Isoleucine is an essential amino acid and one of the three branched-chain amino acids (BCAAs). Your body cannot make it, so you must get it from food or supplements. It helps build muscle protein and supports energy production during exercise.
People take isoleucine before or after training to aid recovery, ease muscle soreness, and maintain energy output. You can use it solo or inside a BCAA blend.
Take it on an empty stomach or with meals based on what fits your schedule. Most people handle it fine, but anyone with a relevant metabolic condition should check with a doctor first.