Calorie-conscious consumers who opt for diet sodas may gain more weight than if they drank sugary drinks because of artificial sweeteners contained in the diet sodas, according to a new study. A Purdue University study ... in the journal Behavioral Neuroscience reported that rats on diets containing the artificial sweetener saccharin gained more weight than rats given sugary food, casting doubt on the benefits of low-calorie sweeteners. There's something about diet foods that changes your metabolic limit, your brain chemistry," said ABC News' medical contributor Dr. Marie Savard. Savard said another recent study, which included more than 18,000 people, found healthy adults who consumed at least one diet drink a day could increase their chance for weight gain. In the Purdue study, the rats whose diets contained artificial sweeteners appeared to experience a physiological connection between sweet tastes and calories, which drove them to overeat. "The taste buds taste sweet, but there's no calorie load that comes with it. There's a mismatch here. It seems it changes your brain chemistry in some way," Savard said. The information may come as a surprise to the 59 percent of Americans who consume diet soft drinks, making them the the second-most-popular low-calorie, sugar-free products in the nation. Because so many foods today contain artificial sweeteners, the study results may go beyond diet drinks.