Bad Guy #1: Aspartame
There's conflicting evidence regarding the safety of aspartame, a common chemical sweetener used in diet soda and other low-cal or low-sugar goods, but some people report headaches or generally feeling unwell after ingesting anything containing the chemical. To make life easier for everyone, this is one instance where you may want to follow the "better safe than sorry" principle. That's because a University of Liverpool test-tube study found that when mixed with a common food color ingredient, aspartame actually became toxic to brain cells. Making matters worse, aspartame is used in many diet sodas, and studies have found drinking diet soda may increase your risk of developing diabetes and metabolic syndrome. Also of concern with aspartame, researchers have found that one harmful breakdown product is formaldehyde. Sweet? We don't think so.