Five-week-old male, Osborne-Mendel rats were fed a control (CON) or high fat diet (HF) (18 and 68% calories as fat, respectively). At 15 weeks of age HF rats weighed more and had a greater percent body fat than CON rats. Half the rats in each diet group were then exercised for 6 weeks on a treadmill. During exercise, food intake was unaffected in both diet groups, while body weight gain was reduced only in HF rats compared to sedentary rats. Exercise lowered fat gain and decreased lipoprotein lipase (LPL) activity in all rats, reduced in vivo lipogenesis in CON rats, and attenuated the development of obesity in HF rats. Following exercise, rats were kept inactive (i.e., detrained) for 2 weeks. Detraining increased food intake, weight gain, fat deposition and LPL activity in comparison to sedentary rats. In CON detrained rats lipogenesis returned to sedentary levels; in all detrained rats retroperitoneal fat cell number increased over that found in exercised rats. Thus, HF feeding induced obesity while exercise attenuated its development. Exercise-induced effects were not long lasting as they were reversed within 2 weeks of exercise termination as evidenced by a rapid increase in food intake, weight gain and lipogenesis.

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