Lifesmart: Get the Facts, Follow the Steps, Feel the Difference
by Carole Caplin
192pp, Weidenfeld, £16.99

French Women Don't Get Fat: The Secret of Eating for Pleasure
by Mireille Guiliano
280pp, Chatto, £12

The GL Diet
by Nigel Denby
252pp, Blake Publishing, £7.99

How you respond to Lifesmart, a book designed by the nation's most famous "lifestyle guru", Carole Caplin, to encourage us to take a holistic approach to our mental and physical health, depends on two things. First, whether you can use the words "lifestyle guru" without quotation marks and second, whether you can read lines such as "interaction of energy enables the depleted energy of the patient to benefit from the energy radiated by or through the healer", or references to cells moving "in the direction of life" or bad times as "a golden opportunity to catch up with you" without vomiting into the nearest bucket.

If you can't, exposure to Lifesmart could result in permanent damage to your oesophagus. It cleaves tightly to such alternative therapies as Autonomic Response Testing (involving muscle-testing, colour therapy and judicious tapping of the energy meridians to determine illness and treatment), Electronic Gem Therapy ("gemstones are reservoirs of pure radiating energy [whose] rays pass through the body and influence cellular behaviour in a similar way to infrared rays"), magnet therapy and many, many more.

Some of Caplin's basic premises and advice are sound - no one, for example, would disagree that good nutrition is vital for good health, that we should eat a balanced diet and organically wherever possible, that childhood training affects us in later life, or that orthodox medicine is weaker on preventing disease than it is on curing it.

But these molecules of common sense and demonstrable fact are all but undetectable in the ocean of nonsense that surrounds them. In addition to its advocacy of alternative treatments and new age language, the book is awash with the kind of sweeping statements and authoritative assertions that should rouse the suspicions of any attentive reader about the conclusions he or she is being asked to draw and the quality of evidence adduced for them. In the first chapter, Caplin relates how a few decades ago, medical experts and public health agencies advised people not to eat butter because saturated fat was bad for them. Margarine, made from hydrogenated fat, was then developed and sold as a healthier alternative. Now they are realising that trans-fatty acids in hydrogenated fat can contribute to heart disease and people are being advised to return to butter. This is meant to shore up her claim that public authorities are not to be trusted. But it could more plausibly be argued that the authorities gave the best advice they could based on the knowledge available at the time, and that when that knowledge was superseded they reacted accordingly. Would that all alternative practitioners did the same, instead of explaining away their lack of results by "patient resistance" or insufficiently sophisticated methods of measuring outcomes.

Caplin also uses the old scaremongering trick of listing every possible side effect of prescription drugs, from mood swings to liver failure to hallucinations, without pointing out that not all of them apply to all the drugs previously mentioned, that some of the effects are vanishingly rare (but noted by the orthodox medical community as part of their quest to keep themselves and their patients as fully informed as possible), and that some are worth the trade-off for the benefits their drugs bring to those suffering serious conditions.

It's an infelicitous elision that perhaps alone wouldn't matter, but it must be added to numerous other jarring moments that cumulatively taint the book: there is illogicality ("our personalities are partly inherited from one or both of our parents", for example, when they must be from both if at all), there is an unhelpful absence of distinction ("junk food, junk chemicals and junk pharmaceutical drugs"), and there is often a sense that Caplin has got carried away with her mission to enlighten and inform, leading to overheated, meaningless non sequiturs. "Did you know that the glue for papier mache is made of flour and water? Just imagine what bread can do to your digestive tract," she writes, during her damnation of gluten. Such a combination should cast doubt on the wisdom of allowing her to hold forth on more serious subjects such as the immunisation/autism debate, as she does in the opening chapter. I would also question the morality of claiming that mothers' unresolved emotional issues can harm unborn children, referring to a study that showed that "women were 60 per cent more likely to survive breast cancer if they had a fighting spirit than if they felt helpless and hopeless", and the recommendation that the recently bereaved should use Ainsworth Rescue Remedy and Flower Essences "if you find you are really sinking".

And by the time you get to the end of the chapter on food, even the most robustly independent psyche will be shaken. Not content with putting a justified boot into junk food, Caplin makes you wonder how we ever survived the dangers of red meat, eggs, nuts, bread, fruit, milk and the careless combinations in which we have been eating them for these past few hundred millennia. Orange and grapefruit acidity draws calcium from the bones and teeth, alkaloids from "stressful" vegetables like aubergine and potatoes block vitamin B absorption ... the list is exhaustive and exhausting.

This is the defining feature of any self-help book, of course - to enfeeble as it purports to empower. This is why it's worth getting worked up about a book like Lifesmart . Alone, it wouldn't matter - one book and a few fools being parted from their money harms no one - but it's part of a multimillion-pound industry that indulges narcissism and navel-gazing, erodes trust in doctors, and renders the emotionally continent and self-possessed instantly suspicious. It may clear your colon but it's crippling the national cortex.

After Caplin, the brisk pedagogic tone of Mireille Guiliano's French Women Don't Get Fat comes at first as a welcome relief. First Guiliano (president and CEO of Clicquot, Inc in New York and director of Champagne Veuve Clicquot in Reims) tells the cautionary tale of her youth: French teenager goes to America, eats like an American, gains a stone in a year, returns home to family that starts bleeding from the eyes when it beholds the fat-slabbed body of its formerly svelte member until "Dr Miracle" turns up and vouchsafes her the sacred knowledge that " tout est question d'équilibre." Under his tutelage she learns that if one doesn't stuff one's face with patisserie until one starts to leak marzipan from les oreilles, one will be able to enjoy a little bit of everything, from bread to wine to chocolate.

The rest of the book sets out this basic truth at gruelling length and is made more wearisome by its constant attribution of various commonplace skills to innate Gallic talent and wisdom - French women can vary dishes just as they have "an uncanny knack for using the same scarf to create a different effect"; they know how to keep meals interesting just as "in love we blend versatility with constancy, the stiff and the supple, the excitement of glamour with the pleasure of comfort", and so on.

By their very nature, diet books have to be slightly didactic, but - as you may have noticed in the preceding paragraph - Guiliano frequently slips into a patronising tone that is aggravated by her blissful ignorance of how the vast majority of people (who aren't champagne-swilling CEOs and didn't grow up surrounded by gardens full of fruit trees and bushes to put them in touch with the seasons) live and that serves only to irritate and alienate the reader - especially, I'd have thought, the American market at which the treatise is clearly aimed. I liked best Guiliano's suggestion that for extra exercise one could iron one's own clothes. She's much better when simply rhapsodising about the pleasures of good food - it is perhaps as a figurehead for the growing slow food movement that she will find her true metier.

Nigel Denby's The GL Diet is more straightforward. It aims to eliminate anomalies thrown up by the GI diet (currently filling the vacuum left by Atkins's fall from grace) - like both bread and carrots being high on the glycaemic index but the latter being obviously the better thing to eat. Denby has come up with an equation that controls portion sizes, which renders carrots once again safe for dieting democracy. The rest is the traditional blend of case studies, recipes, affirmations, and a postscript about the need to eat a variety of fruit and veg, keep hydrated, avoid certain fats, take exercise and reduce salt that makes me think of the story of the woman who made stone soup. The stone was the much publicised main ingredient, so the indispensable covert additions that made the soup effective went unnoticed by her guests.

Perhaps the last word should go to a friend who lost three stone last year. When asked how she did it, she replied: "I stopped pushing things down my fat frigging throat." Such succinct wisdom - and she's not even French.