Rats fed artificial sweeteners (search) ate three times the calories of rats given sugar, a finding the study's authors said suggests sugar-free foods may play a role in the nation's obesity epidemic.

Other scientists, however, dismissed that conclusion, saying studies on people don't indicate that. One researcher called the rat study nonsense.

The experiment by Purdue University (search) researchers appears in the July issue of the International Journal of Obesity (search). The scientists said their rodent findings could help explain why Americans have grown fatter over the past two decades even as the nation's consumption of artificially sweetened sodas and snack foods has soared.

They contend that artificial sweeteners could be interfering with people's natural ability to regulate how much they eat by distinguishing between high- and low- calorie sweets.

As part of their study, they fed two groups of rats sweet-flavored liquids for 10 days. One group got only sugar-sweetened liquids, while the other was fed liquids sweetened by both sugar and saccharin (search).

After the 10 days, both groups of rats were given a sugary, chocolate-flavored snack and regular rat chow.

Both groups of rats ate about the same amount of the chocolate snack. But the rats fed both sugar and saccharin ate three times the calories of the rat chow than the rats fed only the sugar-sweetened drink.

Susan Swithers, an associate professor of psychological sciences at Purdue, said the findings suggest the rats given the saccharin-sweetened drink ate more rat chow because they experienced an inconsistent relationship between sweet taste and calories.

That, in turn, could confound their natural ability to keep track of calories.

"Consuming artificially sweetened products may interfere with one of the automatic processes our bodies use to regulate calorie intake," said Swithers, the study's co-author.

Adam Drewnowski, director of nutritional sciences at the University of Washington in Seattle, said that whatever caused the rats to overeat is unclear and could have been caused by something other than the sugar-free liquid they were fed. He said the rat results have no bearing on human research.

"They're extrapolating and saying that humans may not be adjusting to the artificial sweeteners because they're expecting calories and the calories are not coming in. I just think this is nonsense," he said.

Drewnowski said a 1994 French study he helped direct compared people given yogurt artificially sweetened with aspartame (search) with people who ate yogurt sweetened with sugar. The study found no differences in eating behavior between the two groups.

Terry Davidson, a Purdue professor of psychological sciences, said the team's findings involving saccharin cannot be extended to more commonly used artificial sweeteners such as aspartame and sucralose, sold as Splenda (search).

G. Harvey Anderson, a professor of nutritional sciences at the University of Toronto who was not involved in the Purdue research, said its findings could be explained by the fact that rats like the taste of saccharin.

He said the rats who overate could have favored the saccharin-flavored drink and then compensated for its lack of calories by eating more rat chow. "I just find this data hard to interpret," Anderson said.