But while obesity may not be the Black Death, it is a severe public health crisis. Experts agree that as more and more obese children become obese adults, the diseases associated with obesity, such as heart disease, cancer, and especially diabetes will surge. That will mean a lot of sick people.

According to Marion Nestle, PhD, MPH, chair of the department of nutrition and food studies at New York University, the costs of these illnesses will be "astronomical."

James O. Hill, PhD, agrees. Hill, director of the Center for Human Nutrition at the University of Colorado Health Sciences Center, claims that at the rate we're going, obesity-related diabetes alone "will break the bank of our healthcare system."

So one has to wonder how obesity got so out of control that we reached this crisis. And more importantly, how do we stop it?

The Causes

So what's causing the epidemic? Not surprisingly, everyone agrees that it stems from two things: eating too much and exercising too little. The differences are in the specifics.

Although people may toss around the idea of genetics in obesity, genes can't really explain what's happening, Hill says. While a person may have a genetic predisposition toward a certain body type, the fact that each succeeding generation is heavier than the last proves that changes in our environment are playing the key role.

Hill believes the culprit may be a decrease in our physical activity, arguing that because of shifts in how we live and work, we don't get as much exercise as previous generations did.

Nestle agrees that exercise is important, but she lays more stress on eating habits. In her book Food Politics: How the Food Industry Influences Nutrition and Health , Nestle argues that recommendations about healthy eating are overwhelmed by the hundreds of billions of dollars worth of advertising for junk foods that we're subjected to at home and even in public schools. And as fast food companies and chains compete with one another by increasing portion sizes, our waists are increasing proportionately.

Visit the WebMD Weight Loss Clinic

The Numbers

Despite the new attention paid to obesity by doctors, researchers, and the media, no discernable progress has been made in fighting obesity. According to most experts, it looks almost certain that obesity will get worse before it gets better.

Cynthia Ogden, PhD, a CDC epidemiologist, published the results of a study of weight in the United States that she conducted with other experts. The results were startling: 31% of adults are obese and 15% of children and teenagers age 6-19 are overweight. The proportion of obese people has been growing steadily for the last few decades. Although Ogden stresses that obesity is a problem for all groups and genders, it is particularly severe among certain ethnic groups. For instance, 50% of all non-Hispanic black women are obese.

Did Ogden see anything promising in the results of the study about obesity in the U.S.? "I didn't see any hopeful signs," she says.

Conflicting Recommendations

The seemingly contradictory reports in the media about what people should and shouldn't be eating almost certainly don't help things. For instance, proponents of protein diets argue that all of the accepted wisdom about eating a low-fat diet is wrong. Most experts don't agree with them, but protein diets are being evaluated in studies now.

Where mainstream nutritionists and protein diet proponents agree is that the low-fat recommendations of the 1990s didn't quite work. "People took the low-fat message and decided that it meant that as long as they ate things that were low-fat, they could eat as much as they wanted," says William Dietz, MD, PhD, the director of the division of nutrition and physical activity in the National Center for Chronic Disease Prevention and Health Promotion at the CDC. That isn't the case, since calories add up, no matter what form they come in. Even worse, many of the low-fat snacks that companies developed actually had higher calories than their regular-fat equivalents, Dietz observes.

According to Nestle, the media also have a tendency of confusing things by reporting the results of scientific studies out of context. She argues that the relative stability of the dietary and fitness recommendations over the years -- eat less fat and more fruits and vegetables, exercise regularly -- is obscured by the media, which are more interested in exciting stories about radical diets or the effects of particular "miracle" foods or vitamins.

Surgical Options

An increasingly common treatment for severe obesity is bariatric surgery, such as "stomach stapling" in which the size of the stomach is surgically reduced. It's gotten a high profile as some obese celebrities and public figures have undergone the procedure with dramatic results. It's even becoming more common among teenagers. While bariatric surgery is necessary and life-saving in some cases, is it a reasonable treatment for obesity in America?

"Surgery is an effective last resort," says Dietz, "and many people are so obese, with a body mass index over 40, that they're at the last resort stage."

However, if obesity continues to worsen, so many people will require surgery that it will become impossible to operate on all of them. "It's difficult for me to see how we'll be able or willing to perform surgery on 100 million Americans," says Hill. Instead, the only real answer is in preventing people from getting to the point of surgery in the first place.

The Problems With Prevention

As with other public health campaigns, such as the efforts to get people to stop smoking or to practice safe sex, results of the campaign against obesity will come gradually. But Dietz sees reason for hope.

