Conventional scientific wisdom has been that because artificial sweeteners such as saccharin, aspartame and sucralose do not contain significant amounts of carbohydrates, they are simply ignored by the body’s sugar-regulating functions. Researchers tested this premise by assigning 22 healthy young volunteers of normal weight to fast for several hours, then drink either a diet soda (about two-thirds of a can) or an equivalent amount of carbonated water. Ten minutes later, all participants drank a sugary beverage and their body’s response was measured.

Increases in blood glucose levels were identical in both groups, but participants who had consumed the artificially sweetened drink first showed larger increases in circulating levels of glucagon-like peptide-1 (GLP-1). This hormone, which is released by the gut when food enters the stomach, signals the brain to create the sensation of “fullness.” This reaction has not been observed in people consuming artificial sweeteners on their own.

“Our data demonstrate that artificial sweeteners synergize with glucose to enhance GLP-1 release in healthy volunteers,” the researchers wrote.

The implications of the finding are not clear. Although they appear to suggest that consuming artificially sweetened products might actually cause people to eat less over the long term, previous studies have shown the opposite result. Whether artificial sweeteners produce more fullness, damage the brain’s ability to regulate calorie intake, or produce some more complex reaction remains unknown.

It is becoming increasingly clear, however, that artificial sweeteners do have a significant effect on the body’s reaction to other food.

“In light of the large number of individuals using artificial sweeteners on a daily basis, it appears essential to carefully investigate the associated effects on metabolism and weight,” the researchers wrote.