What is it? Leucine is the main branch chained amino acid (BCAA) responsible for muscle protein synthesis and muscle retention.
Who Should take it? Trainers wanting to improve their body composition, those trying to build/retain muscle, and especially any persons suffering from a muscle-wasting disease, including the elderly.
What does it do? Leucine is an activator of the protein known as mTOR (mammalian Target of Rapamycin), which then induces muscle protein synthesis via S6K (protein kinase involved in signal transduction). Leucine seems to induce mTOR activity via increasing intracellular calcium. The studies assessing leucine mostly look at muscle protein synthesis when additional leucine is added to the diet or to a test meal, and it appears that leucine is able to reliably increase muscle protein synthesis after test meals. Leucine appears to be most effective at promoting gains in muscle in people with lower dietary protein intake and in the elderly (who tend to have impaired muscle protein synthesis in response to the diet).
Leucine also helps with muscle retention as it preserves lean mass from breakdown, making it the perfect supplement for intra-workouts, hence the popularity of higher ratio BCAAs (higher Leucine content).
How do I take it? Add 2.5g - 5g to your pre-workout for enhanced recovery, protein synthesis and to prevent muscle catabolism during training. Consume up to 5g with other meals to increase post-prandial protein synthesis, especially if the meal is low(er) in protein.