Animal Studies of Estradiol and Food Intake
Animal research in rats has clearly linked estradiol levels to food intake. In contrast to the highly stable daily feeding patterns of male rats, female rats' food intake varies dramatically during the ovarian cycle.[2,3] During estrus, food intake -- and weight -- declines. The overall decline in food intake is attributable to a decrease in the size of meals consumed (Fig. 1) rather than a decrease in the eating frequency. The number of meals may actually increase, but rarely enough to offset the decrease in meal size. Food intake may increase during metestrus, again because of a change in meal size. Finally, body weight usually decreases by a few grams during estrus.
Figure 1. Decrease in food intake during estrus in non-oophorectomized cycling female rats. Data are mean size (left) and number (right) of spontaneous meals in 7 rats during typical 4-day ovarian cycle.
Oophorectomy leads immediately to absence of physiologic and behavioral estrus, loss of the ovarian rhythm of eating, and an increase in the basal level of food intake[2,3] (Fig. 2). The increase in food intake leads to an increase in body weight of about 25% over 3 to 5 weeks, mainly because of an increase in adiposity. Food intake then decreases, and weight stabilizes at 25% higher than pre-oophorectomy weight. Oophorectomy-induced hyperphagia is solely attributable to a large increase in meal size. The initial weight increase abates only because the animals gradually reduce the daily frequency of eating. The increased meal size following oophorectomy appears to be related to a lack of estradiol. Cyclic replacement of estradiol is sufficient to reinstate the normal level and rhythmic pattern of food intake. Some metabolites of estradiol act similarly, but much less potently.
Figure 2. Mean daily food intake in 7 female rats before and after oophorectomy.  Before oophorectomy, spontaneous food intake was decreased on days of estrus. After oophorectomy, food intake increased dramatically and rhythmic decrease was lost.
Progesterone replacement leads to reinstatement of sexual receptivity in oophorectomized female rats but does not result in a return to normal eating. Progesterone alone fails to affect feeding, metabolic fuel utilization, or body weight in oophorectomized rats, although large doses may antagonize the effects of estradiol.[2,3] Other ovarian hormones and gonadotropins have not been reported to affect eating behaviors. These data suggest that estradiol is also likely to control the decrease in spontaneous meal size during estrus, but this has not been proven.
Medscape General Medicine. 1998;1(3) © 1998
Cite this: The Effect of Estrogen on Appetite - Medscape - Nov 19, 1998.