Fat is a celebrity issue

It's the "the no-hunger, luxurious weight-loss plan that really works!" according to the book's cover blurb. And Geri Halliwell and Catherine Zeta Jones are among the stick-thin celebrities that swear by it. After 10 million-odd worldwide sales, Dr Robert Atkins's New Diet Revolution is still riding high in the bestseller lists. But while the popularity of this high-protein, low-carbohydrate diet has spawned a host of similar weight-loss programmes, complete with celebrity fans – the Zone (Brad Pitt, Renée Zellweger), Sugar Busters (Sharon Stone, Tori Spelling) – it is also now provoking a fierce medical row.

A group of US doctors, the Physicians' Committee for Responsible Medicine (PCRM), has launched a campaign warning of long-term health risks associated with Atkins's regime, and of possible legal action against doctors who recommend it. And the group's campaign has the backing of a number of British dietary experts.

The theory behind Atkins's diet is that carbohydrates encourage the body to produce insulin, which in turn causes fat. Cut out the carbs, says the good doctor, and the body starts to burn its own fat for fuel – effectively eating itself – and rendering you skinnier, faster. This process is known as ketosis, and its side-effects are nausea, bad breath but also, handily, a loss of appetite.

A typical, meat-heavy "induction" menu might include eggs and bacon for breakfast, a cheeseburger for lunch (no bun) and prawn cocktail followed by steak for dinner.

Dr Wendy Doyle of the British Dietetic Association is among those who just don't swallow the "wonder diet" claims. "I think there is evidence to prove that this diet is dangerous," she says. "You're cutting out fibre, which is important for your gut's health; its deficient in nutrients; and you're eating a lot of saturated fat, which is associated with increased cholesterol levels. I think the PCRM's campaign is a very useful early warning to the medical profession."

The president of the PCRM, Neal Barnard, says: "The Atkins diet is exactly the sort of diet you would give someone if you wanted to give them colon cancer, kidney disease, heart disease or osteoporosis... Numerous health bodies, including the American Heart Association, have been objecting to the diet since it first came out. It doesn't make you lose weight any faster than you would on any other kind of diet, and Atkins has never published any peer-reviewed papers to back his claims."

Barnard is encouraging those who have suffered adverse reactions to the diet to share them on PCRM's website. And there does seem to be plenty of anecdotal evidence to suggest that, despite its word-of-mouth success, the diet doesn't agree with everyone.

"It made me so ill that I will never go near it again... I still have headaches," writes "a reader from the UK" in the customer reviews section of Amazon.co.uk. "While I did lose weight, I suffered for it," writes another, "by the end of the week I was a half-crazed wreck."

In response to these criticisms, Colette Heimowitz, the director of education and research for Atkins Health and Medical Information Services, comes out fighting. "With 40 years experience as a clinician, if Dr Atkins was killing people it would have been evident by now," she says, adding that there is no research to prove the diet causes any health problems. Controversially, she dismisses "the old hypothesis that low fat equals lower heart disease. It has yet to be proved, after billions of dollars of research." Indeed, a wealth of new evidence, she claims, shows that the Atkins diet actually improves the condition of your arteries – as some fats lower "bad" cholesterol levels. As for the charge of nutritional deficiencies, well, you need to take vitamin supplements with any diet, she says.

While the idea that doctors may be sued for promoting Dr Atkins diet is described by Heimowitz as "preposterous", the jibes about his lack of published research do appear to have hit home. The doctor last year established the Atkins Foundation, a non-profit-making body that, Heimowitz says, will be funding dietary studies at the Albert Einstein School of Medicine.

Whatever evidence is unearthed there will add to a growing mountain of contradictory studies. In fact, the whole subject is confusing enough to send the average dieter reaching for a comforting packet of chocolate biscuits. Especially if one takes on board the nastier claims that Atkins and the PCRM have been making about each other. According to the former, the PCRM is really "an extremist vegetarian animal rights group" – something Barnard denies, although he does admit that his organisation's agenda is in part informed by the ethical treatment of animals. On the counter-attack, Barnard refers to the eyebrows raised in the dietary world when Atkins, 71, suffered a cardiac arrest earlier this year – Atkins himself claims it was brought on by an infection and "in no way related to diet". Muddying the water further, both Atkins and PCRM have at one time or another been censored by the American Medical Association – although both parties say this simply shows they are not afraid to challenge received medical wisdom.

One attempt to cut through the fat, so to speak, and take a balanced, objective view of the available evidence on high-protein diets has been undertaken by Dieticians in Obesity Management UK. Its latest report finds there is "some evidence of improved speed and quantity of weight loss" with such diets but that this is largely as a result of greater fluid loss than with their high-carbohydrate equivalents.

It also talks of "potential detrimental effects on bone density and other longer-term nutrition related problems". And, while there are possible benefits in manipulating the protein-carbohydrate balance in our diets, "more long-term studies are required".

The group's chair, Dympna Pearson, says: "We have to be careful about giving people simplistic messages. What is important is a balanced diet, which includes carbohydrates. The reason why people lose weight with Atkins is because they stop eating the things they used to. Ketosis stops people from feeling hungry." It's a view echoed by Dr Wendy Doyle: "It's the number of calories you take in compared to the number of calories that you use that determines the success of a diet, and there are more calories in a gram of fat and protein than in carbohydrate."

Perhaps this really is the crux of the matter. Forget all the medical in-fighting, the celebrity fads – even the earnest recommendations of friends. There's only one useful piece of advice if you want to lose weight: eat less. Simple, really... isn't it?