Leucine is an "essential amino acid" meaning that since your body can't make it, it has to enter your body via the mouth.
It plays a key role in breaking down protein to repair muscles and other lean tissue in your body. If you're exercising regularly, you need to be taking in Leucine in order to make sure your body has what it needs to repair itself.
The best way to get it, with regard to workout recovery, is in powered form immediately after a workout (most products that say "BCAA" ("Branched Chain Amino Acid" on the side probably has it). If you don't want to do that you can always get it through the common staples of eggs, milk, and red meat, or through the less common dietary selections of Bearded Seal and Beluga whale! Whatever floats your boat.
Either way, Leucine is the key player for an anabolic effect in your body, and will keep you from losing muscle while maximazing fat loss due to muscle mass retention.
