Why We Get Fat: And What to Do About It (7 page)

Considering the ubiquity of the message, the hold it has on our lives, and the elegant simplicity of the notion—burn calories, lose weight, prevent disease—wouldn’t it be nice if it were true? As a culture, we certainly believe it is. Faith in the health benefit of physical activity is now so deeply ingrained in our consciousness that it’s often considered the one fact in the controversial science of health and lifestyle that must never be questioned.

There are indeed excellent reasons to exercise regularly. We can increase our endurance and fitness by doing so; we may live longer, perhaps, as the experts suggest, by reducing our risk of heart disease or diabetes. (Although this has yet to be rigorously tested.) We may simply feel better about ourselves, and it’s quite clear that many of us who do exercise regularly, as I do, become exceedingly fond of the activity. But the question I want to explore here is not whether exercise is fun or good for us (whatever that ultimately means) or a necessary adjunct of a healthy lifestyle, as the authorities are constantly telling us, but whether it will help us maintain our weight if we’re lean, or lose weight if we’re not.

The answer appears to be no.

Let’s look at the evidence. I want to begin with the observation I made in
chapter 1
that obesity associates with poverty. In the United States, Europe, and other developed nations, the poorer people are, the fatter they’re likely to be. It’s also true that the poorer we are, the more likely we are to work at physically demanding occupations, to earn our living with our bodies rather than our brains.

It’s the poor and disadvantaged who do the grunt work of
developed nations, who sweat out a living not just figuratively but literally. They may not belong to health clubs or spend their leisure time (should they have any) training for their next marathon, but they’re far more likely than those more affluent to work in the fields and in factories, as domestics and gardeners, in the mines and on construction sites. That the poorer we are the fatter we’re likely to be is one very good reason to doubt the assertion that the amount of energy we expend on a day-to-day basis has any relation to whether we get fat. If factory workers can be obese, as I discussed earlier, and oil-field laborers, it’s hard to imagine that the day-to-day expenditure of energy makes much of a difference.

Another very good reason to doubt that assertion is, once again, the obesity epidemic itself. We’ve been getting steadily fatter for the past few decades, and this might suggest, as many authorities do—the World Health Organization among them—that we’ve been getting more sedentary. But the evidence suggests the opposite, certainly in the United States, where the obesity epidemic has coincided with what we might call an epidemic of leisure-time physical activity, of health clubs and innovative means of expending energy (in-line skating, mountain biking, step and elliptical machines, spinning and aerobics, Brazilian martial-arts classes—the list goes on), virtually all of which were either invented or radically redesigned since the obesity epidemic began.
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Until the 1970s, Americans were not believers in the need to spend leisure hours sweating, not if they could avoid it. In the mid-1970s, as was pointed out by William Bennett and Joel Gurin in their 1982 book on obesity,
The Dieter’s Dilemma
, it “still
seemed a little strange to see people go running down a city street in the colorful equivalent of underwear.” But this is no longer the case. Indeed,
The New York Times
reported in 1977 that the United States was
then
in the midst of an “exercise explosion,” and this was only happening because the widespread belief of the 1960s that exercise was “bad for you” had been transformed into the “new conventional wisdom—that strenuous exercise is good for you.” In 1980,
The Washington Post
reported that one hundred million Americans had become active members of the “new fitness revolution” and that many of these “would have been derided as ‘health nuts’ ” just a decade earlier. “What we are seeing,” the
Post
reported, “is one of the late twentieth century’s major sociological events.”

But if sedentary behavior makes us fat and physical activity prevents it, shouldn’t the “exercise explosion” and the “new fitness revolution” have launched an epidemic of leanness rather than coinciding with an epidemic of obesity?

As it turns out, very little evidence exists to support the belief that the number of calories we expend has any effect on how fat we are. In August 2007, the American Heart Association (AHA) and the American College of Sports Medicine (ACSM) addressed this evidence in a particularly damning manner when they published joint guidelines on physical activity and health. The ten expert authors included many of the preeminent proponents of the essential role of exercise in a healthy lifestyle. Put simply, these were people who really want us to exercise and might be tempted to stack the evidence in favor of our doing so. Thirty minutes of
moderately vigorous physical activity, they said, five days a week, was necessary to “maintain and promote health.”

