Soft drinks: It's not just the bottle that'll have a nipped-in waist

Fresh from the supermarket shelves of the world's most enduringly inventive country, a truly revolutionary concept – Pepsi that is not only low fat, but actually stops other foods from making you fat.

The high-fibre Pepsi Special went on sale in Japan yesterday. It contains the wheat dextrin, a so-called "fat blocker", and has even won a stamp of approval from the Japanese government, whose National Institute of Health and Nutrition class it "food for specialised health use".

But hold your horses Nobel Prize committee! The body that conducted one of the few confirmed tests of dextrin was none other than… Japan's National Institute of Health. Its 2006 study found that rats that ate dextrin absorbed less fat from their food than rats that didn't – which is all well and good, but dextrin works through aiding the movement of food through your bowels. Similar effects have been observed after eating such outlandish things as nuts. Or fruit.

High-fibre or not, soda is still soda and though figures for the sugar content of Pepsi Special have not been released, dieticians are sceptical. Nevertheless, a similar product already on sale in Japan – Kirin's Mets Cola – has been a big seller this summer among the slimming and the gullible – so Pepsi can be assured that they are on to a good thing.

Dextrin, meanwhile, the secret ingredient that will make you slim (probably), is a natural soluble fibre that is already popular in the US, where it is the active ingredient of dietary supplement Benefiber – a company whose clever conflation of the words "beneficial" and "fiber" is only slightly tainted by the product's safety guidance, which states that Benefiber is "generally well-tolerated". Not really the sales pitch you'd want to put on a soft drink advert.

Sarah Kirk, senior scientist at the MRC Human Nutrition Research institute, was not impressed by Pepsi Special. "Dressing something unhealthy with something that makes it look healthier does not cut it. Soft drinks are adding calories to our diet with no health benefit. Adding this doesn't make it better – at best it makes it less bad."

There is no news yet about whether we can expect to see Pepsi Special on these shores. Pepsi's Japanese distributor, Suntory, has a record of releasing intriguing riffs of the popular brand that – for better or worse – have never crossed the Sea of Japan.

More fool us for missing out on the unbeatable tastes of Pepsi Pink, Pepsi Ice Cucumber, and of course, Pepsi Salty Watermelon.