Study: Diet soda doesn't help you lose weight

Diet soda, it turns out, may not be the panacea for weight loss that we all thought — and many of us hoped — it was.

In fact, a Purdue University study has found that diet sodas may be linked to a number of health problems from obesity to diabetes to heart disease, just like their more sugary counterparts.

Susie Swithers, a professor of psychological sciences and a behavioral neuroscientist, reviewed a number of recent studies looking at whether drinking diet soft drinks over the long-term increases the likelihood that a person will overeat, gain weight and then develop other health problems.

One large study found that people who drank artificially sweetened soda were more likely to experience weight gain than those who drank non-diet soda. Others found those who drank diet soda had twice the risk of developing metabolic syndrome, often a precursor to cardiovascular disease, than those who abstained.

Surprisingly, some of the studies suggested diet soda may be just as bad for our health as non-diet.

"Are diet sodas worse for you than regular sodas? I think that's the wrong question," said Swithers, who is also a member of Purdue's Ingestive Behavior Research Center. "It's, 'What good are sodas for you in the first place?' "

The studies included drinks containing aspartame, sucralose and saccharin. About 30 percent of American adults regularly consume these sweeteners.

While research indicating that diet soda might not be a health food has been around a few decades, in the past 25 years, Americans' consumption of these drinks have skyrocketed, among a proliferation of options and concerns over obesity.

Such thinking has driven many schools and hospitals to stop offering sugary sodas in their cafeterias and vending machines in an effort to improve the health of their patrons.

But research, such as that done by Swithers, suggests that tactic could backfire and that there could be serious long-term health consequences to regular consumption of diet sodas.

In scientific terms, Swithers' piece is a review study, one that looks at many different studies to reach a conclusion.

The American Beverage Association, the trade association for the non-alcoholic drinks industry, described it a different way.

"This is an opinion piece not a scientific study," the organization said in an emailed statement. "Low-calorie sweeteners are some of the most studied and reviewed ingredients in the food supply today. They are a safe and an effective tool in weight loss and weight management, according to decades of scientific research and regulatory agencies around the globe."

Many organizations, including the American Diabetes Associationand the Academy of Nutrition and Dietetics, support the use of low- and no-calorie sweeteners to help maintain a healthy weight, the trade industry statement pointed out. In addition, it cited a number of studies that showed that drinking diet beverages will not lead to weight gain or increase a person's desire for sweet foods.

Swithers, whose laboratory research is funded by the National Institutes of Health, disputes that. Her paper appears in Wednesday's issue of the journal "Trends in Endocrinology & Metabolism."

Some studies have shown that when people drink diet soda, they engage in what's known as "cognitive distortion," deciding that since they saved on liquid calories they can splurge elsewhere — the "diet coke and fries" order.

However, something else may be going on. Studies in animals note a link between consuming artificial sweeteners and overeating that leads to weight gain, said Swithers, whose own research relies on animal models. Somehow artificial sweeteners throw off the body's ability to know how many calories it needs.

"We think there's a much more basic fundamental learning process that's getting interrupted," she said.

Normally when someone consumes something sweet, the body expects calories and sugar to follow. But when a person drinks diet soda the payoff never arrives.

"You get this kind of confusion and that can lead to overeating, and at least in the animal model that can lead to an increase in blood sugar spikes," Swithers said.

Of course, diet sodas are not the only places that artificial sweeteners creep into our diets. Some yogurts and baked goods incorporate the no-cal sweet stuff.

Still, there's enough data on diet soda here, she added, for people to act.

"The take-home message is for people to be much mindful of how much sweetener, whether artificial or sugar, they're actually consuming," she said. "We're talking about a health issue here. We're not talking necessarily just about weight gain or weight loss. ... Science suggests that people who drink soda regularly end up with worse outcomes."