Drinking no−calorie sweeteners may actually make it harder for people to control their calorie intake and body weight according to a new study.

For this study, psychologists at Purdue University's Ingestive Behavior Research Center used modern science's favorite human substitute — rats. They gave one group of rats yogurt sweetened with glucose (a simple sugar with 15 calories/teaspoon, the same as table sugar), and another group yogurt sweetened with zero−calorie saccharin. Then they watched, as the no−cal sweetener group ate more, gained more weight and put on more body fat.

Interestingly, these findings match emerging evidence that people who drink more diet drinks are at higher risk for obesity and metabolic syndrome...

Reporting these findings in the February issue of Behavioral Neuroscience, authors Susan Swithers, PhD, and Terry Davidson, PhD, speculate that by breaking the connection between a sweet flavor and high−calorie food, the use of saccharin inteferes with the body's ability to regulate calorie intake. Problems with this internal self−regulation mechanism might be one reason why human obesity has risen along with our use of artificial sweeteners. It might also explain why previous studies of artificial sweeteners have been strangely inconclusive, with some studies finding evidence of weight loss, others finding weight gain and still others finding little effect.

The experimenters also measured changes in the rats' core body temperature. Normally when rats — or humans — eat, the metabolic engine revs up. However, rats that had been using saccharin showed a smaller rise in core body temperature after eating a sweet−tasting, high−calorie meal. The authors think this blunted response led to overeating and made it harder to burn off calories.

"The data clearly indicate that consuming a food sweetened with no−calorie saccharin can lead to greater body−weight gain than would consuming the same food sweetened with a higher−calorie sugar," the authors write. Interestingly, these findings match emerging evidence that people who drink more diet drinks are at higher risk for obesity and metabolic syndrome, a collection of medical problems such as abdominal fat, high blood pressure and insulin resistance that puts people at risk for heart disease and diabetes.

The good news, Swithers says, is that people can still count calories to regulate intake and body weight. However, counting calories may require more effort than simply replacing high−calorie with low−calorie foods. It may actually require eating less.