Effect of food restriction on body composition of hereditary obese mice.

T HIS WORK was designed to show the effects of long term dietary restriction on the body composition of obese mice. The animals used were the obese mutants discovered by Ingalls, Dickie and Snell (I), which have since been the subject of extensive studies by Mayer and his colleagues (reviewed in ref. 2). The major anatomical characteristic of the obese mouse is the excess fat or adipose tissue, as indicated in reference 2 and the present study. A few earlier short term experiments on other types of mutant obese mice are relevant to our study. Benedict and Lee (3) fasted obese CHS silver mice; these animals survived 9 days (fasted lean mice survived 5 days). At death, analysis showed a loss of 58% of their body fat but the final value was still five times greater than that of unfasted white lean mice. Their body protein, on the other hand, was only depleted to a final value 80% that of the lean mice. Weitze (4) reduced the daily ration (no values were reported for this restricted food intake) for two yellow obese mice during a period of 8 days. The animals were then killed, and analysis of the carcass indicated a loss of 50% of the body fat. It was concluded that the obese mice can utilize the fat stores. After the completion of our study, Van Putten, Van Bekkum and Querido (5) reported on rats made hyperphagic by hypothalamic lesions, which were given the same amount of food as eaten by lean controls. Despite the lowered food intake, the operated animals had twice the carcass fat concentrations as the non-operated. The experimental design of their study is similar to ours.