Native to Paraguay, the stevia plant is as much as 300 times sweeter than sugar, but has barely any effect on blood glucose levels and contains no calories.

It's pitched as the 'natural' alternative to artificial sweeteners and is the choice of US physicist and renowned sugar critic, Gary Taubes, who has said that by spiking our insulin levels, sugar, not fat, is responsible for the obesity epidemic and a slew of related illnesses.

In an article for the New York Times, he said stevia "gets my vote as the best noncaloric sweetener, by virtue of being the only one that's truly 'natural'... Extracts of the herb have been used as a sweetener for centuries. In Japan, Stevia has been sold widely as a sugar substitute since the early 1970s without any documented ill effects."

David Gillespie, author of Sweet Poison is more coy about it. In his Sweet Poison Quit Plan book, he puts stevia on the 'your call' list of sweeteners that he believes need more research.

Indeed, concerns have been raised intermittently about stevia over the years. It was questioned in the 70s at the same time that sugar substitutes such as saccharin were suspected carcinogens. Then, in 2008, when the Bush administration gave it the green light, alarm bells starting ringing.

The Centre for Science in the Public Interest issued a statement at the time, saying stevia was "potentially harmful" and that "it is far too soon to allow this substance in the diet sodas and juice drinks consumed by millions of people."

But, for the most part, it's hailed by various health professionals and companies as a natural panacea to sugar's toxic shock to the system.  Even confectionary companies are getting steamed up over stevia. In September, Schweppes Australia launched Pepsi Next. "The new breed of cola... sweetened naturally with stevia," they say. "Used around the world for hundreds of years, stevia is a completely natural sweetener."

But, Dr Alan Barclay, of Diabetes Australia and spokesman for the Dietitians Association of Australia, says stevia may not be quite as natural as the marketing would have us believe.

"There's a little bit of mythology around it," he says. "It took a while to get approved [in 2008 in Australia], now it's the new flavour of the month."

But, he warns, the herb stevia is different from what we see on the supermarket shelf. While he explains the plant extract itself doesn't contain calories, we rarely eat it in its pure form.

The powder "is a highly refined extract, blended with sugar alcohol and... bulked up with maltodextrin [a refined starch that breaks down into glucose]," he says. "To get it table-top sweet, it's bulked out with other carbohydrates which are calorific."

Despite this, Alice Gibson, dietitian with The Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders at the University of Sydney, sees stevia as a good option for people who are watching their weight or calorie intake.

She suggests buying the plant and picking the leaves for a natural tea sweetener. Having said that, she's not sure we need a solution to sugar in the first place. "Sugar is not evil," she says, "if consumed in moderate amounts. If people do consume a lot, they need to look at where it's coming from - fruit or soft drinks... it's looking at your diet as a whole."

She says, as with most foods, the dose makes the poison. "We need sugar, carbs and fat to survive, but above certain levels they are a problem... just because something is naturally derived doesn't mean it is better for us."

Les Copeland, a professor of agriculture at the University of Sydney who specialises in food chemistry, agrees. He also says the added maltodextrin in stevia isn't concerning. "It's pretty neutral... it's produced from starch and is very widely used."

But, stevia is "almost certainly not" a solution to obesity, Copeland says. "There's no magic bullet. There's no such thing. It's taking a holistic approach to diet, looking at portions and also how much you're working it off."

Barclay agrees. It's good to have "consumer choice, so long as people are aware it's not a miracle cure," he says. "Not consuming sugar is not going to make our lifestyle problems go away."

In fact, the move to avoid sugar is creating another set of issues. As with stevia, he says many food producers wanting to appeal to the sugar-fearing public use oligosaccharides (which includes maltodextrin) instead, which do not add nutritional value and can spike a product's glycemic index.

The concern, he says, is that reduced sugar levels are being replaced with highly refined carbohydrates, which, because of a nutritional labelling loophole, do not have to be brought to consumer attention. "These are invisible carbohydrates," he says.

To address this issue, Barclay plans to submit a proposal to Food Standards Australia New Zealand in the next week, recommending "that we deal with carbohydrates on the same level as fat."