How We Grew So Big
Diet and lack of exercise are immediate causes—but our problem began in the Paleolithic era
By Michael D. Lemonick

BIBLIOTHEQUE DES ARTS DECORATIFS/ARCHIVES CHARMET/BRIDGEMAN ART LIBRARY

June 7, 2004
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.

	How Do the Diets Stack Up? Any diet book will help you lose weight if you stick to the plan, but the theories behind them vary widely.
	The Fat Five The list of factors that have conspired to make us fat is a long one, but experts put these five at or near the top.
	Views on Obesity in the U.S. TIME / ABC NEWS Poll
	Body Mass Calculator Body mass index measures body fat based on height & weight
	• The Obesity Epidemic • A Different Kind of Education • The Inactive Generation
	• Conference Website • Webcast

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.

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