L-Isoleucine is an amino acid, one of three known as branched chain amino acids (BCAAs). The others are L-Leucine and L-Valine. L-Isoleucine is an isomer of Leucine. It is important in the regulation of blood sugar, and also helps increase energy level. L-Isoleucine can be obtained through the foods you eat or supplements. Some of these foods include meat, fish, eggs, beans, nuts and seeds.