Laboratory rats and mice are usually confined to cages that markedly restrict their physical activity, and are provided with food ad libitum . However, animals fed arestricted amount of food, corresponding to about 50-60% of the average food consumption of rats fed ad libitum show a reduced size and develop age-related diseases such as tumors and kidney diseases, as well as a depressed age-related decline of protein and energy metabolism and physiological functions, resulting in prolonged longevity. In this review, the beneficial effects of food restriction we discussed from the viewpoint of age at the start of diet restriction, the kinds of nutrients that should be restricted, and the level of restriction, based on findings in animal studies. The author proposes energy requirements for frail elderly persons living in nursing homes.