Kidney Problems: In an 11-year-long Harvard Medical School study of more than 3,000 women, researchers found that diet cola is associated with a two-fold increased risk for kidney decline. Kidney function started declining when women drank more than two sodas a day. Even more interesting: Since kidney decline was not associated with sugar-sweetened sodas, researchers suspect that the diet sweeteners are responsible.

Messed-Up Metabolism: According to a 2008 University of Minnesota study of almost 10,000 adults, even just one diet soda a day is linked to a 34 percent higher risk of metabolic syndrome, the group of symptoms including belly fat and high cholesterol that puts you at risk for heart disease.

Obesity: Diet soda doesn't help you lose weight after all. A University of Texas Health Science Center study found that the more diet sodas a person drank, the greater their risk of becoming overweight. Downing just two or more cans a day increased waistlines by 500 percent. Why? Artificial sweeteners can disrupt the body's natural ability to regulate calorie intake based on the sweetness of foods, suggested an animal study from Purdue University. That means people who consume diet foods might be more likely to overeat, because your body is being tricked into thinking it's eating sugar, and you crave more.

A Terrible Hangover: Cocktails made with diet soda get you drunker, faster, according to a study out of the Royal Adelaide Hospital in Australia. That's because sugar-free mixers allow liquor to enter your bloodstream much quicker than those with sugar, leaving you with a bigger buzz.

Cell Damage: Diet sodas contain something many regular sodas don't: mold inhibitors. They go by the names sodium benzoate or potassium benzoate, and they're in nearly all diet sodas. But many regular sodas, such as Coke and Pepsi, don't contain this preservative. That's bad news for diet drinkers. These chemicals have the ability to cause severe damage to DNA in the mitochondria to the point that they totally inactivate it - they knock it out altogether. The preservative has also been linked to hives, asthma, and other allergic conditions. Since then, some companies have phased out sodium benzoate. Diet Coke and Diet Pepsi have replaced it with another preservative.

Rotting Teeth: With a pH of 3.2, diet soda is very acidic. The acid is what readily dissolves enamel, and just because a soda is diet doesn't make it acid-light. Adults who drink three or more sodas a day have worse dental health.

Reproductive Issues: Sometimes, the vessel for your beverage is just as harmful. Diet or not, soft drink cans are coated with the endocrine disruptor bisphenol A (BPA), which has been linked to everything from heart disease to obesity to reproductive problems.