"I think that in the last three years, we've seen a dramatic shift in the attitudes of policy makers toward obesity," Dietz tells WebMD. "There is now a huge amount of attention being paid to the condition," he says, and that's an important first step.

But analogies to other public health efforts can only go so far, and obesity looks to be a difficult opponent. "Personally, I think that obesity may be the toughest social issue that we have ever faced," says Hill, "even more so than smoking."

Part of the problem is that the message about eating well is necessarily more complicated than the messages of other health campaigns. The recommendations for preventing tobacco-related illnesses are pretty straightforward: Don't smoke. But given that "don't eat" is not an option, there isn't such a concise recommendation for eating well and staying fit. It's more like, "Eat plenty of these, and not so much of that or those, and remember to exercise a lot."

And despite the increasing amount of attention paid to obesity in the media, recognizing and talking about it is difficult. Obesity can be a sensitive subject to discuss, given how stigmatized overweight people can feel. While no one would take offense if her doctor said she had high blood pressure or heart disease, she might very well be offended if her doctor said she was obese, since the word can sound like a moral as well as a medical judgment. According to anecdotal evidence, Dietz says that even people with severe obesity tend to think of the word as applying only to people much heavier than they are.

"I think that the American public still views obesity as a cosmetic problem," says Dietz. "The challenge is to get the public to recognize that this is a health problem and it's one that they can do something about." He also stresses that we need to come up with a different way of talking about obesity that won't make people feel stigmatized.

Visit the WebMD Weight Loss Clinic

Defeating Obesity

While it would be swell if every American woke up tomorrow and decided to exercise regularly and eat healthily, it's not going to happen and it's not that simple. "The trend in overweight is related to a lot of cultural, economic, and environmental factors," says Ogden, "and we need to work together to figure out what to do about it."

"The focus needs to be on environmental and policy solutions rather than individual behavior change," says Dietz. "Because it's changes in the environment that caused this problem and it's changes in the environment that will solve it."

The campaign against obesity will have to be massive, and it will have many fronts on a local and national level. Doctors need new ways to talk to their patients about obesity, says Dietz, and schools need new programs to encourage physical activity. Restaurants and fast food chains need to be encouraged to develop healthier foods. Nestle argues that concerned parents should try to reduce the amount of food advertising that their children are subjected to, and, if necessary, to lobby against school systems that serve soft drinks and fast food for lunch.

Dietz believes that beating obesity may even require a recasting of our entire healthcare system, since obesity needs to be prevented rather than treated after it happens. "We can't afford to treat obesity and its consequences," Dietz says. "So this begs the question whether it's time to move from a disease-care system to a real healthcare system."

Although all of these changes may seem radical, Dietz believes that they may be necessary to stop a potential health catastrophe. "We can't afford to think in traditional terms about obesity," he says.

What Should I Do?

While the news about preventing and treating obesity on a national scale may be depressing, it's important not to confuse a national health problem with your own, individual efforts to lose weight and live a more healthy life. While changing society may be tricky, changing yourself is considerably easier.

For instance, many people are able to lose weight and keep it off successfully, and even small reductions in weight can significantly decrease your health risks. Much of Hill's research has focused on the National Weight Loss Registry in Colorado, which Hill co-founded, that tracks the progress and habits of people who have lost weight and kept it off.

Hill reports that while people in the registry lost weight on all sorts of different diets, including protein diets, they tended to shift to a low-fat and high carbohydrate diet to maintain their weight loss. And on average, they exercised every day. While Hill stresses that most registry members say it wasn't easy, they almost uniformly believe that losing weight was worth the sacrifices.

So rather than get overwhelmed by depressing statistics or confused by competing theories of how to lose weight, it may be best to stick to the established recommendations about eating well and exercising regularly. Doing what you can might make a big difference.

By R. Morgan Griffin
Reviewed By Kathleen Zelman, MPH, RD, July 25, 2007.
Published Dec. 26, 2002.
Medically updated July 25, 2007.

SOURCES: William H. Dietz, MD, PhD, director of the division of nutrition and physical activity, National Center for Chronic Disease Prevention and Health Promotion at the CDC. James O. Hill, PhD, professor of pediatrics and director of the Center for Human Nutrition at the University of Colorado Health Sciences Center, Denver, co-founder of the National Weight Control Registry. Marion Nestle, professor and chair of the department of nutrition and food studies, New York University, author, Food Politics . Cynthia Ogden, PhD, epidemiologist, CDC.