But when it came to the question of how exercising affects our getting fat or staying lean, these experts could only say: “It is reasonable to assume that persons with relatively high daily energy expenditures would be less likely to gain weight over time, compared with those who have low energy expenditures. So far, data to support this hypothesis are not particularly compelling.”

The AHA/ACSM guidelines were a departure from the recent guidelines of other authoritative agencies—the U.S. Department of Agriculture (USDA), the International Association for the Study of Obesity, and the International Obesity Taskforce—all of which recommended that we should exercise an hour a day. But the reason these other authorities advocate more exercise is not to help us lose fat, which they tacitly acknowledge cannot be done by exercising alone; rather, it’s to help us avoid getting fatter.

The logic behind the one-hour recommendations is based precisely on the paucity of evidence to support the notion that exercising any less has any effect. Since few studies exist to tell us what happens when people exercise for more than sixty minutes each day, these authorities can imagine that this much exercise
might
make a difference. The USDA guidelines have suggested that up to ninety minutes a day of moderately vigorous exercise—an hour and a half every day!—may be necessary just to
maintain
weight loss, but they have not suggested that weight can be lost by exercising more than ninety minutes.

The evidence leaves little room for argument. To call it “not particularly compelling,” as the American Heart Association and the American College of Sports Medicine did, is, well, a little unduly generous. A report that these expert guidelines often defer to as the basis for their assessments was published in 2000 by two Finnish exercise physiologists. These researchers looked at the results of the dozen best-constructed experimental trials that addressed weight maintenance—that is, successful dieters who were trying to keep off the pounds they had shed. They found that
everyone in these studies regained weight. Depending on the type of trial, exercise would either decrease the rate of that gain (by 3.2 ounces per month) or increase its rate (by 1.8 ounces). As the Finns themselves concluded, with characteristic understatement, the relationship between exercise and weight is “more complex” than they might otherwise have imagined.

One study that the Finns could not consider, because it was published in 2006, six years later, is particularly revealing, both in what it concluded and how those conclusions were interpreted. The authors were Paul Williams, a statistics expert at the Lawrence Berkeley National Laboratory in Berkeley, California, and Peter Wood, a Stanford University researcher who has been studying the effect of exercise on health since the 1970s. Williams and Wood collected detailed information on almost thirteen thousand habitual runners (all subscribers to
Runner’s World
magazine) and then compared the weekly mileage of these runners with how much they weighed from year to year. Those who ran the most tended to weigh the least, but
all
these runners tended to get fatter with each passing year, even those who ran more than forty miles a week—eight miles a day, say, five days a week.

This observation led Williams and Wood, both believers in the doctrine of calories-in/calories-out, to suggest that even the most dedicated runners had to increase their distance by a few miles a week, year after year—expend even more energy as they got older—if they wanted to remain lean. If men added two miles to their weekly distance every year, and women three, according to Williams and Wood, then they
might
manage to remain lean, because this might mean expending in running the calories that they seemed fated otherwise to accumulate as fat.

Let’s see where that logic takes us. Imagine a man in his twenties who runs twenty miles a week—say, four miles a day, five days a week. According to Williams and Wood (and the logic and mathematics of calories-in/calories-out), he will have to double that in his thirties (eight miles a day, five days a week) and triple it
in his forties (twelve miles a day, five days a week) to keep fat from accumulating. A woman in her twenties who runs three miles a day, five times a week—an impressive but not excessive amount—would have to up her daily distance to fifteen miles in her forties to retain her youthful figure. If she does eight-minute miles, a nice pace for such a distance, she’d better be prepared to spend two hours on each of her running days to keep her weight in check.

If we believe in calories-in/calories-out, and that in turn leads us to conclude that we have to run half-marathons five days a week (in our forties, and more in our fifties, and more in our sixties …) to maintain our weight, it may, once again, be time to question our underlying beliefs. Maybe it’s something other than the calories we consume and expend that determines whether we get fat.

