There may be a good reason why some studies these days show that females have more of a problem with obesity than males.
According to new research, females are more likely to yield to their sweet tooth than males, and they are less likely to be able to work off those extra calories. At least if they are rats. And probably if they are humans.
Psychologists Lisa A. Eckel and Shelley R. Moore of Florida State University in Tallahassee wanted to know if women are disadvantaged when it comes to controlling their weight, as several recent studies have suggested.
So they gathered up a bunch of male and female rats to see if they could induce them to overeat, a condition called hyperphagia. That turned out to be pretty easy. All they had to do to get the rats to pig out was add a little sweet milk to their regular lab chow. Both males and females found the sweeter chow more to their liking.
But that's pretty much where the similarity ended.
When the sweet chow was available, the females ate a lot more than the males. And they were far less likely than the males to spend enough time on an exercise wheel to work off those calories.
So the female rats suffered a one-two punch: They ate more if the meals were palatable, and they exercised less after eating sweets. And furthermore, the exercise wasn't as helpful for the females as it was for the males.
It can't be said for certain that the same applies to humans, but Eckel says the research certainly suggests that's the case.
"The story just keeps getting worse for women," she says.
The researchers reported their findings in a recent issue of the American Journal of Physiology — Regulatory, Integrative and Comparative Physiology. Eckel says they set out on the project because recent studies show the "rates of obesity are greater in women than in men, so it seems like something is regulating the energy balance equation, making it more difficult for women than men" to control their weight.
In an ideal world, people would have been better subjects to study, but she notes that human experiments are much more difficult to control. You can't keep humans in cages for long periods of time, carefully regulating their diet and exercise. But you can do that with rats.
And while it isn't always the case, what's true for rats can also be true for humans.
In the experiment, rats were fed regular "lab chow," as the researchers put it, and sometimes they were given chow with sweet milk. Sometimes, the rats had access to an exercise wheel, and sometimes they didn't. That allowed the researchers to see gender differences in both eating and exercising.
One difference surfaced immediately. When the rats were denied access to the exercise wheel, the males ate more than the females.
When the wheel was available, both males and females ate less if they exercised, but there was a big difference between the sexes when the diet was sweet.
"We found that the females exercised less when they were given access to the sweet diet," Eckel says.
And the time spent on the wheel didn't do much to curb their appetites. "The caloric intake reduction associated with the exercise was much less dramatic in the females," the researchers report.
That suggests the sweet tooth is more powerful in females than in males, and all that sugar leaves them less likely — and less able — to work it off. But why should that be the case?
Eckel says she doesn't know for sure, but the research suggests that the female hormone estrogen may be at work here.
"Female rats, just like women, have higher levels of estrogen than men," she says, and other research has indicated that estrogen can increase the preference for sweets.
"The take home message is, at this point, we think it may be related to the major sex hormone secreted by women, and it may be that this particular hormone increases our desire to eat sweets," Eckel says.
The complete answer isn't known, she adds, because research on overeating has been "almost exclusively on males."
So for now, if what holds true for rats also works for humans, women have more of a struggle against obesity than men because, well, they are women.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.