How We Grew So Big

By MICHAEL D. LEMONICK

It's hardly news anymore that Americans are just too fat. If the endless parade of articles, TV specials and fad diet books weren't proof enough or you missed the ominous warnings from the National Institutes of Health, the Centers for Disease Control and Prevention and the American Heart Association, a quick look around the mall, the beach or the crowd at any baseball game will leave no room for doubt: our individual weight problems have become a national crisis.

Even so, the actual numbers are shocking. Fully two-thirds of U.S. adults are officially overweight, and about half of those have graduated to full-blown obesity. The rates for African Americans and Latinos are even higher. Among kids between 6 and 19 years old, 15%, or 1 in 6, are overweight, and another 15% are headed that way. Even our pets are pudgy: a depressing 25% of dogs and cats are heavier than they should be.

And things haven't been moving in a promising direction. Just two decades ago, the incidence of overweight in adults was well under 50%, while the rate for kids was only a third what it is today. From 1996 to 2001, 2 million teenagers and young adults joined the ranks of the clinically obese (see "What Is BMI?"). People are clearly worried. A TIME/ABC News poll released this week shows that 58% of Americans would like to lose weight, nearly twice the percentage who felt that way in 1951. But only 27% say they are trying to slim down--and two-thirds of those aren't following any specific plan to do so.

It wouldn't be such a big deal if the problem were simply aesthetic. But excess poundage takes a terrible toll on the human body, significantly increasing the risk of heart disease, high blood pressure, stroke, diabetes, infertility, gall-bladder disease, osteoarthritis and many forms of cancer. The total medical tab for illnesses related to obesity is $117 billion a year--and climbing--according to the Surgeon General, and the Journal of the American Medical Association reported in March that poor diet and physical inactivity could soon overtake tobacco as the leading cause of preventable death in the U.S. And again, Americans recognize the problem. In the TIME/ABC poll they rated obesity alongside heart disease, cancer, AIDS and drug abuse as among the nation's most pressing public health problems.

So why is it happening? The obvious, almost trivial answer is that we eat too much high-calorie food and don't burn it off with enough exercise. If only we could change those habits, the problem would go away. But clearly it isn't that easy. Americans pour scores of billions of dollars every year into weight-loss products and health-club memberships and liposuction and gastric bypass operations--100,000 of the latter last year alone. Food and drug companies spend even more trying to find a magic food or drug that will melt the pounds away. Yet the nation's collective waistline just keeps growing.

It's natural to try to find something to blame--fast-food joints or food manufacturers or even ourselves for having too little willpower. But the ultimate reason for obesity may be rooted deep within our genes. Obedient to the inexorable laws of evolution, the human race adapted over millions of years to living in a world of scarcity, where it paid to eat every good-tasting thing in sight when you could find it.

Although our physiology has stayed pretty much the same for the past 50,000 years or so, we humans have utterly transformed our environment. Over the past century especially, technology has almost completely removed physical exercise from the day-to-day lives of most Americans. At the same time, it has filled supermarket shelves with cheap, mass-produced, good-tasting food that is packed with calories. And finally, technology has allowed advertisers to deliver constant, virtually irresistible messages that say "Eat this now" to everyone old enough to watch TV.

This artificial environment is most pervasive in the U.S. and other industrialized countries, and that's exactly where the fat crisis is most acute. When people move to the U.S. from poorer nations, their collective weight begins to rise. As developing areas like, for example, Southeast Asia and Latin America catch up economically and the inhabitants adopt Western lifestyles, their problems with obesity catch up as well. By contrast, among people who still live in conditions most like those of our distant Stone Age ancestors--such as the Maku or the Yanomami of Brazil--there is virtually no obesity at all.

