Feb. 11, 2008 -- It may sound counterintuitive, but replacing the sugar in diet sodas and other foods with reduced- and no-calorie sweeteners may make weight control harder, a small animal study shows.
Rats in the Purdue University study that were fed regular feed and yogurt sweetened with no-calorie saccharin took in more total calories and gained more weight than rats fed regular feed and yogurt sweetened with sugar.
Researchers speculate that over time, reduced-calorie sweeteners like saccharin, aspartame, and sucralose condition the body to no longer associate sweetness with calories, thereby disrupting its ability to accurately assess caloric intake.
This disruption may, in turn, lead to overeating, they note.
"If this is the case in rats, there is little reason to think that humans don't have this same response," researcher Susan Swithers, PhD tells WebMD. "It is possible that consuming these products interferes with one of the mechanisms that helps to regulate weight."
She adds that this could help explain why the dramatic rise in obesity has occurred at the same time that sales of diet sodas and other products containing low-calorie sweeteners have skyrocketed.
But a spokeswoman for the low-calorie sweetener industry was highly critical of the research, noting that the study involved just 27 rats.
"I think studies like this are a disservice to the consumer because they oversimplify the causes of obesity," registered dietitian Beth Hubrich of the Calorie Control Council tells WebMD.
"It is true that there has been an increase in the use of low-calorie sweeteners at the same time that we have seen an increase in obesity, but there has also been an increase in the use of cell phones and nobody is suggesting that they are causing obesity."
Rats Ate More, Expended Less Energy
The new study is not the first by Swithers and co-researcher Terry L. Davidson, PhD, of the Purdue Digestive Behavior Research Center, to link artificial sweeteners with weight increases in rats.
In a study designed to measure energy expenditure, the saccharin-conditioned rats had slightly lower energy expenditures after eating a high-calorie meal containing sugar.
"In addition to somehow stimulating food intake, we think that artificial sweeteners may blunt the energy expenditure mechanism as well," Swithers says.
Rat Studies Relevant to Humans?
Hubrich counters that it is far from clear if the rat studies have any relevance to people, adding that many human studies suggest low-calorie sweeteners in diet sodas and other foods are beneficial for weight loss.
One of the most recent suggested that use of sucralose -- the sugar substitute sold as Splenda -- along with increased physical activity, helped children lose weight, she says.
"I am not aware of any studies in humans suggesting that the use of low-calorie sweeteners is associated with weight gain," she says.
Clinical psychologist Edward Abramson, PhD, who specializes in treating patients struggling with weight, agrees that rat studies may not have much relevance to humans when it comes to appetite and weight control.
"The issue of food intake and energy expenditure is much more complicated in humans," he says.
But he adds that reduced-calorie sweeteners may trigger overeating in some overweight people, especially those who are binge eaters.
Abramson is a professor emeritus of psychology at California State University and author of the 2005 book Body Intelligence.
"About 30% of obese people are binge eaters, and it may be true that for some eating artificially sweetened foods trigger binges," he says.