with the strongest evidence for mTORC1 pathway activation, responsible for muscle protein synthesis. Studies show that there is a 'leucine threshold' per meal (around 2–3g) necessary to maximally activate protein synthesis. Meals with less leucine than this threshold have suboptimal anabolic response. Isolated leucine supplementation may be more efficient than full BCAA for this purpose, as it concentrates the active amino acid without diluting with Isoleucine and Valine.

Generally well tolerated. Very high doses may cause insulin resistance in the long term in some studies — keep dose within the recommended range. Amino acid imbalance at excessive doses.