People who use an artificial sweetener may be at greater risk of obesity than those who use normal sugar, American scientists warned yesterday. Researchers raised concerns after experiments with animals showed they ate more food and put on more fat if saccharin was part of their diet. The researchers believe that zero-calorie artificial sweeteners may disrupt the body's ability to associate sweet tastes with high calories. This could make it harder for people to regulate their food intake, so they over-eat.

Susan Swithers and Terry Davidson at the Ingestive Behaviour Research Centre at Purdue University in Indiana took two groups of rats and fed them low-fat yogurt. One group received yogurt with saccharin, while the other consumed yogurt sweetened with natural glucose.

They found that animals that had saccharin continued eating for longer. Those taking the artificial sweetener also showed a lower rise in body temperature, a sign that their metabolism was not firing up as much. "The data clearly indicate that consuming a food sweetened with no-calorie saccharin can lead to greater body weight gain and adiposity than would consuming the same food sweetened with a high-calorie sugar," the authors write in the journal Behavioural Neuroscience.

Previous studies into the effects of sweeteners have been inconclusive, with various studies showing weight loss, weight gain or little difference.