Food deprivation-induced activity in dietary obese, dietary lean, and normal-weight rats

Dietary obesity and dietary leanness were produced in adult male rats by feeding them either an assortment of palatable foods, or an unpalatable quinine-adulterated diet. When deprived of food the dietary obese rats initially showed little change in wheel running activity but as their weight fell to below normal levels they displayed a terminal burst of activity similar to that seen in normal-weight control subjects. Dietary lean rats, on the other hand, increased their wheel running activity at an accelerated rate, relative to normal-weight controls, when food deprived. Expressing the activity data as a function of percentage normal body weight eliminated these group differences. The results demonstrate that body weight must fall to some relatively fixed, i.e., diet independent, critical level before activity increases during a fast. Therefore, as measured by deprivation-induced activity, dietary obese, dietary lean, and normal-weight rats do not equally defend their particular weight levels.