esearchers at the Purdue University in Indiana found that artificial sweeteners might contribute more to weight gain than food rich in sugar.

“What the results suggest is that consuming artificially sweetened products by themselves may not in fact contribute to weight loss - and to the contrary, may sometimes lead to weight gain,” Dr. Susan Swithers , a professor of psychological sciences at Purdue University and co-leader of the experiment said.

The researchers base their theory on an experiment they made on laboratory rats. They gave different yoghurt to different groups of rats, some sweetened with sugar and some with saccharine. The rats were given a plentiful supply of food.

The researchers discovered that rats fed on yoghurt sweetened with saccharine ate more calories, gained more weight and put on more body fat than rats that were given yoghurt sweetened with glucose. Dr. Swithers and her colleague Dr.Terry Davidson who also led the study, have suggested that breaking the connection between a sweet sensation and high-calorie food, the use of saccharine changes the body’s ability to regulate how many calories it consumes.

“The data clearly indicate that consuming a food sweetened with no-calorie saccharine can lead to greater body-weight gain and adiposity than would consume the same food sweetened with a higher-calorie sugar,” they concluded in their report, which is published in the Journal Behavioral Neuroscience.

Moreover, the researchers discovered that the artificial sweetener caused a biological change in the rats, slowing down their metabolism. According to them, when your body takes something sweet, your metabolism revs up to start burning off the calories that usually follow.

But when the calories just aren’t there, your body could get confused. And the next time you do take in real sugar, your metabolic response may not kick in.

The study used saccharin, but the researchers believe the principle applies to other sweeteners as well. They also admit that their results might not be welcomed by nutritionists and doctors who have long recommended low-calorie or no-calorie sweeteners.

Dr. Swithers also notes that other human studies have already shown a similar effect. A University of Texas Health Science Center survey in 2005 found that people who drink diet soft drinks may actually gain weight; in that study, for every can of diet soda people consumed each day, there was a 41% increased risk of being overweight.

The British Nutrition Foundation said the findings were “interesting.” However, they did not prove that artificial sweeteners could be counterproductive in dieting humans.

“This needs far more research – as studies in humans have shown that low-calorie sweeteners can help people lose weight,” a spokesperson for the BHF said quoted by BBC News.

In America, the number of people who eat foods containing sugar-free sweeteners has doubled from 20 years ago to about 160 million. For the same time frame, obesity among adult Americans climbed up by 30 percent from only 15 percent.