Isoleucine. Molecular model of the amino acid isoleucine. Its chemical formula is C6.H13.N.O2. Atoms are represented as spheres and are colour- coded: carbon (blue), hydrogen (gold), oxygen (red) and nitrogen (dark blue). Amino acids are the building blocks of proteins. Isoleucine is an essential amino acid. It cannot be synthesised by the body and so needs to be obtained from food. It is found in almonds, cashews, eggs, meat, poultry, fish, lentils, and liver. Isoleucine is important in the body's metabolic energy production and helps muscle recovery after strenuous use. It is also needed for the production of haemoglobin (the oxygen-carrying pigment in human blood), blood sugar regulation and the formation of blood clots.