Take a stroll into any bookshop and you won’t suspect a thing: the shelves are heaving with summer-diet tomes, from Crash Diet — Lose 7lbs in 7 Days to Bikini Bootcamp: Two Weeks to Your Ultimate Beach Body and, perhaps most optimistic of all, The Revenge Diet: Make Him Sorry He Dumped You! Lose 15lbs in a Month. Yet, despite appearances, the diet industry is in the throes of a backlash. It started with The Diet Delusion and Rethinking Thin, both of which challenged conventional wisdom about weight loss. Now comes something even more revolutionary, the splendidly titled Dieting Makes You Fat. Its author, Geoffrey Cannon, is unequivocal in his belief that dieting causes the very condition it is meant to cure.

His argument is simple: in evolutionary terms, the human body cannot distinguish between dieting and famine. We are hard-wired to respond to the threat of an insecure food supply by retaining body fat rather than burning it off, just as camels are biologically designed to store fat in humps to survive forays in the desert. “The more we endure cycles of dieting, the more our bodies become trained to seek out food, slow down vital functions and conserve body fat,” he says. Apparently, it’s evolution, not lack of willpower, that causes us to seek out sweet foods. “In the forest, sweetness was nature’s way of telling early humans that fruit was safe to eat.”

For anyone who has ever tried to stick to a diet, some of Cannon’s advice might come as a shock. He says that restricting calories is the worst possible way to achieve the body of your dreams. “If you have more body fat than you want, don’t even think of going on a diet,” he warns. “Be more physically active instead, and be patient. You need to train your body to build up lean tissue, which works more efficiently than body fat.” He isn’t advocating that you go and binge on Krispy Kremes, but suggests that if you are active, then you can enjoy a balance of good food — even cake.

Cannon points out that there are huge misconceptions about the link between physical activity and weight loss. “Many people, including GPs, mistakenly believe that the amount of exercise you need to take is huge, and they’re still thinking in terms of energy balance — for example, playing two hours of squash to work off a cupcake.” Researchers at Stanford University, however, found that people who exercised regularly burnt off 500-700 more calories a day than their sedentary counterparts. Crucially, fit bodies burnt off this energy largely during the time they were resting, not just while they were pounding away on the treadmill.

Somewhat unusually for a writer in this field, Cannon has direct experience of the misery of being overweight. He battled through a childhood fuelled by comfort eating following his parents’ divorce — fish and chips with pickled cucumbers, washed down with Tizer — and he continued to struggle through his years at Oxford, where he discovered the delights of cucumber sandwiches layered with butter and salt. He writes movingly about how his emotional hunger for a true home led him to overeat through marriage break-ups and career changes, including a stint at The Sunday Times, before he became a nutrition writer and campaigner. Eventually, it was running, not dieting, that got him on the path to thin.

Nor is Cannon jumping on the anti-diet bandwagon: Dieting Makes You Fat was originally a bestseller in 1983. He decided to write a 21st-century version of the book to tackle issues such as the global obesity time bomb and phenomena such as Atkins, about which he is dismissive. “It’s quite tricky to know what he was going on about,” he says. “In as much as I understand, if you’re on 1,500 calories a day, and are not encouraged to take any physical activity, then it’s not going to work. I don’t care how many people say it does.” Fortuitously, research published by UCLA last year, while Cannon was working on the new edition, concluded that — guess what? — diets don’t work.

The lead author of the study, Traci Mann, noted: “You can initially lose 5%-10% of your weight on any number of diets, but then the weight comes back. We found that the majority of people regained all the weight, plus more.” The success rate for maintaining weight loss five years after a diet ends is estimated at only 5%.

“People make the mistake of judging the success of a diet at the point that it is stopped,” says Cannon, who points out that this is like assessing the state of your finances based on the one day in the month when your account is in the black. “It’s madness. Dieting triggers the body to go into reversal. When people come off a regime, it’s a form of the bulimic syndrome. They find they can’t stop eating. I’ve had that when coming off a diet, and it’s scary.”

Is this really true of every diet, even a teensy crash diet in the week before you hit the beach? Apparently, these are the worst: restricting calorie intake by anything more than 200 calories a day will trigger a rebound effect, and the more drastic and long-lasting the diet, the worse the rebound once it ends. In some studies, people coming off a diet were forced to eat up to 10,000 calories a day — and still reported feeling hungry.

“People often ask me, ‘If this is all true, why haven’t I heard it before?’ Well, my response is, ‘In whose interests is it to tell you?’ The diet industry sells its wares on the basis of repeat custom — if a diet doesn’t work, it’s your fault. It’s time for a paradigm shift. Much of what our bodies do is beyond the control of our minds.”

Cannon accepts that, to most people, the idea that we don’t have control over our appetites is not an attractive one. “That’s why there was such an outcry about Fern Britton’s gastric-band surgery. She knew all along that dieting wasn’t the reason she lost the weight. People don’t want to admit that. I’m sure she is by no means the only high-profile figure to have had one fitted secretly,” he observes, before speculating wildly on other — unprintable — likely candidates.

“Claims made by the diet industry appeal to our base desires, like the e-mail spam messages saying you have won £5m or can enjoy multiple orgasms for ever,” Cannon says. “The dieting business is fabulous. It sells dreams. But dreams rarely come true.”

Dieting Makes You Fat by Geoffrey Cannon (Virgin Books £16.99)

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