Nutrition and Longevity in the Rat

Abstract

Restriction of food intake of rats to levels 33 and 46% below the ad libitum level, from weaning to 800 days of age, resulted in 5 to 7% reduction in tibia length, 6 to 13% reduction in body length, and 25 to 40% reduction in body weight. The difference in body weight was due largely to absence of excess body fat which developed in unrestricted animals. The latter ate more than they needed to meet energy output. Health and female fertility were better in rats kept on dietary restriction than in unrestricted rats attaining maximum size. In accord with Huxley's principle of heterogony, measurements of tibia length and body length of rats on restricted food intake were proportional, and linear plots gave points falling on the same straight line as the corresponding measurements of animals fed ad libitum. There was no significant difference in skeletal size of unrestricted rats caged singly or together. However, food intake and male body weight were slightly lower in singly-caged animals. Differences in body weight at the time of weaning continued through adult life in rats that were fed ad libitum. The proximal epiphysis of the tibia of 800-day-old rats on restricted food intake showed no evidence of osteogenesis and had the same microscopic appearance as the epiphyseal cartilage of unrestricted rats of the same age. Food utilization was more efficient in males than in females. Skeletal measurements and body weight were greater in males on 33% restriction than in unrestricted females on the same food intake. The body weight of males on 46% restriction was equal to that of unrestricted females but skeletal measurements were greater.