(This article previously appeared on Grandparents.com.)

Each week, a new study seems to pop up linking a diet soda habit with increased risk of obesity, diabetes, heart disease and other bad things.

The latest study, presented at the American College of Cardiology's annual scientific meeting, found that older women who drank two or more diet sodas a day, compared to older women who rarely or never drank them, were 30 percent more likely to have a cardiovascular "event," such as a heart attack. The study looked at 60,000 women (average age 63) over nearly nine years. No wonder Diet Coke sales dropped nearly 7 percent last year.

Devil in a can? Beelzebub in a bottle? Actually, that's far from proven.

These studies show association, not cause. And not all studies find harm.

At the Harvard School of Public Health, for example, researchers report no association between diet soda and weight gain, diabetes or heart disease. Says Vasanti Malik, a research associate at the nutrition department of the Harvard School of Public Health: "The verdict is still out on long-term health consequences of diet soda consumption."

(MORE: Is Diet Soda Making Us Gain Weight?)

So is diet soda to blame for serious heath risks? Truth is, we just don't know — yet.

It's hard to reach conclusions between people with weight problems (and often, metabolic diseases such as heart disease and diabetes) since these people tend to drink more diet sodas because they're trying to lose weight. It may be that the obesity is "causing" the diet soda consumption, not the other way around.

In the most recent heart disease and women study, for example, "it is likely that the women who started drinking more diet soda may have had other health issues/concerns or family medical conditions related to cardiovascular health that caused their switch," says Shu Wen Ng, assistant professor of nutrition at the Gillings School of Public Health at the University of North Carolina.

But here's the thing: Even cautious scientists such as Malik thinks it's a good idea to drink less diet soda — and, ideally, none at all. "They should be consumed in moderation," she says. "They can be helpful in transitioning people away from regular soda to more healthy beverages such as sparkling water — which should be the ultimate goal."

Sweet Dangers

Before we look at diet sodas, let's remember why we turned to them in the first place: to replace regular soda and sugary drinks.

There's nothing in the current controversy that makes drinking sugar-laden soda or lemonade or energy drinks any safer. Sugary soft drinks are a major contributor to obesity and obesity-related diseases. One recent scientific review concluded that "intake of free sugars and sugar-sweetened beverages is a determinant of body weight."

In that context, switching to diet soda seemed logical. If sugar is a major contributor to weight gain, wouldn't switching to no-sugar beverages help? But it hasn't. And there are reasons to be concerned about diet soda:

Metabolic problems. Artificial sweeteners signal to your body that it is consuming something sweet. That stimulates hormones, including insulin, to spike — and, since there's no sugar to digest, to stay high. Some researchers, such as behavioral neuroscientist Susan Swithers, of Purdue University, believe this "metabolic confusion" increases the risk of disease such as diabetes. It's not proven, but it's a concern.

Artificial sweeteners signal to your body that it is consuming something sweet. That stimulates hormones, including insulin, to spike — and, since there's no sugar to digest, to stay high. Some researchers, such as behavioral neuroscientist Susan Swithers, of Purdue University, believe this "metabolic confusion" increases the risk of disease such as diabetes. It's not proven, but it's a concern. Overstimulated overeating. These intense artifical sweeteners — between 200 and 300 times sweeter than sugar — may increase appetite, says Malik. That sweetness causes your body to expect calories but when none arrive, there's nothing to satisfy that appetite. So you stay hungry. And eat more. "We're not sure how artificial sweeteners stimulate the brain, but there may be expectations of sweetness that are never quite satisfied," says Boston-based nutritionist and author Elizabeth Ward.

These intense artifical sweeteners — between 200 and 300 times sweeter than sugar — may increase appetite, says Malik. That sweetness causes your body to expect calories but when none arrive, there's nothing to satisfy that appetite. So you stay hungry. And eat more. "We're not sure how artificial sweeteners stimulate the brain, but there may be expectations of sweetness that are never quite satisfied," says Boston-based nutritionist and author Elizabeth Ward. The "I'm dieting" trap. Research at the University of North Carolina has found that people who consume a large amount of diet sodas tend to fall in one of two camps — the careful dieters, and the fast food crowd. The first group drinks diet sodas, but also "prudent" snacks and low-calorie desserts. For this group, it's possible that diet sodas can play a useful role in controlling calories. The other group drinks diet sodas but also lots of ready-to-eat meals and fast food. "It's the Big Mac, large fries and diet Coke phenomenon," says Ng. If that describes you, drinking a diet soda may just be giving you a false "health halo" that gives you permission to eat unhealthy food. Just because you drink a diet soda doesn't give you carte blanche to eat a big pizza and a large bowl of ice cream.

So while diet soft drinks may not be pure poison, there's good reason to limit your intake — and start to work them out of your diet.

"A can of diet soda once a week is fine," says Ng, "but I wouldn't have one every day." Not only is there the potential for harm, but there's also no actual proven benefit to drinking diet soda.

(MORE: What Alcohol Can You Drink While Dieting?)

Harvard's Malik believes we should think of diet sodas like products we use to quit smoking — as a way to step down from our excessive reliance on sweetness.

"You can think of diet soda as a nicotine patch of sorts when trying to kick the habit of consuming regular soda," she says. The ultimate goal for health is to drink none. Says Ng: "All in all, the best recommendation is to drink water — zero calories, no additives."

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