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When it comes to eating and weight loss, the brain has a mind of its own. It is powerful, it is intelligent and, whether we like it or not, it is in control.Photo illustration: The Globe and Mail. Source images: iStock.

Mark Schatzker’s latest book, The End of Craving: Recovering the Lost Wisdom of Eating Well, was published this week.

In 1977, the American government released Dietary Goals for the United States, a document that urged the country to “increase carbohydrate consumption” and cut down on butterfat, eggs and red meat. The now infamous “war on fat” had begun. Butter gave way to margarine. Kids drank two per cent instead of homo milk. And meatloaf with mashed potatoes was replaced by skinless chicken breast with steamed vegetables.

It didn’t work. All that supposedly healthy, low-fat eating didn’t reduce obesity – it pushed the U.S. national rate up by 15 points. So, after two decades of fruitless lean eating, we unleashed our frustration on what we were told was, in fact, the true nutritional villain: carbs. For another 20 years, we basked in one newfound style of carbohydrate restriction after another: the Zone, Atkins, paleo, keto.

And once again, it didn’t work. Since 1985, the rate of obesity in Canada has tripled. South of the border, 42 per cent of adults now have obesity.

What did we get wrong?

We thought that weight gain came down to eating the wrong nutrient – first it was fat, then carbs – and that the key to weight loss was to simply eat less of that nutrient. The first part of that assumption, we now know, is wrong. Eating fat can make you fat, and so can eating carbs. People with obesity tend to eat too much of both.

But that’s not all we got wrong. The second half of that assumption – that people can eat less food if they choose to – is also wrong.

During the war on fat, Americans overdid it on the carbs, as we now know. But fat intake didn’t even go down – it held even. Thanks to the success and popularity of the low-carb movement, Canadians reduced both bread and sugar intake, only to find that obesity went up, not down. The more we try to eat less, the harder it seems to become.

To the scientists who study obesity, this is anything but a surprise.

In 1959, a physician named Jules Hirsch discovered first-hand the stubborn nature of body weight. Four of his patients, who collectively weighed 1,290 pounds, lived at Rockefeller University Hospital for eight months where they subsisted on a liquid diet that delivered a fraction of their caloric requirement. Each patient lost an average of 100 pounds, and the day they were discharged, everyone, including Dr. Hirsch, welcomed the new, thinner, happier life that awaited them. But they quickly gained it all back.

In 2009, Kevin Hall, the Canadian-born physiologist who studies metabolism at the National Institutes of Health in Bethesda, Md., began studying the contestants competing on The Biggest Loser. After 30 weeks of vigorous exercise and diet, the weight of the average contestant dropped from 328 to 202 pounds. Their bodies weren’t just slimmer, however. They ran differently. Their “resting metabolic rate,” which refers to the energy required just to stay running – to breathe, pump blood, blink and yawn – had slowed down. Some of this was expected, because it takes less energy to run a smaller body, the same way it takes less gas to power a smaller car. But the drop was too big. On average, each contestant was using 275 fewer calories per day than expected – about half a Big Mac’s worth – just to function. They were running in super-economy mode.

Six years later, Dr. Hall performed a follow-up study on 14 of the original 16 contestants. All but one had gained weight. Three had bounced back to their initial weight, one was 29 pounds heavier and one was a full 54 pounds heavier than the day the contest began. It sounds like a classic failure of willpower. But that’s not what happened at all. The contestants were still exercising. They were still eating less. On average, each was now consuming 375 fewer calories a day than when the competition had started. They were experiencing “persistent metabolic adaptation.” Their metabolisms were stuck in economy mode.

By all rights, they should have been skinnier. And the reason wasn’t because of fat or carbs. It was because of their brains.

The human brain regulates bodyweight. Let me say it again: The human brain regulates bodyweight. Just as your brain controls body temperature, heart rate or how much you sweat, it exerts a similar control on how much you weigh.

The very fact that we keep bouncing from diet to diet is evidence of this existential condition. All diets work in the beginning. The pounds melt away. Pants that were formerly too tight fit once again. But the weight comes back, usually starting around the six-month mark. The exasperated dieter swears he is eating less, but the scale claims otherwise. Fatigue sets in and we are beset by food cravings. Why? Because the brain is resisting weight loss. It wants you to eat.

The brain isn’t just opposed to losing weight. It opposes gaining weight, too. In “overfeeding studies,” human subjects – even obese subjects – find that eating too much renders the mere thought of food extremely unpleasant. In some experiments, overfed subjects have even shown a tendency to increase their metabolic rate to burn the extra calories they are consuming. And when these studies mercifully come to an end, the subjects lose their added weight.

If this all seems too hard to believe, consider the Masa people of northern Cameroon and Chad, who consider fatness to be a sign of wealth and virility among young men. Every year, a small number embark on a period of incredible food intake called the guru walla. The aim is to achieve a bulging stomach, large buttocks and a smooth layer of buttery fat spread over their entire frame. To achieve this, they live in a hut by themselves, often naked, for two months, eating every two hours, give or take, from six in the morning until four the next morning.

In 1976, a guru walla participant ate more than 17 pounds of food in a single day, totalling 16,823 calories – the caloric equivalent of a wheelbarrow filled with 30 Big Macs. By the end of his guru walla, he’d gained 64 pounds. A fellow participant who gained 75 pounds couldn’t get up without using a stick for help.

“The feeding hours,” two French anthropologists described, “are punctuated by a good deal of vomiting, farting, defecating and urinating.” It is a battle. The Masa men have to sit upright, with their heads held just so to keep themselves from vomiting out the food they’ve worked so hard to get down.

Here, alas, is the starkest irony of them all. Like the hundreds of millions of frustrated, depressed dieters on the other side of the planet – the millions who lose weight only to find it comes back – the Masa cannot maintain their ideal, hard-won weight. Over the months that follow, that fabulous buttery sheen disappears, and they are soon back where they started. They want to be fat. But they are doomed to be thin.

When it comes to eating, the brain has a mind of its own. It is powerful, it is intelligent and, whether we like it or not, it is in control. And only by understanding that hidden aspect of ourselves can we hope to at last eat well and be well.

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