According to Professor Michael Lean from the University of Glasgow, globally every year, obese people waste billions of pounds on food products that 'imply' that they aid weight loss, which are actually totally ineffective.

Professor Lean says the distinction between medicines and foods is sometimes unclear when they are marketed for health reasons and consumers can be misled and he hopes that a new European Union (EU) Directive on Unfair Commercial Practices, adopted this year in UK, will offer protection to vulnerable consumers who are tricked into buying useless food products or supplements in attempts to combat their disease.

Food products that are marketed for health reasons are not subject to the same stringent research trials and control that drugs are subjected to and consumers are all too often misled.

While it is already illegal for unsubstantiated claims to be made about the composition or nutritional function of food products, (that they are low in fat, high in fibre or help lower cholesterol) it is also illegal to claim that a food can treat or prevent any disease - including obesity.

But despite this many unsubstantiated health claims are still made, or implied, and marketing which is misleading can be found on brand names, images, packaging, and on shelf or shop names and on websites which suggest that the products help weight control, are slimming, or are "health foods", when there is no evidence to support such claims.

Professor Lean says he is concerned that obese people have been fooled into parting with billions every year on products that cannot help them - in 2000, people in the U.S. spent $35bn ( 22bn) on weight loss products, many of them making false and unsubstantiated claims.

Professor Lean hopes the commercial exploitation of vulnerable patients with 'quack medicines' will be brought to an end with the introduction of the new EU directive, but he also suggests the laws will need to be enforced proactively to enable doctors and consumers to move towards managing diseases confidently with evidence based treatment and diet programmes.

Professor Lean says of all the hundreds of products currently on sale to help people lose weight, only energy-restricted diets and exercise, the drugs orlistat and sibutramine, and in some cases bariatric surgery, are safe, effective and cost-effective - the remainder, he says, are either not effective or not safe.

Professor Lean says the new regulations may possibly even help with the wider battle of preventing obesity, by prohibiting advertisements across the EU that encourage children to buy energy dense products and demand that their parents buy them.

Professor Lean's article appears in the British Medical Journal.