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Atlanta, GA - Is stevia, an extract 300 times more potent than sugar, the no-fat, no-calorie "natural" sweetener that soda and juice lovers have been thirsting for?

Since the Food and Drug Administration approved the use of rebaudioside A (Reb A) as a general purpose sweetener in December, major beverage marketers have been rushing new stevia-infused drinks into stores. Coca-Cola is using the stevia-derived sweetener Truvia in two of its Odwalla juice drinks and in the new Sprite Green. PepsiCo added its version of stevia to Sobe Lifewater drinks and has launched a new Tropicana orange juice, Trop50, containing 50 percent less sugar and calories.

The sweetener, which manufacturers claim is natural because it’s derived from the leaf of a South American shrub, has been used for years as a commercial sweetener in Japan and other Asian countries. It’s too soon to know whether American consumers will lap up its slightly licorice-y flavor, but nutritionists are already weighing in with their own verdict: Stevia is no risk-free holy grail for dieters.

Certainly, there's plenty to worry about when it comes to how many calories we guzzle each day. A recent study by researchers at Louisiana State University's School of Public Health found that liquid calories are a bigger problem than food when it comes to weight gain, and that sugar-sweetened beverages are the main culprit. What's worse, Americans consume an average of 20 teaspoons of added sugars a day, about twice as much as recommended, according to government reports.

But so far, there’s nothing to distinguish stevia from other sugar substitutes on the market, despite its boast about being natural, nutrition experts say. Stevia may have no calories, but you shouldn't make it a regular dietary staple, says New York City-based nutritionist Keri Gans, a spokesperson for the American Dietetic Association.

“Given our nation’s problem with obesity, stevia and other artificial sweeteners have a place for people who consume more calories than they should from sweets,” says Gans. “But artificial sweeteners should not take over your diet because that means you’re eating way too many processed foods.”

Back to nature?

Marketers counter that that stevia is as natural as sugar, despite a “purification” process that modifies the plant extract.

“Truvia is still all natural,” says Coca-Cola spokesman Ray Crockett. “It’s the same process cane sugar goes through.”

The new stevia extract is the only widely marketed sugar substitute derived from a shrub. Other commonly used sweeteners aspartame (Nutrasweet, Equal) and saccharin were developed artificially in labs. Sucralose (Splenda) is derived from sugar but is processed with chlorinated chemicals.

Just as cancer concerns have dogged the artificial sweeteners aspartame and saccharin, some researchers worry about stevia. In fact, the FDA rejected stevia petitions in the 1990s after research linked the plant with infertility in rats and cancer in the lab. The agency says the currently marketed reformulation, Reb A, is “generally recognized as safe.”

Chemistry researcher John Pezzuto isn’t convinced. He cites a study he conducted that suggests a certain strain of stevia can mutate DNA, a possible cancer risk.

“Given that there’s the potential for a mutagenic response, why take the risk with stevia?” asks Pezzuto, dean of the University of Hawaii at Hilo College of Pharmacy. “I will not be consuming any myself.”

However, another researcher, genetic toxicologist David Brusick dismisses Pezzuto’s findings.

“That was an in vitro test, done out of the mainstream of tests,” says Brusick, an independent consultant formerly with biopharmaceutical drug development company Covance Laboratories in Vienna, Va. “Studies in animals and people have found no such mutagenic effects.”

Brusick reached his conclusions after reviewing studies for the FDA’s stevia approval. Stevia-associated companies had hired him to conduct the evaluation.

Sticky problem with sweeteners

While nothing's been proved as far as cancer risks, there's a more immediate catch when it comes to stevia. Critics wonder whether it may also stoke hunger, just like other artificial sweeteners.

Studies indicate that consuming something with a sweet taste primes the body for a calorie delivery that doesn’t happen. As a result eaters seek more sweets to satisfy the body's cravings. Recent research also found that sucralose may alter people’s gut bugs in ways that promote weight gain.

None of these metabolic questions have yet been explored with stevia, according to experts.

While rats only develop such problems after ingesting large quantities of these sweeteners, it's not unexpected that at least some people would overindulge with with stevia-sweetened products, notes Orlando-based nutritionist Tara Gidus, spokesperson for the American Dietetic Association.

While nutritionists agree that Americans consume too much sugar, the real sweet stuff isn't entirely the problem. It’s how much sugar we consume that leads to obesity, diabetes and other related ills.

And when it comes to our drinks, maybe we should simply learn to crave beverages that don't need to be highly sweetened. “When it comes down to what people drink regularly, I recommend low-fat milk, seltzer or water over soda every time,” says Gans.