The Purdue University scientists believe the fake sugar in diet sodas teases your body by pretending to give it real food. But when your body doesn't get the things it expects, it becomes confused on how to respond. On a physiological level, they say, this means when diet soda drinkers consume real sugar, the body doesn't release the hormone that regulates blood sugar and blood pressure.
Basically, the healthiest people are those who eat a healthy diet and have limited their intake of any type of sweetener, Popkin said. But if you have a sweet tooth, that may be a hard sell.
So how much is too much?
The FDA recommends ingesting no more than 50 milligrams of aspartame per kilogram of body weight every day. That amounts to 22 cans of diet soda for a 175-pound man, and 15 cans for a 120-pound woman. If you're putting two packets of artificial sugar into coffee, that would be about 116 cups of coffee for the man in this example, and 79 cups for the woman.
"I really think that if you are consuming five or six cans a day, you may have more problems from consuming too much caffeine or acid than from the sweeteners," Walters said.
No large, controlled studies have shown that there is a limit to how much diet soda you can consume without harm if you're keeping the rest of your diet in check, Popkin said. So far, at least, human research has not shown that quantity of artificial sweetener matters.
"It's not whether it's 2 or 6 or 10," Popkin said. "It's a question of what else they do with their diet that counts."
As with most things in life, artificial sweeteners aren't dangerous in moderation.
Researchers will continue seeking answers to these questions and CNN will continue to report on the latest findings, in pursuit of the soda fountain of youth.