There's no such thing as a free lunch, or at least a free artificially sweetened one, a new study suggests. Saccharin and other artificial sweeteners may raise blood sugar levels—a condition the sugar substitutes aim to help prevent—by altering digestive bacteria, Israeli researchers reported on Wednesday. (Related: "What Lives in Your Gut?")

Sugar-free sodas and diet snacks abound with artificial sweeteners, invented more than a century ago as a cheaper sugar substitute. Amid an obesity epidemic, the U.S. Food and Drug Administration has to date approved six artificial sweeteners, which are widely used and roughly 500 times sweeter than sugar. These additives cut calories from foods and drinks, and are seen as precluding the elevated blood sugar, or