Enhanced thermogenesis during recovery from diet-induced weight gain in the rat.

The present study examined the contribution of energy expenditure to the recovery of body weight after a period of overfeeding. Three groups of 2-mo-old female rats (n = 24) were fed, respectively, a 10% (wt/wt)-fat diet (control), a 35% (wt/wt)-fat diet (high fat) or were force fed 130% of the control diet (tube fed). After 30 days, all groups received the control diet for 18 days of recovery. Both overfeeding protocols significantly increased weight above control levels. This difference disappeared after 7 days of recovery. Increases in resting oxygen consumption, serum 3,5,3'-triiodothyronine (T3) levels, and the thermogenic response to norepinephrine were observed at the end of overfeeding. Serum T3 and resting oxygen consumption returned to control levels by day 3 of recovery from overfeeding, whereas the thermogenic response to norepinephrine required 9 days to recover. Whereas total energy expenditure was not significantly elevated during overfeeding, significant increases of 9.6 and 13.9% were observed in the formerly high-fat and tube-fed animals, respectively, during recovery. These data indicate that changes in energy expenditure play an important role in maintaining the stability of body weight.