The effects of exercise and food restriction on obesity and diabetes in young ob/ob mice.

Hormone levels and body composition were examined in six-week-old C57BL/6J ob/ob mice following 25 d of limited caloric intake, voluntary exercise, or combined treatment. Pair-feeding obese mice to the daily intakes of lean mice reduced body weight gain, skeletal growth and lean body mass. Although weight gain was the same in the two phenotypes, ob/ob mice had fourfold higher rates of fat deposition. When exercise was combined with pair-feeding, skeletal and lean body growth were reduced even further and weight gain was now less than ad libitum-fed lean controls. Carcass fat accretion, however, continued to be two to three times greater. No single treatment reversed the hyperglycemia or elevated hormone production of obese mice, although slightly lower values of glucose, insulin, glucagon and corticosterone were associated with pair-feeding. When diet was combined with exercise, fasting glycemia and glucagonemia were reduced to equal the values of lean mice but insulin and corticosterone levels remained elevated. The present results show that dieted and exercised ob/ob mice continue to exhibit very high rates of fat deposition even though skeletal and lean growth are severely limited. Since fat accretion is maintained under these conditions, it appears that obese mice are not just storing excess calories as fat, but are actively regulating body fat content to levels about 30 percent higher than lean mice.