Short-term weight cycling in aging female rats increases rate of weight gain but not body fat content

OBJECTIVE: To examine the effects of short-term repeated weight cycling (WC) above and below the baseline (BL) body weight (BW) on body weight regulation, feeding efficiency, and fat content in old female Wistar rats when dietary fat content was kept constant. DESIGN: Completely randomized. ANIMALS AND METHODS: Female Wistar rats, 11 months old at the beginning of the study, were randomly divided into six groups (12 per group) after a group of rats (BL) was sacrificed for baseline data collection: the high fat gain (HFG) group gained weight to 20% above the BL weight with a high fat diet (HF) and returned to BL level by food restriction (50% of ad-libitum amount) for five cycles; the high fat loss (HFL) group lost weight to 20% below the BL weight by food restriction (50% of ad-libitum amount) and regained to BL level by ad-libitum feeding for four cycles; the high fat ad-libitum (HFA) and low fat ad-libitum (LFA) groups were fed HF and low fat (LF) diet, respectively, ad-libitum for the entire study; the high fat restricted (HFR group) and low fat restricted rats (LFR group) were fed the HF and LF diet, respectively, in restricted amounts to maintain BW at BL level. RESULTS: A trend of increased rates of weight gain and feeding efficiencies from the first to last cycles for both WC groups was observed, and significant increases was observed between cycles 4 and 5. The rate of weight gain and feeding efficiency of HFL was significantly higher than that of the HFG group for all cycles (P < 0.05). The rates of weight loss were significantly decreasing with each successive cycle for HFG, but were unchanged for HFL. Percentage of body fat was not modified permanently from BL to sacrifice for both HFG and HFL groups. The body fat of HFA was higher than that of the other groups (P < 0.01), while the body fat of LFA was significantly higher than that of the LFR, BL and HFL groups (P < 0.01), but was similar to that of the HFG and HFR groups. The body fat of WC groups and HFR were similar to each other. The percentage of internal fat (retroperitoneal + omental) were similar for the WC groups. The percentage of internal fat of the HFG, HFR and LFA groups were similar, but were significantly higher than that of the BL and LFR groups (P < 0.05). The percentage of internal fat of HFA was significantly higher than that of the rest of the groups (P < 0.01). CONCLUSION: Short-term WC did not affect body fat content in these animals, but since weight gain became easier and weight loss became more difficult for animals in the HFG group, repeated WC may promote obesity in these rats.