A 2005 study, by Sharon P. Fowler and colleagues at the University of Texas Health Science Center at San Antonio, showed that people who drink diet soda gain weight - lots of it. In fact, the research found, "There was a 41 percent increase in risk of being overweight for every can or bottle of diet soft drink a person consumes each day."
Some health experts speculate that, while diet soda doesn't cause obesity, people who are starting to put on weight think choosing diet soda alone will stop the process. But, the experts say, this is false logic, because it ignores the true cause of weight gain - overeating and poor eating. "You have to look at what's on your plate, not just what's in your glass," said nutrition expert Leslie Bonci.
Diet drinks aren't diets, she said. "A lot of people say, 'I am drinking a diet soft drink because that is better for me.' But you can't go into a fast-food restaurant and eat a high-calorie, fatty meal and say, 'Oh, it's OK, because I had diet soda.' If you don't do anything else but switch to a diet soft drink, you are not going to lose weight." Also, drinking multiple cans of diet soda every day squeezes out from our diets the healthful beverages - juices, water and teas - that can best benefit our bodies.
Finally, there is still some suspicion - not confirmed - that aspartame, the low-calorie chemical used to sweeten diet sodas, may have some bad health effects. Some animal studies have linked consumption of high quantities of the chemical to brain tumors and lymphoma in rodents. The Food and Drug Administration has certified the sweetener's safety, but reported side effects include dizziness, headaches, diarrhea, memory loss and mood changes.