> Lifespan and metabolic health are influenced by dietary nutrients. Recent studies show that a reduced protein intake or low-protein/high-carbohydrate diet plays a critical role in longevity/metabolic health. Additionally, specific amino acids (AAs), including methionine or branched-chain AAs (BCAAs), are associated with the regulation of lifespan/ageing and metabolism through multiple mechanisms. Therefore, methionine or BCAAs restriction may lead to the benefits on longevity/metabolic health. Moreover, epidemiological studies show that a high intake of animal protein, particularly red meat, which contains high levels of methionine and BCAAs, may be related to the promotion of age-related diseases.