By The Numbers: The Truth Behind Those Scary Diet-Soda Myths

What is it about diet soda that seems so naughty? Maybe it's because enjoying something without any calories leads people to feel like they're going to have to pay one way or another-if not with their waistline now, then with ambiguous bad health later (a tumor? osteoporosis?). Maybe it's because it takes an already unnatural beverage-there's no such thing as a soda tree-and fills it with even more foreign substances. Either way, people often have a complex, love-hate relationship with diet soda, especially when you throw some caffeine into the mix.

But it's not good to fear your food. And while as adults we can eat whatever we want, it's also nice to know what it is we're eating. With that in mind, we set out to find the truth behind the biggest diet-soda myths.

Myth: The artificial sweeteners will give you cancer.
Reality: Comprehensive reviews of the literature have not uncovered any reason the sweeteners should have carcinogenic effects. "There's no known negative biological pathway," says Barry Popkin, professor of nutrition at the University of North Carolina and author of The World Is Fat (Avery 2008). . "In none of the major sweeteners in the U.S. and Europe is there any major evidence that these sweeteners are harmful, even if you look to the top thousandth of a percent of users," he said, meaning those who drink the most soda.

Myth: Artificial sweeteners are OK. It's the caffeine that's a problem.
Reality: Hardly. A Diet Coke has 46.5mg of caffeine per 12-ounce can, and a Diet Pepsi has 36. (A seven-ounce cup of coffee, by comparison, has anywhere from 85 to 135mg of caffeine.) "For most people, up to 300mg a day of caffeine seems to be safe," says nutritionist Elisa Zied, spokesperson for the American Dietetic Association and author of So What Can I Eat? (Wiley 2007) She does say that certain medications and heart conditions may make that much caffeine a bad idea, so check with your doctor or pharmacist if you're unsure.

Myth: The bubbles in soda will make your bones brittle.
There has been research that links diet-cola consumption with increased risk for osteoporosis in women, but it doesn't have to do with the carbonation. The main ingredient in any cola-diet, regular, caffeine-free-is phosphoric acid, a flavor agent that increases the acidity of the blood. (While mostly found in cola, some other sodas have it as well, so check the label.) "At that point, your body's first priority is to restore a balance, so it leaches some calcium out of your bones to neutralize the acid," says Katherine Tucker, a senior scientist and director of the dietary assessment and epidemiology research program at Tufts University. She found that three or more colas a week lead to significant bone-density loss in women, and that a cola a day leads to even more dramatic loss.

Tucker would rather recommend homemade iced tea as a beverage alternative. "It's calorie-free, and there are lots of good phytonutrients," she explains. But she theorizes that drinking diet cola at the same time as you eat foods high in potassium, another neutralizing agent, could help-though it hasn't been tested. That means a Diet Coke downed while eating a lunch full of vegetables and whole grains could be better for your bones than the can you drank at your desk instead of breakfast.

Myth: Drinking diet soda causes you to gain weight.
Reality: This one is tricky-it's called diet soda for a reason, right? And yet epidemiological research often associates diet soda with weight gain-like 2005 study from the University of Texas Health Science Center, which showed that with each diet soda a person drank there was a 41 percent increase in the likelihood of becoming obese over the next seven to eight years. These larger epidemiological studies, however, measure correlation more than causation, meaning that the soda isn't necessarily what's leading to the weight gain. It could be the other way around: people may start drinking diet soda when they start gaining weight.

In a separate longitudinal study, researchers found that those who drank diet soda were more likely to have metabolic syndrome, a nasty cluster of diseases including diabetes, obesity and high blood pressure. The study didn't define a definite reason for this-and can't say for sure that one causes the other-but tried to control for other factors, like preexisting health problems, says Dr. Ramachandran Vasan, study author and professor of medicine at Boston University School of Medicine. It's possible that people may use diet soda as an excuse to eat poorly (the old "two Big Macs and a Diet Coke" approach) or that there may be some sort of biological pathway in diet soda that causes these problems.

Research in mice has led to interesting theories about the effects of artificial sweeteners on weight. "In animal studies, giving them small quantities over a couple of weeks leads to a small but statistically significant increase of body weight gain," says Susan Swithers, a psychologist at Purdue University's Ingestive Behavior Research Center. That may be because the body associates sweetness with calorie intake, and when one eats something sweet, the body prepares for an increase in calories. When those calories don't come, the body gets confused-which could lead to a slowing of metabolism or a craving for more food to offset the perceived loss.

Will diet soda alone turn you from a svelte size 4 to a curvier 14? Will the addition of diet soda to your day make you drop two sizes? No-especially if you're not already drinking full-calorie beverages (there has been some studies that show swapping out regular soda for diet can lead to statistically significant weight loss).

The Last Word
It's important to look at the bigger picture. "You need to look at the soda consumption in the context of your entire diet and the rest of your lifestyle," says Zied. Is a daily Diet Coke your one indulgence in an otherwise spotless nutritional lineup? Or does it complement your morning Snickers and substitute for your afternoon lunch? If diet soda is just one symptom of your overall unhealthy eating habits, it's time to make a change. If it's a treat you enjoy on occasion, you're probably fine. And if it's a daily comfort you don't want to live without, that's your choice to make. The most damning indictment of diet soda is the calcium loss-something that, if you're addicted to diet soda, could theoretically be offset with proper nutrition and fitness habits (weight-bearing exercises can increase bone density).

So if the only thing keeping you from enjoying an ice-cold glass of Diet Sprite on occasion is the fear that the "diet" part must somehow imply something bad and wrong, give in to temptation. It may not make you healthier, but it won't kill you, either.

Photo: afiler