Abstract
It has been previously reported that in rats undergoing repeated weight gain/loss cycles, more fat is regained than that was lost. Conjugated linoleic acid (CLA), a collective name for a mixture of positional and geometrical isomers of linoleic acid, is known to regulate body composition by decreasing body fat. The present study was designed to examine the effects of CLA on body fat regain in weight-reduced obese rats. Female Wistar rats (n=52), 6 mo old, were divided into 4 groups: 1) HFRF rats (n=10) were fed a high fat diet (40% w w ) diet for 9 weeks to an obese state and were then food restricted (50% ad-lib) with a modified high fat diet for 3 weeks to induce a 20% body weight loss. They were then refed the high fat diet ad-lib for 8 weeks; 2) HFCL rats (n=22) were treated in the same manner as rats in HFRF except were refed a high fat diet with 1% CLA ( w w ); 3) LFCN rats (n=10) were fed regular rodent diet ad-lib; 4) HFCN rats (n=10) were fed a high fat diet ad-lib. Ten HFCL rats were sacrificed after 4 weeks of refeeding while body composition and plasma glucose and insulin assessed for the other groups as a comparison. All remaining rats were sacrificed after 8 weeks of refeeding. After 4 weeks of refeeding, HFCL rats were similar in both body weight and body fat %. At the end of the study, HFCL rats weighed the same as high fat fed rats while HFRF rats weighed the same as rats of the other groups. All high fat fed groups had significantly higher % body fat than low fat fed rats but were not different from each other (HFCL: 22 ± 2%; HFRF: 23 ± 2%; HFCN: 27 ± 2%; LFCN: 15 ± 2%). HFCL and HFCN rats had significantly higher retroperitoneal lipoprotein lipase activity levels than that of HFRF rats (p<0.05). HFRF and HFCL rats had similar plasma insulin, leptin, and estradiol levels at sacrifice. HFCL rats had significantly lower IGF-1 levels (p<0.05) than that of HFRF and HFCN rats, while LFCN rats had levels similar to all groups (nmol/L, HFCL: 10 ± 0.7; HFRF: 13 ± 0.8; HFCN: 13 ± 0.8; LFCN: 11 ± 1.7). We conclude that a 40% high fat diet with 1% CLA fed to weight-reduced obese rats did not prevent the fat regain during the refeeding phase. The previously reported anticarcinogenic effect of CLA reported by other investigators may be partially due to lowered IGF-1 levels without the alteration of other hormone levels.
Published Version
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