Applied nutrition leucine 4k is a pure essential amino acid powder that contains the main amino acid leucine leucine is known as the primary essential amino acidr leucine is an essential amino acid due to the fact that our bodies requires this but does not make it so it must be supplementedr applied nutrition leucine 4k is made for anyone seeking muscle repair and improved recovery times perfect to be taken before or after a workoutr leucine is an essential branch chain amino acid it