Isoflavone reduces body weight by decreasing food intake in ovariectomized rats.

Background/aims: The primary objective of this study was to further determine the mechanisms by which isoflavone prevents obesity induced by ovariectomy.

Methods: Female 8-week-old Wistar rats were randomly assigned to 6 groups: a sham-operated group; an ovariectomized (OVX) control group; 3 OVX groups orally administered 400 ppm (L-SI), 1,200 ppm (M-SI) and 3,600 ppm (H-SI) of an isoflavone preparation, respectively, and an OVX group receiving 0.45 ppm of diethylstilbestrol. All animals were allowed free access to a high-fat diet and water for 4 weeks. Some neuropeptides, including ghrelin, neuropeptide Y (NPY), alpha-melanocyte-stimulating hormone (alpha-MSH), cholecystokinin (CCK), peptide YY (PYY), insulin and estradiol (E2), were measured by radioimmunoassay.

Results: Compared with the OVX control group, body weight, total abdominal fat, food intake and food availability of the M-SI and H-SI groups were significantly reduced. The results also showed that isoflavone and diethylstilbestrol could decrease ghrelin and NPY levels and increase CCK, PYY and E2 levels. The level of alpha-MSH was not changed.

Conclusions: These findings showed that isoflavone could reduce obesity by decreasing food intake, possibly by (1) reducing ghrelin and NPY levels, thereby decreasing food intake, and (2) increasing CCK and PYY levels, which can induce satiety by irritating the vagal center.