Life expectancy in Japan is high, suggesting that the Japanese diet has significant health benefits. However, these benefits have been called into question in the past 50 years, during which the Japanese diet has become increasingly westernized. Our studies focused on senescence delay and examined the effects of Japanese diets from different years in order to identify which Japanese diet is most effective in enhancing life expectancy and delaying senescence. Weekly menus from the years 2005, 1990, 1975, and 1960 were reproduced based on the National Health and Nutrition Survey in Japan and prepared as powdered foods. The senescence-accelerated mouse prone 8 (SAMP8) mice were fed standard laboratory chow supplemented with a 30% mix of Japanese meals from various years ad libitum throughout their lifetime. In addition, the control group was given standard laboratory chow only, in order to examine the development of mice reared under standard conditions. In the group that ingested the Japanese diet from 1975, life span was prolonged, senescence was delayed, and learning and memory capacities were maintained when compared to the group given the Japanese diet from 2005. The life span of the group that ingested the Japanese diet from 1990 showed a tendency to extend compared with that from 2005. This suggests that the traditional Japanese diet is more effective in enhancing life expectancy and delaying senescence than todayʼs Japanese diet.