Indianapolis Star

Cutting sugar might cause weight gain

March 4, 2008

(College of Liberal Arts) -- One of the first steps many people take when they're trying to lose weight is switching to diet soda and artificial sweeteners in their coffee.

But if studies in rats are any indication, such substitutions might actually discourage weight loss. Purdue University researcher Susan Swithers set out to explore why so many more people today than a few generations ago have trouble regulating their weight.

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Swithers, an associate professor of psychological sciences, and her colleagues suspected sweet tastes prime an animal's body to get calories. When no calories are forthcoming -- as happens when an artificial sweetener is consumed -- do those physiological processes work as well?

"Maybe sweet tastes are designed to give us cues for what our bodies are going to experience after we eat them," Swithers says. "Maybe what happens is that animals make this association and produce changes in their physiology to anticipate those calories."

Swithers and her colleagues fed rats yogurt sweetened with glucose, which has the same amount of calories as sugar. Others received yogurt with zero-calorie saccharin.

Rats who ate the artificial sweetener wound up eating more later, consuming more calories and gaining more weight than those fed glucose-sweetened yogurt.

A follow-up study showed it might not just have been the extra calories that contributed to the increased weight gain, but physiological changes.

Researchers measured how rats, some of whom were fed the sugar yogurt and others the saccharin variety, responded to a sweet high-calorie meal. The body temperature in those who ate real sugar rose more than those used to the saccharin. An increase in body temperature correlates with burning off extra calories, Swithers says. So the rats in the saccharin group may have become accustomed to not expect calories when they had something sweet.

"Your body is getting a signal that sometimes a sweet taste means calories and sometimes it doesn't," Swithers says. "From a learning perspective, that's a great way to get an animal to ignore a cue."

While these results have yet to be duplicated in humans, Swithers says it's possible similar forces may be at play. People who use artificial sweeteners and consciously track calories will likely not run into problems, she says. But those who figure they'll just cut out real sugar may be surprised on the scale.