And that's almost certainly the way it was during 99.9% of human evolution. For most of the 7 million years or so since we parted ways with chimps, life has been very harsh--"nasty, brutish and short," in Thomas Hobbes' memorable phrase. The average life expectancy was probably well under 30. But much of that dismal brevity can be chalked up to accidents, infections, traumatic childbirth and unfortunate encounters with saber-toothed cats and other such predators. If a Cro-Magnon, say, could get past these formidable obstacles, he might conceivably live into his 60s or even longer, with none of the obesity-related illnesses that plague modern Americans.

Our earliest ancestors probably ate much as their cousins the apes did, foraging for fruits, shoots, nuts, tubers and other vegetation in the forests and savannas of Africa. Because most wild plants are relatively low in calories, it took constant work just to stay alive. Fruits, full of natural sugars like fructose and glucose, were an unusually concentrated source of energy, and the instinct to seek out and consume them evolved in many mammals long before humans ever arose. Fruit wasn't always available, but those who ate all they could whenever it was were more likely to survive and pass on their sweet tooth to their progeny.

Our love affair with sugar--and also with salt, another crucial but not always available part of the diet--goes back millions of years. But humanity's appetite for animal fat and protein is probably more recent. It was some 2.5 million years ago that our hominid ancestors developed a taste for meat. The fossil record shows that the human brain became markedly bigger and more complex about the same time. And indeed, according to Katherine Milton, an anthropologist at the University of California, Berkeley, "the incorporation of animal matter into the diet played an absolutely essential role in human evolution."

For starters, meat provided a concentrated source of protein, vitamins, minerals and fatty acids that helped our human ancestors grow taller. The first humans were the size of small chimps, but the bones of a Homo ergaster boy dating back about 1.5 million years suggest that he could have stood more than 6 ft. as an adult. Besides building our bodies, says Emory University's Dr. S. Boyd Eaton, the fatty acids found in animal-based foods would have served as a powerful raw material for the growth of human brains.

Because it's so packed with nutrients, meat gave early humans a respite from constant feeding. Like lions and tigers, they didn't have to eat around the clock just to keep going. But more important, unlike the big cats, which rely mostly on strength and speed to bring down dinner, our ancestors depended on guile, organization and the social and technological skills made possible by their increasingly complex brains. Those who were smartest about hunting--and about gathering the plant foods they ate as part of their omnivorous diets--tended to be better fed and healthier than the competition. They were thus more likely to pass along their genes.

The new appetite for meat didn't mean we lost our passion for sweets, though. As Berkeley's Milton points out, the brain's growth may have been facilitated by abundant animal protein, but the brain operates on glucose, the sugar that serves as the major fuel for cellular function. "The brain drinks glucose 24 hours a day," she says. The sugars in fruit and the carbohydrates in edible grains and tubers are particularly good sources of glucose.

The appetite for meat and sweets were essential to human survival, but they didn't lead to obesity for several reasons. For one thing, the wild game our ancestors ate was high in protein but very low in fat--only about 4%, compared with up to 36% in grain-fed supermarket beef. For another, our ancestors couldn't count on a steady supply of any particular food. Hunters might bring down a deer or a rabbit or nothing at all. Fruit might be in season, or it might not. A chunk of honeycomb might have as many calories as half a dozen Krispy Kreme doughnuts, but you might be able to get it once a year at best--and it wouldn't have the fat.

Beyond that, hunting and gathering took enormous physical work. Chasing wild animals with spears and clubs was a marathon undertaking--and then you had to hack up the catch and lug it miles back to camp. Climbing trees to find nuts and fruit was hard work too. In essence, early humans ate what amounted to the best of the high-protein Atkins diet and the low-fat Ornish diet, and worked out almost nonstop. To get a sense of their endurance, cardiovascular fitness, musculature and body fat, say evolutionary anthropologists, look at a modern marathon runner.

