Even after his ‘healthy chocolate’ bar had launched in Harvey Nichols, people were still calling Ohso founder Andrew Marten mad. “Everyone said: ‘you’re having a laugh, chocolate can’t be good for you’.”

And yet, four weeks after Ohso’s first meeting with the department store, the first order of the probiotic, gluten-free, no-added-dairy, nut-free Belgian chocolate bars sold out. So did the next two batches. One year on, listings with Ocado and the Tesco-owned Nutri Centre have been secured, and a new flavour - natural orange - is already selling fast. The brand also has fashion fans: it appeared in London Fashion Week goody bags - and subsequently in last month’s Vogue.

Clearly, almost 30 years’ experience in brand development on names such as Wonderbra and Bacardi have paid off for Marten - as has tapping into the ‘healthy chocolate’ trend. In a 2009 survey by the National Confectioners Association, 88% of chocolate industry experts reckoned healthier products would be the next big thing - if a certain hurdle could be overcome. “There’s always been this perception that if it’s good for you, it doesn’t taste good,” concedes Marten. “But we’re the absolute opposite this tastes great, and fits into a healthy lifestyle.”

“There’s always been this perception that if it’s good for you, it doesn’t taste good. But we’re the absolute opposite”

Andrew Marten

Sold in packs of seven individually wrapped bars, weighing in at only 72 calories each, Ohso contains 53% Belgian cocoa, more than a billion “friendly bacteria” and more probiotic goodness than a yoghurt, says Marten, who claims his own digestion noticeably improved after just four days of eating Ohso.

“We discovered the transit of the bacteria through the intestine was three times more effective in chocolate than yoghurt,” he says. “We knew that was an absolute winner.”

If, that is, it is allowed to make the claims. New EU labelling laws came into effect in December restricting the use of the word ‘probiotic’ on packs. Marten says that the message of “friendly bacteria” is becoming broadly accepted, but that the company is currently monitoring the changes and “having to adjust our communication and packaging to comply as necessary”.

Despite the labelling constraints and the fact that sharing bags are fuelling growth at the moment, he is confident Ohso will be able to persuade shoppers and retailers that ‘healthy’ chocolate is what they need. “We’re not competing against Cadbury,” he adds. “We want people who love chocolate to look at this and think, ‘I can still have my chocolate fix but it’s healthier’. Consumers can carry on enjoying their daily bar, in a low-calorie, free-from, probiotic, healthy way.”

Ohso is not just for chocoholics, he adds: Ohso also wants to attract those interested in free-from products. “It’s amazing how many people have a gluten intolerance or problems with lactose,” says Marten.

He’s currently in talks with one retail chain about a listing and several others have been in touch about Ohso appearing on their free-from shelves, he says. “In the past 12 months we’ve spent in the region of £250,000 on marketing and sampling, and that’s going to grow considerably this year,” he adds.

With plans to expand to the US and Hong Kong, new flavours and products in the pipeline, Marten is working hard to maintain “the excitement and the interest”.

Ohso is clearly a little bar of choolate with big ideas - and potentially a big future. Looks like Marten might not be quite so mad after all.