One Purdue study in particular found that even though these sweeteners don't contain calories, they cause weight gain in animals. The researchers speculate that the intense sweetness tricks the brain into thinking that calories are on their way when they aren't! The body gets confused, slows metabolism, and ramps up appetite. This imbalance in regulating calories leads to overeating.
Also, artificial sweeteners are often found in combination with sugar alcohols such as maltitol, sorbitol, glycerol, xylitol, isomalt, and mannitol, among others. Sugar alcohols, which offer sweetness but do not get absorbed, are designed to replace table sugar. Because these molecules technically are not digested, they can linger in the digestive tract for a longer period of time and cause stomach upset in people with sensitive tummies or who consume excessive sugar alcohols.