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Obesity isn’t new, but the obesity epidemic is. We went from a few corpulent kings and queens, like Henry VIII or Louis VI (known as Louis le Gros, or “Louis the Fat”), to a pandemic of obesity, now considered to be perhaps the most dire and poorly-contained public health threat of our time. About 37 percent of American men are obese, and 41 percent of American women, with no end in sight. Earlier reports had suggested at least the rise in obesity was slowing down, but even that doesn’t appear to be the case. Similarly, we had thought we were turning the corner on childhood obesity after 35 years of unrelenting bad news; but, the bad news continues. Child and adolescent obesity rates have continued to rise, now into the fourth decade.

Over the last century, obesity appears to have jumped tenfold, from about 1 in 30 to now 1 in 3. But it wasn’t a steady rise. Something seems to have happened around the late 1970s, and not just here, but around the globe. The obesity pandemic took off at about the same time across the world in most high-income countries in the 1970s and 1980s. The fact that the rapid rise appeared almost concurrently across the industrialized world suggests a common cause. What might that trigger have been?

Any potential driver would have to be global in nature, and coincide with the upswing of the epidemic. So, the change would have had to have started about 40 years ago, and would have been able to spread rapidly around the globe. Let’s see how all the various theories stack up. For example, some have blamed changes in our “built environment”––shifts in city planning that have made our communities less conducive to walking, biking, and grocery shopping. But that doesn’t meet our criteria for a credible cause, because there was no universal, simultaneous change in our neighborhoods within that time frame.

If you do a survey of hundreds of policymakers, most blame the obesity epidemic on “lack of personal motivation.” But do you see how little sense that makes? Here in the U.S, for example, obesity shot up across the entire population in the late 1970s. Are you telling me that every single sector of the entire population suffered some sort of simultaneous decline in willpower? Each age, sex, and ethnic group, with all their different attitudes and experiences, coincidentally lost their collective capacity for self-control at the same time? More plausible than a global change in the nature of our characters would be some global change in the nature of our lives.

The food industry blames inactivity. “If all consumers exercised,” said the CEO of PepsiCo, “obesity wouldn’t exist.” Coca-Cola went a step further, spending $1.5 million to create the Global Energy Balance Network to downplay the role of diet. Leaked emails show the company planned on using the front to serve as a “weapon” to “change the conversation” about obesity in its “war” with the public health community.

This tactic is so common among food and beverage companies it even has a name: “leanwashing.” You’ve heard of greenwashing, where companies deceptively pretend to be environmentally friendly. Leanwashing is the term used to describe companies that try to position themselves as helping to solve the obesity crisis when they’re instead directly contributing to it. Indeed, the largest food company in the world, for example—Nestlé—has rebranded itself as the “world’s leading nutrition, health and wellness company.” Yes, that Nestlé, makers of Cookie Crisp and historically more than 100 different brands of candy, including Butterfinger, Kit Kat, Goobers, Gobstoppers, Runts, and Nerds. Another of their slogans is “Good Food, Good Life.” Their Raisinets may have some fruit, but they seem to me more Willy Wonka than wellness. Let’s just say that on their “What is Nestlé doing about obesity?” webpage, their “Read about our Nestlé Healthy Kids programme” link gives you a Page Not Found error.

The constant corporate drumbeat of overemphasis on physical inactivity appears to be working. In response to a Harris poll question, “Which of these do you think are the major reasons why obesity has increased?”, a large majority chose lack of exercise, while only 34 percent chose excess calorie consumption. That’s actually been identified as one of the most common misconceptions about obesity. The scientific community has come to a fairly decisive conclusion that the factors governing calorie intake more powerfully affect overall calorie balance. It’s more our fast food than our slow motion.

There’s even considerable debate in the scientific literature as to whether changes in physical activity have had “any role whatsoever” in the obesity epidemic. The increase in caloric intake per person is more than enough to explain the obesity epidemic in the United States and around the rest of the world. In fact, if anything, the level of physical activity over the last few decades has actually slightly gone up in both Europe and North America. Ironically, this may actually be a result of the extra energy it takes to move around our heavier bodies, making it a consequence of the obesity problem, rather than the cause.

Formal exercise is only a small part of our total daily activity, though. Think about how much more physical work people used to do in the workplace, or on the farm, or even in the home. It’s not just the shift in collar color from blue to white. Increasing automation, computerization, mechanization, motorization, and urbanization have all contributed to increasingly more sedentary lifestyles over the last century. But that’s the problem with the theory. The occupational shifts and advent of labor-saving devices has been gradual, and largely predated the dramatic recent rise in weight gain the world over. Washing machines, vacuum cleaners, and the Model T were all invented before 1910. Indeed, when put to the test using state-of-the-art methods to measure energy in and energy out, it was caloric intake, not physical activity, that predicted weight gain over time.

The common misconception that obesity is mostly due to lack of exercise may not just be a benign fallacy. Personal theories of causation appear to impact people’s weight. Those who blame insufficient exercise are significantly more likely to be overweight. Put them in a room with chocolate, and they can be covertly observed consuming more candy.

Those holding that view may be different in other ways, though. You can’t prove cause-and-effect until you put it to the test. And indeed, people randomized to read an article implicating inactivity went on to eat significantly more sweets than those reading about research that indicted diet. A similar study evidently found that those presented with research blaming genetics subsequently ate significantly more cookies. The paper was entitled “An unintended way in which the fat gene might make you fat.”

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