Length of life and caloric intake

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Abstract
Longevity studies were undertaken to assess the influence upon length of life of both the level of food intake and the age of the rat when an experimental dietary regimen was instituted. A purified diet containing 22% casein was offered to the rat from the 21st day of life in ad libitum or in restricted amounts. These regimens were either maintained throughout life or changed at 70, 300, or 365 days of age. When a change in food allotment was made, the new regimen was then maintained for the remainder of the animal’s lifetime. Length of life was found to be influenced by the dietary experiences early in life. A period of restriction of food intake from 21 to 70 days only, even though followed by ad libitum feedings, resulted in an increase in length of life. The effects of ad libitum feeding early in life were overcome, in part, by the regimen of restriction subsequently imposed. The level of restriction most conducive to an increase in length of life was found to change with age. The rats that were severely restricted in their intake of food throughout postweaning life lived the longest. When the same level of restriction was imposed at later ages, life expectancy progressively decreased; in older rats the duration of life was drastically curtailed. Length of life of older and heavier rats, however, could be extended by restriction of food intake, when the degree of restriction was less severe.