Scientific studies suggest you should probably lay off the sugar-packed Big Gulp.
But what about their zero-calorie counterparts?
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"There is this cultural lore that has people thinking that diet soda is what's really bad for you and that the other stuff (sugar-sweetened soda) isn't as bad," said Harold Goldstein of the California Center for Public Health Advocacy. Worries include that artificially sweetened drinks will cause cancer or diabetes.
Though most science dissuades drinking regular soda, diet soda's comparatively ambiguous research has not completely dispelled the lore.
Here are answers, some rather nuanced, to common questions about diet soda.
Is diet soda poisonous?
No, it won't poison you.
Most diet sodas are made with artificial sweeteners such as aspartame, which are several hundred times sweeter than real sugar or high-fructose corn syrup. Because not much of these are needed, a diet soda can get away with negligible calories.
Artificial sweeteners "have probably been the most intensively studied food ingredient ever," said Richard Mattes, professor of foods and nutrition at Purdue University. "Every panel has cleared them."
Does diet soda make me eat more?
Barry Popkin, professor of nutrition at the University of North Carolina at Chapel Hill, said the big question is whether drinking diet beverages "means you'll eat more sweet foods."
There is some evidence that suggests so. Several years ago, Susan Swithers, professor of psychological sciences at Purdue, gave one group of rats a consistent diet of pudding with sugar, and another group pudding with artificial sweeteners.
She then fed all the rats a real-sugar snack. At the next meal, rats with the diets of artificial sweeteners ate more than those with a sugar diet.
"They were used to getting sweet-tasting stuff that didn't give them as many calories," Swithers said.
Animal research like this "helps us to understand what might happen in humans," but is not the whole story, said David Allison, nutrition professor at the University of Alabama at Birmingham. Lab conditions may be unrealistic, and there are big size and cognitive differences between rats and people.
Will diet soda make me gain weight or get Type 2 diabetes?
To determine whether these findings have long-term implications, over decades scientists have followed the diets, lifestyles and health of large groups of people.
In some of these "observational studies," statistics have shown that drinking diet soda might increase risk for weight gain, heart attacks or diabetes.
But others show no effect.
Why doesn't science seem to have the answer?
Allison explained the inconsistent results.
"When you look across studies, what you see is that it's always a different analysis."
Relationships might also be misinterpreted, he said. If a study showed a relationship between headaches and aspirin use, "it would be foolish to conclude that aspirin causes headaches."
Analogously, people who drink diet soda might be heavier, but it may be because they are drinking diet soda as part of an effort to lose weight.
What does science know?
Not surprisingly, overall diet and health are important.
Lawrence de Koning, nutrition researcher at the Harvard School of Public Health, studied diet soda's relationship with Type 2 diabetes.
When he accounted for underlying risk factors, such as a participant having high cholesterol, "the apparent relationship between diet soda and Type 2 diabetes disappeared." (It remained for regular soda.)
Should I drink diet instead of regular?
"There's more and more rock-solid evidence that sugary drinks are the leading contributor to the obesity epidemic," Goldstein said.
The average American drinks about 42 pounds of sugar every year, he said.
"That's how much my 5-year-old weighs."
"In some ways the question of diet soda is a compelling one, but it's also a bit of a distraction," he said.
So, research is ambiguous, but diet soda seems the wiser choice, especially if you monitor overall diet.