That was the condition of pretty much the entire human race when anatomically modern humans first arose, between 150,000 and 100,000 years ago, and things stayed that way until what some anthropologists have called humanity's worst mistake: the invention of agriculture. We now had a steady source of food, but there were downsides as well. For one thing, our ancestors began gathering in much larger population centers, where bacteria and viruses could fester. Small bands of hunter-gatherers can spread disease only so far, but the birth of cities made epidemics possible for the first time.

Nutritionally, the shift away from wild meat, fruits and vegetables to a diet mostly of cultivated grain robbed humans of many of the essential amino acids, vitamins and minerals they had thrived on. Average life span increased, thanks to the greater abundance of food, but average height diminished. Skeletons also began to show a jump in calcium deficiency, anemia, bad teeth and bacterial infections. Most meat that people ate came from domesticated animals, which have more fat than wild game. Livestock also supplied early pastoralists with milk products, which are full of artery-clogging butterfat. But obesity still wasn't a problem, because even with animals to help, physical exertion was built into just about everyone's life.

That remained the case practically up to the present. It's really only in the past 100 years that cars and other machinery have dramatically reduced the need for physical labor. And as exercise has vanished from everyday life, the technology of food production has become much more sophisticated. In the year 1700 Britain consumed 23,000 tons of sugar. That was about 7.5 lbs. of sugar per capita. The U.S. currently consumes more than 150 lbs. of sweetener per capita, nearly 50% of which is high-fructose corn syrup that is increasingly used as a sugar substitute. Farmers armed with powerful fertilizers and high-tech equipment are growing enormous quantities of corn and wheat, most of which is processed and refined to be tastier and more convenient but is less nutritious. They are raising vast herds of cattle whose meat is laden with the fat that makes it taste so good. They are producing milk, butter and cheese by the tankerload, again full of the fat that humans crave.

And thanks to mass production, all that food is relatively cheap. It's also absurdly convenient. In many areas of the U.S., if you had a craving for cookies a century ago, you had to fire up the woodstove and make the dough from scratch. If you wanted butter, you had to churn it. If you wanted a steak, you had to butcher the cow. Now you jump into the car and head for the nearest convenience store--or if that's too much effort, you pick up a phone or log on to the Internet and have the stuff delivered to your door.

Unless you make a determined effort, you'll probably choose the path of least resistance. Evolving during a time of scarcity, humans developed an instinctive desire for basic tastes--sweet, fat, salt--that they could never fully satisfy. As a result, says Rutgers University anthropologist Lionel Tiger, "we don't have a cut-off mechanism for eating. Our bodies tell us, 'Fat is good to eat but hard to get.'" The second half of that equation is no longer true, but the first remains a powerful drive.

This doesn't necessarily mean we're doomed. There's no doubt that the obesity epidemic is real and our collective health has been getting progressively worse. Indeed, says Yale public-health expert Dr. David Katz, "today's kids may be the first generation in history whose life expectancy is projected to be less than that of their parents."

But the following pages will make it clear that there's plenty of reason for hope. Researchers are hard at work trying to understand the basic biochemistry of hunger and fat metabolism; policymakers are pushing for better labels and nutritional information; school boards are giving their cafeteria menus a closer look and reconsidering vending-machine contracts with makers of sugary soft drinks; urban planners are rethinking our cities and towns to get us out of the car and onto our feet; Americans in record numbers are putting themselves on low-carb and low-calorie diets; and more and more foodmakers are beginning to see increased awareness of the obesity epidemic not as a threat but as a business opportunity. It's too soon to tell if it's working, but there's at least one hopeful sign. For the first three quarters of 2003, there was no increase in obesity among adult Americans, according to preliminary data from the National Health Interview Survey.

Campaigns against smoking and drunk driving have raised the national consciousness about these public-health issues dramatically. There's no reason to think an anti-obesity campaign can't do so as well--as long as everyone involved acknowledges that the problem is real and that solving it will be as hard as anything we've ever done. After all, it's not easy to fight millions of years of evolution. --Reported by David Bjerklie/New York

With reporting by David Bjerklie/New York