The ubiquitous faith in the belief that the more calories we expend, the less we’ll weigh is based ultimately on one observation and one assumption. The observation is that people who are lean tend to be more physically active than those of us who aren’t. This is undisputed. Marathon runners as a rule are not overweight or obese; the front-runners in marathons often look emaciated.

But this observation tells us nothing about whether runners would be fatter if they didn’t run or if the pursuit of distance running as a full-time hobby will turn a fat man or woman into a lean marathoner.

We base our belief in the fat-burning properties of exercise on the assumption that we can increase our energy expenditure (calories-out) without being compelled to increase our energy intake (calories-in). Burn 150 extra calories every day in exercise and keep it up for a month, as
New York Times
reporter Gina Kolata calculated in her 2004 book,
Ultimate Fitness
, and you could lose a pound “if you do not change your diet.”

The key question, though, is whether this is a reasonable possibility.
Is it true that we can increase our expenditure of calories, burn an extra 150 calories a day, say, or go from being sedentary to active or from active to very active, without changing our diet—without eating more—and without maybe decreasing the amount of energy we expend in the hours between our bouts of exercise?

The simple answer, again, is no. I’ve already introduced the concept that explains why, one that used to seem perfectly obvious but has now been relegated to the dustbin of exercise and nutrition history. This is the idea that if we increase our physical activity we will “work up an appetite.” If you go for a walk or rake some leaves, take a long hike, play two sets of tennis or eighteen holes of golf, you work up an appetite. You get hungry or hungrier. Increase the energy you expend and the evidence is very good that you will increase the calories you consume to compensate.

That we have gotten to the place in our lives, and in the science of exercise, nutrition, and weight, where this concept of working up an appetite, of the body’s increasing its intake of energy to compensate for its increased expenditure, has been forgotten is one of the stranger stories in the history of modern medical research, or at least I hope it is.

Until the 1960s, most clinicians who treated obese patients dismissed as naïve the notion that we could lose weight through exercise or gain it by being sedentary. When Russell Wilder, an obesity and diabetes specialist at the Mayo Clinic, lectured on obesity in 1932, he said his fat patients lost more weight with bed rest, “while unusually strenuous physical exercise slows the rate of loss.” “The patient reasons quite correctly,” Wilder said, “that the more exercise he takes the more fat should be burned and that loss of weight should be in proportion and he is discouraged to find that the scales reveal no progress.”

The patient’s reasoning had two flaws, as Wilder’s contemporaries would point out. First, we burn surprisingly few calories
doing moderate exercise, and, second, the effort can be easily undone, and probably will be, by mindless changes in diet. A 250-pound man will burn
three
extra calories climbing one flight of stairs, as Louis Newburgh of the University of Michigan calculated in 1942. “He will have to climb twenty flights of stairs to rid himself of the energy contained in one slice of bread!”

So why not skip the stairs and skip the bread and call it a day? After all, what are the chances that if a 250-pounder does climb twenty extra flights a day he won’t eat the equivalent of an extra slice of bread before the day is done?

Yes, more strenuous exercise will burn more calories—“it really is much more effective to exercise hard enough to sweat,” Kolata tells us, “and that is the only way to burn large numbers of calories”—but, as these physicians argued, it will also make you hungrier still.

“Vigorous muscle exercise usually results in immediate demand for a large meal,” noted Hugo Rony of Northwestern University in 1940. “Consistently high or low energy expenditures result in consistently high or low levels of appetite. Thus men doing heavy physical work spontaneously eat more than men engaged in sedentary occupations. Statistics show that the average daily caloric intake of lumberjacks is more than 5,000 calories while that of tailors is only about 2,500 calories. Persons who change their occupation from light to heavy work or
vice versa
soon develop corresponding changes in their appetite.” So, if a tailor becomes a lumberjack and, by doing so, takes to eating like one, why assume the same thing wouldn’t happen, albeit to a lesser extent, to an overweight tailor who chooses to work out like a lumberjack for an hour a day?
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