The mechanisms by which dietary restriction of the amino acid methionine exerts beneficial effects on oxidative damage towards rat liver mitochondria are discussed. It is suggested that methionine restriction decreases amino acid utilization in protein synthesis which, by decreasing synthesis of non-essential amino acids from carbohydrate precursors, also decreases formation of the highly deleterious glycolytic by-product methylglyoxal, a well-recognised source of age-related damage including formation of reactive oxygen species, mitochondrial dysfunction and proteotoxicity. Additionally, decreased protein synthesis will lower the error-protein load which the protein quality system (proteasomal and autophagic) must deal with to maintain proteostasis.