To avoid the calories in sugar， dieters often sweeten foods and drinks with no-calorie substitutes， such as saccharin. But this fake sugar could have unexpected side effects， a new study finds. Its authors show that a high-saccharin diet causes changes in mice and people that could lead to obesity or type Ⅱ diabetes. The sweetener did that by altering microbes in the gut. Other sweeteners would likely cause similar problems， the researchers say.

Until recently， most people thought artificial （no-calorie） sweeteners passed through the body without doing anything. That's what makes them appealing. They add a sweet taste without the caloric cost. Many diet foods， from soft drinks to desserts， are sweetened with these substances. But that may come with a different cost.

To probe the sweeteners' effects， researchers working at the Weizmann Institute of Science in Rehovot Israel， ran tests on mice. The researchers added artificial sweeteners to the animals drinking water. Those sweeteners included saccharin， aspartame and sucralose.

After 11 weeks， the animals showed problems with their metabolism. Unusually high levels of a type of sugar called glucose circulated in their blood after meals. This suggested the sweeteners impaired their bodies ability to process glucose. The most significant problems affected mice that drank water laced with saccharin.Mice that drank water sweetened with glucose had no such problems.

In people， problems with glucose processing have been linked with diabetes and obesity. Being obese raises a person's risk of serious health problems， including diabetes. Diabetes， a metabolic disease， affects how a person turns food into energy. If not well controlled， diabetes can be fatal.