Female cats rapidly increase food intake following ovariectomy. Because the increased intake is not matched with an equal increase in energy expenditure, the result is an increase in body fat mass. This study investigated whether administration of estradiol or genistein (an isoflavone in soy products) would 1) prevent an increase in food intake following gonadectomy of male and female cats and 2) prevent an increase in body fat mass. Sixteen intact domestic shorthair cats (8 males and 8 females), aged 12 to 16 months, were surgically neutered before the study. Cats (8) in the estradiol group were injected subcutaneously with 0.5 µg estradiol in 100 µl sesame oil. Cats (8) in the genistein group were administered the product orally as a powder in gelatin capsules at a dose of 100 mg/kg. Eight cats were used as controls. Food intake at the end of the study was greater for the control and genistein-treated cats than for the estradiol-treated cats, indicating a significant treatment effect on food intake after gonadectomy. With regard to weight gain, there was a significant treatment effect with the estradiol group-that group gained significantly less weight than the control group. However, there was no significant change in body weight between the control and genistein-treated groups. The results of this study thus demonstrate that administration of estradiol can ameliorate the increased food intake commonly seen in cats following gonadectomy. Oral genistein appeared to be effective in preventing adipogenesis and was associated with a preferential increase in lean body mass after gonadectomy.

COMMENTARY: This study confirmed the effects of neutering, which increases food intake and weight gain when cats are fed ad libitum. Another important finding is that estrogen replacement prevented nearly all of this increase and that the phytoestrogen genistein significantly reduced body fat accumulation. Genistein, a soy isoflavone, also promoted an increase in lean body mass. Lean body mass drives basal energy expenditure, so increased lean body mass may contribute to reduced obesity. These results are similar to those of prior research with soy isoflavones in dogs, suggesting a possible benefit from supplemental phytoestrogens, or diets containing phytoestrogens, to help reduce obesity in neutered pets. -- Dottie Laflamme, DVM, PhD, Diplomate ACVN

Oestradiol, but not genistein, inhibits the rise in food intake following gonadectomy in cats, but genistein is associated with an increase in lean body mass. Cave NJ, Backus RC, Marks SL, Klasing KC. J ANIM PHYSIOL ANIM NUTR 91:400-410, 2007.