Casting doubt on the benefit of low-calorie sweeteners, new research released Sunday reported that rats on diets containing saccharin gained more weight than rats given sugary food.

The study in the journal Behavioral Neuroscience found that the artificial sweetener appeared to break the physiological connection between sweet tastes and calories, driving the rats to overeat.

Lyn Steffen, an associate professor of epidemiology at the University of Minnesota, who was not involved in the report, said the study offers a possible explanation for the unexpected association between obesity and diet soda found in recent human studies.

Researchers have puzzled over whether diet soda was a marker for poor eating habits, or whether the ingredients in diet soda caused people to put on pounds, she said.

“This rat study suggests a component of the artificial sweetener may be responsible for the weight gain,” Steffen said.

Steffen’s research resulted in a showing of people who drank diet soda having a higher risk of developing metabolic syndrome, a cluster of symptoms that includes obesity, than people who drank regular soda.