Sep. 24, 2004 BETHESDA, Md. – It is well known that obesity has reached epidemic proportions. As waistbands expand, so do the number of health gurus heralding the benefits of portion control and exercise to keep obesity at bay. But with some studies indicating that the rate of obesity is greater in women than in men, could it be that women are at a disadvantage when it comes to these obesity avoidance tactics? Is it possible that females are predisposed to succumb to the temptation to overeat? And could exercise be a less effective method of appetite suppression in women than in men? Researchers at The Florida State University say the answer could be yes.
Overeating (hyperphagia) and sedentary behavior are known risk factors for obesity, but research in these areas – especially overeating – has been studied almost exclusively in males. In the new animal study “Diet-induced hyperphagia in the rat is influenced by sex and exercise,” Lisa A. Eckel and Shelley R. Moore (The Florida State University Program in Neuroscience and Department of Psychology) found that:
* rats overate when given access to a highly palatable diet containing a greater portion of sugar than their normal diet
* when a sweet diet is freely available, female rats consumed more calories per day than male rats
* when given a chance to exercise, overeating was reduced in both sexes of rats, but
* the caloric intake reduction associated with the exercise was much less dramatic in the female rats, and
* unlike male rats, female rats exercised less when sweet foods were available than when sweet foods were not available.
The researchers concluded that female rats are more susceptible than male rats to over consume a palatable, sweetened diet, and that female rats are less likely than male rats to use exercise as a means to control appetite in the presence of such a diet.
The results of their study were published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology (August 5, 2004 Article in Press).
Rats increased their caloric intake when fed a diet containing greater fat or sugar than that found in regular laboratory chow. Because such diet-induced hyperphagia has been studied primarily in sedentary male rats, the researchers’ goal was to investigate the effects of gender and exercise on caloric intake of a diet (chow supplemented with a supply of liquid sweetened condensed milk), chosen for its ability to stimulate hyperphagia. Rats were housed individually in cages that provided access to running wheels. Daily caloric intake of chow alone and then chow plus sweet milk was monitored during sedentary and active conditions.
In sedentary rats (where the running wheel was blocked), chow intake was greater in males, compared to females. In other phases, wheel running produced similar decreases in chow intake in both sexes. Availability of the chow plus milk diet increased caloric intake, compared to that observed in chow-fed rats. This diet-induced hyperphagia was significantly greater in sedentary females (35.7 ± 3.1% increase), relative to sedentary males (9.1 ± 2.2% increase).
Wheel running decreased intake of the chow plus milk diet in both sexes. In active males, diet-induced hyperphagia was abolished and caloric intake was reduced to that observed during chow feeding. In active female rats, diet-induced hyperphagia was attenuated, but not abolished, and caloric intake of the chow plus milk diet remained greater than that observed during chow feeding. The researchers’ conclude that female rats are more vulnerable than male rats to this “sweet” form of diet-induced hyperphagia.
Source: The article “Diet-induced hyperphagia in the rat is influenced by sex and exercise” is online in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, and is scheduled to appear in the November issue, published by the American Physiological Society. A copy of the abstract is available to the public at http://www.the-aps.org.
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