Leucine. Molecular model of the amino acid leucine. Its chemical formula is C6.H13.N.O2. Atoms are represented as balls and are colour- coded: carbon (blue), hydrogen (gold), oxygen (red) and nitrogen (dark blue). Amino acids are the building blocks of proteins. Leucine is an essential amino acid. It cannot be synthesised by the body and so needs to be obtained from food. It is most concentrated in legumes, beef, peanuts, pork, fish, poultry, almonds and dairy products. Leucine is important in the body's metabolic energy production and helps muscle recovery after strenuous use. It also plays a role in repairing muscle and bone tissue, increasing the production of growth hormones and regulating blood sugar.