The turn of a new year is a time of change - but not for the book trade. When 2007 dawns, publishers and booksellers will again be putting all their efforts into pushing the many new diet books which, as surefire hits every January, provide a lifeline when sales of rival tomes are traditionally down.

As the nation faces up to its obesity problem and attempts to slim, the diet-book boom has seen the value of this kind of title more than double in the last four years. In 2002 new diet regimes raked in £7.9m and by 2004 that had risen to £17.9m. This year's figure, calculated only up to 9 December, is a remarkable £12.4m. Booksellers hope the total figure at the end of the year will beat last year's record-breaking £19.8m.

In the summer the Ultimate New York Diet Plan swept the sale charts on both sides of the Atlantic. Devised by personal trainer David Kirsch, it promised a five-inch waist loss in eight weeks. Celebrity clients such as Heidi Klum and actress Liv Tyler were happy to take his advice.

But now an avalanche of new books setting up rival slimming stratagems, complete with their own celebrity endorsements, is making its way onto the bookshop shelves. Each title is aimed at enticing you into parting with your money in exchange for a thinner shape. And 2007, it turns out, is to be the year of the Fairly Sensible Diet. This year's offerings include one that advocates drinking red wine every day, and another which involves having spinach and kale as the 'top choice' ingredients.

As Britain careers on towards its waiting obesity crisis, with more than half the nation now registered as overweight or obese, it might seem that there has never been a better argument for publishers to jump on to the diet bandwagon.

There is Audrey Eyton, founder of the F Plan diet, who, 24 years on, has come up with the F2 Diet, son of F. According to the PR blurb, this harnesses 'unrivalled experience and 21st-century cutting-edge science' to take off the surplus fat faster than any other diet using the same number of calories. Another comparatively sensible regime is put forward in Rick Gallop's Express Gi diet 'for Busy People. It suggests that you should not be looking to lose more than 1lb (half a kilo) a week.

Among the sensible advice on offer, there is some that sounds slightly more fun, such as The Wine Diet, written by a heart specialist, Professor Roger Corder. He wrote it after studying different groups of people from around the world, and looking at the wine people drink in Sardinia, Crete, south-west France and the former Russian republic of Georgia.

For the more ambitious soul, there is the prospect of losing five stone and fitting into a size 12 cocktail dress, which is exactly what writer India Knight and film producer Neris Thomas both achieved on a year-long foray into the world of dieting. The book examines why women overeat.

Doctors are fairly sceptical, but acknowledge that there is a need for good information. Dr Susan Jebb, head of nutrition and health research at the Medical Research Council in Cambridge, said: 'It is positive that so many people want to help themselves to lose weight, and at least realise that they need to do something about it... But we know that the only real diets are the ones that can be sustained over a long period. The problem with a book is that once you've read it, you're on your own.'

The turn away from extreme fads has been noted by Sian Jones, a buyer for Waterstone's. 'Perhaps the danger stories about size zero have brought people to their senses,' she said. 'There is more debate about extreme weight loss. That, in my opinion, should be applauded.'

Battle of the bulge

The Perricone Weight-Loss Diet: Dr Nicholas Perricone

Claims: A three-part programme promising weight loss and reduced wrinkles, Perricone's regime focuses on foods, supplements and exercises that raise the metabolism.

Recommended foods: Cold water fish tops a foods 'super group', with spices, fats and probiotic dairy produce . The doctor orders lots of water and big doses of Omega 3 oils. A precise 14-day diet is included.

Weight loss: Lower weight, and more energy levels are promised in 28 days.

Celebrity fan: Jemma Kidd.

The Japan Diet: Naomi Moriyama and William Doyle

Claims: The Japan Diet claims to change your dietary habits, setting you up for a lifetime of healthy eating in just 30 days. By adopting a Japanese approach - and savouring food slowly - the aim is to avoid hunger. Long-term weight loss is promised.

Recommended foods: Vegetables and fish feature greatly. There are no strict limits on quantity. The ingredients' quality is key.

Weight loss: Expected weight loss is from 1lb (just under half a kg) to 2lb a week.

The F2 Diet: Audrey Eyton

Claims: Writer of the best selling F-Plan Diet, Eyton has formulated 'a faster, more effective' version. No fuss' tactics banish hunger pangs, fat dissolves fast and good bacteria is multiplied. Results are promised within days.

Recommended foods: Homemade soups are the integral part of the F2 Diet, as are fruit, vegetables and pulses. Daily meal plans, detail fat units and calorific content.

Weight loss: Bloating greatly cut in 48 hours. 'I've lost a stone in just a month,' claims dieter Mary Clarke.

Express Gi Diet for Busy People: Rick Gallop

Claims: Gallop has honed his Gi regime to meet the 'needs of a hectic lifestyle'. Foods are colour-coded in accordance with what you should and should not eat to lose weight. 'Green light' foods have the lowest glycaemic index, and are digested slowly, preventing hunger and promoting weight loss.

Recommended foods: pulses, soya milk, seafood, oatmeal.

Weight loss: Averaging 1lb a week, or 2lb for those a lot overweight.

Celebrity fans: Kylie Minogue, Kim Cattrall.

The Wine Diet: Roger Corder

Claims: Professor Roger Corder answers drinkers' prayers with a diet that praises the health benefits of a moderate daily consumption of red wine. Corder's priority is to achieve a healthier lifestyle, but he believes weight loss will happen naturally as part of his plan.

Recommended foods: With chocolate still on the agenda, lists of hearty recipes and a wine guide, this is a happy way to slim.

Weight loss: Corder rejects crash dieting in favour of a change in eating habits. Expect slow but permanent results.

Neris and India's Idiot-Proof Diet: India Knight and Neris Thomas

Claims: Written by two friends wanting to lose 10 stone between them in 12 months, this reads like a diary and explains our relationships with food.

Recommended foods: Knight and Thomas spurn 'impossible exercise' and 'disgusting things to eat', focusing on the high-protein, low-carb principle and lots of water to drink.

Weight loss: Both writers succeeded. Knight quickly dropped two dress sizes.

· Compiled by Martha Alexander