Elizabeth Kolbert calls it a mystery batter-dipped in an enigma:
According to the first National Health study, which was done in the early nineteen-sixties, 24.3 per cent of American adults were overweight — roughly defined as having a body-mass index greater than twenty-seven. (The metrics are slightly different for men and women; by the study’s definition, a woman who is five feet tall would count as overweight if she was more than a hundred and forty pounds, and a man who is six feet tall if he weighed more than two hundred and four pounds.)
By the time of the second survey, conducted in the early nineteen-seventies, the proportion of overweight adults had increased by three-quarters of a per cent, to twenty-five per cent, and, by the third survey, in the late seventies, it had edged up to 25.4 per cent. The results that Flegal found so surprising came from the fourth survey. During the nineteen-eighties, the American gut, instead of expanding very gradually, had ballooned: 33.3 per cent of adults now qualified as overweight.
Flegal began asking around at professional meetings. Had other researchers noticed a change in Americans’ waistlines? They had not. This left her feeling even more perplexed. She knew that errors could have sneaked into the data in a variety of ways, so she and her colleagues checked and rechecked the figures. There was no problem that they could identify. Finally, in 1994, they published their findings in the Journal of the American Medical Association. In just ten years, they showed, Americans had collectively gained more than a billion pounds. “If this was about tuberculosis, it would be called an epidemic,” another researcher wrote in an editorial accompanying the report.
During the next decade, Americans kept right on gaining. Men are now on average seventeen pounds heavier than they were in the late seventies, and for women that figure is even higher: nineteen pounds. The proportion of overweight children, age six to eleven, has more than doubled, while the proportion of overweight adolescents, age twelve to nineteen, has more than tripled.
(According to the standards of the United States military, forty per cent of young women and twenty-five per cent of young men weigh too much to enlist.)
One explanation is known as the mismatch paradigm:
“We evolved on the savannahs of Africa,” Power and Schulkin write. “We now live in Candyland.”
But that doesn’t explain the recent increase in weight — which might be an economic phenomenon:
Between 1983 and 2005, the real cost of fats and oils declined by sixteen per cent. During the same period, the real cost of soft drinks dropped by more than twenty per cent.
“For most people, an ice cold Coca-Cola used to be a treat reserved for special occasions,” Finkelstein observes. Today, soft drinks account for about seven per cent of all the calories ingested in the United States, making them “the number one food consumed in the American diet.” If, instead of sweetened beverages, the average American drank water, Finkelstein calculates, he or she would weigh fifteen pounds less.
Much of the issue revolves around portion sizes:
n the early nineteen-sixties, a mannamed David Wallerstein was running a chain of movie theatres in the Midwest and wondering how to boost popcorn sales. Wallerstein had already tried matinée pricing and two-for-one specials, but to no avail. According to Greg Critser, the author of “Fat Land (2003), one night the answer came to him: jumbo-sized boxes. Once Wallerstein introduced the bigger boxes, popcorn sales at his theatres soared, and so did those of another high-margin item, soda.
A decade later, Wallerstein had retired from the movie business and was serving on McDonald’s board of directors when the chain confronted a similar problem. Customers were purchasing a burger and perhaps a soft drink or a bag of fries, and then leaving. How could they be persuaded to buy more? Wallerstein’s suggestion — a bigger bag of fries — was greeted skeptically by the company’s founder, Ray Kroc. Kroc pointed out that if people wanted more fries they could always order a second bag.
“But Ray,” Wallerstein is reputed to have said, “they don’t want to eat two bags — they don’t want to look like a glutton.” Eventually, Kroc let himself be convinced; the rest, as they say, is supersizing.
The elasticity of the human appetite is the subject of Brian Wansink’s Mindless Eating (2006). Wansink is the director of Cornell University’s Food and Brand Lab, and he has performed all sorts of experiments to test how much people will eat under varying circumstances. These have convinced him that people are — to put it politely — rather dim. They have no idea how much they want to eat or, once they have eaten, how much they’ve consumed. Instead, they rely on external cues, like portion size, to tell them when to stop. The result is that as French-fry bags get bigger, so, too, do French-fry eaters.
Consider the movie-matinée experiment. Some years ago, Wansink and his graduate students handed out buckets of popcorn to Saturday-afternoon filmgoers in Chicago. The popcorn had been prepared almost a week earlier, and then allowed to become hopelessly, squeakily stale. Some patrons got medium-sized buckets of stale popcorn and some got large ones. (A few, forgetting that the snack had been free, demanded their money back.) After the film, Wansink weighed the remaining kernels. He found that people who’d been given bigger buckets had eaten, on average, fifty-three per cent more.
In another experiment, Wansink invited participants to cook dinner for themselves with ingredients that he provided. One group got big boxes of pasta and big bottles of sauce, a second smaller boxes and smaller bottles. The first group prepared twenty-three per cent more, and downed it all. In yet another experiment, Wansink rigged up bowls that could be refilled, via a hidden tube. When he served soup out of the trick bowls, people, he writes, “ate and ate and ate.” On average, they consumed seventy-three per cent more than those who were served from regular bowls. “Give them a lot and they eat a lot,” he writes.
Before McDonald’s discovered the power of re-portioning, it offered just a small bag of French fries, which contained two hundred calories. Today, a small order of fries has two hundred and thirty calories, and a large order five hundred. (Add fifteen calories for each package of ketchup.) Similarly, a McDonald’s soda used to be eight ounces. Today, a small soda is sixteen ounces (a hundred and fifty calories), and a large soda is thirty-two ounces (three hundred calories).
Perhaps owing to the influence of fast-food culture, up-sizing has by now spread to all sorts of other venues. In a 2002 study, Marion Nestle, a nutrition professor at New York University, and Lisa Young, an adjunct there, examined the offerings, past and present, at American supermarkets. They found that during the nineteen-eighties the amount of food that was counted as a single serving increased rapidly.
A similar jump showed up in cookbooks; when the researchers compared dessert recipes in old and new editions of volumes like The Joy of Cooking, they discovered that, even in cases where the recipes themselves had remained unchanged, the predicted number of servings had shrunk.
According to the federally supported National Heart, Lung, and Blood Institute, the bagels that Americans eat have in the past twenty years swelled from a hundred and forty to three hundred and fifty calories each. If, as Wansink argues, people are relying on external cues to determine their consumption, then the new, bigger bagel is sneaking in an additional two hundred and ten calories. For someone who is in the habit of eating a bagel a day, these extra calories translate into a weight gain of more than a pound a month.
This year marks the 80th that 
When he brought on a savvy marketer, Charles Roman, who coined the dynamic-tension name, the money started rolling in. It didn’t last forever — but it has come back:
Your dentist probably never told you that 
