Slimming gurus go to court after celebrity diet is branded fantasy

Two leading French dieticians will slug it out in court tomorrow for the title of lightweight champion of the world.

In the red corner is Dr Pierre Dukan, inventor of a diet which has swept Europe and America and been adopted by celebrities from Jennifer Lopez to Katherine Jenkins. His protein-based diet dismisses calorie-counting and allows slimmers to eat as much as they like of a limited number of things.

In the blue corner is Jean-Michel Cohen, who has hundreds of thousands of followers in France. He says that Dr Dukan's diet is a dangerous re-hashing of old ideas which can increase cholesterol and generate heart problems and breast cancer. He favours a calorie-based diet in which slimmers eat a limited amount of most things (even chocolate) so long as they exercise regularly.

At the heart of the case is an interview given by Dr Cohen to a French health magazine last year. Asked who benefited from the Dukan Diet, Dr Cohen said: "The slimming industry, doctors, pill salesmen, publishers, newspapers... Everyone who has climbed on to the bandwagon of this fantasy."

Dr Dukan is suing Dr Cohen for libel. He claims a modest €15,000 (?13,000) in damages, but tens of millions of euros in book royalties and profits from spin-offs could be at stake. Both men are best-sellers, though Dr Dukan is far more successful. Three of his books were in the top ten French best-sellers last year.

After many years in which his ideas were ignored, Dr Dukan's sales exploded in France three years ago. He claims millions of followers, including singers Jennifer Lopez and Katherine Jenkins. He says that 40 per cent of people who try his diet never regain weight – compared to the standard figure for commercial diet programmes of around 80 per cent.

The Dukan Diet – similar to the Atkins Diet – starts with an "attack" phase where the slimmer sheds weight rapidly by eating only low-fat proteins (from veal to fish to no-fat yoghurts). There are three other phases, which gradually re-introduce vegetables and carbohydrates, but the slimmer must return to the protein-only diet one day a week for the rest of his or her life.

Dukan disciples can eat as much as they want of some of the foods which are permitted. Counting of calories is prohibited. The diet has an almost fetish-like attachment to oat bran.

Dr Cohen's diet allows slimmers to eat anything they like so long as it can be fitted into one of four calorie-based programmes varying from 1,600 calories a day (men) to 900 calories a day (rapid). The idea is to allow individuals to create good eating habits and build their own diets based on likes and dislikes and personal health issues. Neither diet guru is expected to turn up in court for tomorrow's hearing. Dr Dukan's lawyer Sebastié* Dufay says disagreements between doctors are "normal and acceptable but Dr Cohen has gone far beyond mere criticism."

Dr Cohen's lawyer, Richard Malka, says allegations of libel are "ridiculous and abusive". The medical community, he claims, is "unanimous in believing that the Dukan diet carries grave risks... How can it be defamatory to say that diet programmes bring profits to those who publish them?"

Both the Dukan and Cohen approaches – and 13 other diets – were criticised by a recent report by French nutrition watchdog, L'Agence de sécurité sanitaire de l'alimentation (Anses).

All the programmes tested had dangers and weaknesses, Anses said. More than 80 per cent of people who tried book diets put back the weight – or more – the following year. "Slimming makes you fat," said Jean-Michel Lecerf, head of the nutrition service at the Institut Pasteur in Lille. The report said people should ignore "nutritional cacophony" on bookshelves and follow simple rules for a balanced diet.