Designed to offer antioxidant support, NAC is a derivative of the amino acid L-cysteine. L-cysteine is one of the amino acids, along with L-glycine and L-glutamine, that is needed to make and replenish glutathione - the 'master' antioxidant. However L-cysteine is often considered to be the rate-limiting step in its production and so NAC can supply the body with bioavailable L-cysteine. L-cysteine is found in most high-protein foods such as chicken, turkey, yoghurt, cheese and eggs. Not consuming enough L-cysteine rich foods may affect your ability to make glutathione. Therefore people who eat restricted diets may struggle to get enough L-cysteine from their diet.