Estrous cycle does not predict food intake in rats on limited access fat option diets

Previous work from our lab indicated that the feeding patterns of male and female rats differed when limited access to fat was provided in addition to a standard diet (1,2). Environmental variables such as season and handling, however, varied between genders in these earlier studies. The present study was designed to determine if the food intake patterns induced by a limited access fat option diet would differ between male and female rats when environmental conditions were the same and if the estrous cycle contributed to these differences. 20 male and 20 female Sprague-Dawley rats were used. All rats had ad lib access to rat chow and water. In addition to the chow and water, 10 rats of each gender were given 2-h access to vegetable shortening on M, W, and F. 2-h and 24-h chow and fat intakes were measured daily. Vaginal smears were taken daily during the last 2 wk to determine estrous phase. Males were similarly handled on the days that smears were taken. Both males and females responded similarly to the limited fat access. That is, on MWF, total 24-h food intake over 4 wk was significantly elevated in the fat option rats (p<0.0001); on T, Th, Sa. S (days that the fat option was not available), food intake was significantly reduced in the fat option rats (p<0.0001). Estrous cycle stage did not predict food intake on the days that the fat was available. These results demonstrate that limited access to fat in the diet can induce excessive intakes independently of estrous cycle stage. 1) Corwin, et al. (1995) Obesity Res. 3: 373s. 2) Dimitriou, et al. (1995) Obesity Res. 3: 373s.