Long-term weight cycling reduces body weight and fat free mass, but not fat mass in female Wistar rats.

OBJECTIVE: The effects of repeated weight gain and loss, the weight cycling (WC) phenomenon, on body composition have been controversial. WC history and age are two confounding factors which may contribute to this inconsistency. In the present investigation, we examined the effects of WC on body weight regulation, body composition and feeding efficiency in a long-term study when WC history was controlled.
METHOD: Six groups of female Wistar rats were used in this study. Five of these six groups were made obese by feeding a high fat (HF) diet for 11 weeks and then divided into five groups: non-cycling control group (HFCON); one group which cycled three times (HFCYC); and three one-cycle groups which cycled only once corresponding to each of the three cycles in the HFCYC group. The sixth group was fed the low fat diet without cycling (LFCON). Weight cycling (WC) was produced by feeding 50% of a HF diet with extra protein, vitamin and mineral mixture until body weight of the cycled groups reached the level of the LFCON group. After three cycles (52-56 weeks), all rats were killed.
RESULTS: Results showed that repeated WC reduced final body weight and fat free mass, but not body fat mass in the HFCYC group. Repeated WC also reduced rate of weight regain. During the third cycle, the amount of fat regained during refeeding was more than the fat mass lost during restricted feeding in the HFCYC group. For the three one-cycle groups, the rate of weight regain was slower but rate of weight loss was the same in older rats as in the younger rats.
CONCLUSION: Thus repeated WC may favor more body fat retention in later cycles. Aging affected rate of weight regain but not rate of weight loss, nor body composition, while repeated WC affected both rate of weight loss and regain.