Leucine is one of the three branched-chain amino acids. Not only does leucine have benefits in combination with isoleucine and valine but as a stand alone compound it helps stimulate muscle protein synthesis (1). It is widely considered the most important amino acid. It may decrease the likelihood of muscle breakdown during physical activity while increasing muscular endurance (2). 

When to take Leucine 

Studies show that leucine is most effective when taken before or during exercise (3). The same goes for leucine in combination with isoleucine and valine. It is best to use leucine during workouts to maximize the potential benefits. 

1.Holecek M. Branched-Chain Amino Acids in Health and Disease: Metabolism, Alterations in Blood Plasma, and as Supplements. Nutr. Metab. 2018;15:33 doi: 10.1186/s12986-018-0271-1.                                                                                                                               2.Qin L., Xun P., Bujnowski D., Daviglus M.L., Van Horn L., Stamler J., He K., Intermap Cooperative Research Group Higher 3.Branched-Chain Amino Acid Intake Is Associated with a Lower Prevalence of Being Overweight or Obese in Middle-Aged East Asian and Western Adults. J. Nutr. 2011;141:249–254. doi: 10.3945/jn.110.128520.