Sugar-free carbonated beverages, including diet soda and sugar-free flavored sparkling water, can cause problems ranging from headaches to an increased risk of developing diabetes. Although these sugary drinks contain fewer calories than traditional sugar-sweetened beverages, consuming them may contribute to weight gain. Zero-sugar or low-calorie alternatives are usually hundreds or thousands of times sweeter than regular sugar, but they don't raise blood sugar levels. Healthy people may experience mild gas or bloating after eating foods sweetened with sugar alcohols, but if you have a gastrointestinal condition, such as irritable bowel syndrome, or eat a large amount of something sweetened with sugar alcohols, you could experience more extreme symptoms.
A more immediate unpleasant effect of consuming sugar alcohols, a type of low-calorie sugar substitute, are gas, bloating, and diarrhea.