A naturally-sourced sugar substitute called stevia apparently has no calories, no carbohydrates, and does not raise blood sugar levels. Is it too good to be true?
Mention "stevia" to someone and you may well get a quizzical look, as if you're failing to grasp some unknown language.
But stevia - a plant used as a sweetener for centuries in Paraguay and Brazil - can now be found in many British supermarkets. In the US, it's even more common.
It has been heralded as a "miracle sweetener" and the "holy grail for the food industry", because of its natural origins and claimed health benefits.
Although stevia has been sold in Japan for about 40 years, stevia-based products have only been approved as a food additive since 2008 in the US, and 2011 in the EU.
Companies have been quick to capitalise. There was a 400% increase globally in new stevia-based products between 2008 and 2012, with a 158 per cent rise from 2011-2012, according to Mintel.
"The big deal about stevia is that it has a natural source," says food writer and TV presenter Stefan Gates. "That doesn't mean it isn't incredibly highly processed by the time it gets into your drink or food… but that's what everyone is craving."
British vitamin retail chain Holland & Barrett says it has witnessed a 50% sales rise for stevia products in the last four weeks, compared with the same period last year.
Coca-Cola dared to alter the recipe for Sprite in the UK, re-launching a new stevia-inspired version in March and claiming a 30% calorie reduction.
Even sugar giant Tate & Lyle has responded with a sugar-stevia hybrid. You can now find stevia-based sweeteners in products as varied as yoghurts, chocolates, and even beer, says Mintel's global food and drinks analyst David Turner.
Refined sugar is now regularly linked in the media to obesity. And obesity is now widely described as an epidemic.
More than 60% of adults in the UK are overweight or obese, with associated health problems costing the NHS an estimated £5bn annually, according to the latest government statistics.
Stevia has the potential to help with weight management, dental health, and diabetes, says Dr Laura Wyness, senior nutrition scientist at the British Nutrition Foundation.
Stevia is extracted from the stevia plant in a similar process to sugar, says Dr Margaret Ashwell, who is on the scientific advisory board of the Global Stevia Institute.
"The extraction process involves steeping the dried leaves of the plant, like you would tea, and then separating or purifying the best tasting sweet compounds, which are known as steviol glycosides."
The concentrated extracts are about 300 times as sweet as sugar.
The steviol glycosides remain intact and chemically unchanged throughout the whole process, she says.
In contrast, artificial synthetic sweeteners such as aspartame - used in soft drinks like Diet Coke - have long been the subject of controversy.
