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We should now know enough about our ingestive instincts to treat them with extreme caution. In the 1990, scientists discovered why eating is such a compelling pleasure: when we scoff something sweet or fatty, the brain rewards itself with heroin-like chemicals called endogenous opioids. This means that snacks such as sweet biscuits act on the same pleasure centres that respond to addictive drugs. More recent studies show that the mere thought of yummy ice cream can set off the same pleasure centres in healthy people as photos of crack pipes do for freebasing addicts. We also get a druggy kick from physically stuffing our stomachs, according to an experiment that electronically stimulated the vagus nerves in overweight people. The vagus is a phone-line from our bellies to our heads that tells the primitive lower brain when our guts are brim-full. When it was artificially activated, junkie- type highs were seen in the volunteers’ minds. 

So we like food. A lot. And our brains don’t let us forget thanks again to our ancestors. The secret of hunter-gathering is being able to find all the edibles faster than the next guy. The best practitioners survived to pass on their genes, so we have inherited gastrophile minds that constantly ruminate about where we’ve eaten, what we’ve eaten, how it tasted and how we might get it again. Then our reward centres badger us to repeat the experience. All this makes it extremely hard for many of us to diet. Studies show that it takes four months of complete abstinence for us to start losing our cravings for forbidden fattening foods. There’s also a physical obstacle to weight-loss: once we’ve put on fat, the podge tends to stay put because our bodies have learnt to act like calorie-hoarding hamster cheeks. The human frame contains around ten times more fat- storing cells in relation to its body mass than most animals (polar bears are similarly fat-rich). Our famine-resistant frames have strong mechanisms to stop weight loss, but weak systems for preventing weight gain. If you manage to lose 10 percent of your weight, your body starts to think there’s an emergency. So it burns less fuel by slowing your metabolism and dropping your temperature. This plateau effect kicks in after around eight weeks of dieting, So the weight-loss stops, morale slumps, and the cravings remain.

Dieting also makes our metabolisms rebound badly. An analysis of 31 long-term clinical studies found that diets don’t work in the long run. Within five years about two- thirds of dieters put back the weight they lost – and more. It concluded that most of them would have been better off not dieting at all. Their weight would be pretty much the same and their bodies would not have suffered wear and tear from yo-yoing. This backfire effect is worst among teenagers: people who start habitually dieting young tend to be significantly heavier after five years than teens who never dieted. The young starvers tend to skip breakfast, then binge-eat later in the day, just as their primitive brains would prime them to do. Thus they set the pattern for a lifetime. All these physical responses are a fantastic survival strategy for the Pleistocene age, but a cruel trick in the twenty-first century.

Excerpted from pages 58 to 60 of Enough: breaking free from the world of excess by John Naish