In the minutes before her mother's car returned, the terrified girl looked toward the nearby houses on the suburban Philadelphia street and wondered if she should walk over and ask for help.

"But I didn't," said McAfee, 62, who is now the director of medical advocacy for the Council on Size and Weight Discrimination. "I didn't think anyone would want a fat child."

The stigmatization of obesity begins in preschool: Children as young as 3 tell scientists studying the phenomenon that overweight people are mean, stupid, ugly and have few friends. It intensifies in adulthood, when substantial numbers of Americans say obese people are self-indulgent, lazy and unable to control their appetites. And it translates into poorer job prospects for the obese compared with their slim peers.

It may be the nation's last, accepted form of prejudice. But the stigmatization of obesity has repercussions beyond the pain it inflicts on its targets: It threatens to impede efforts to fight the obesity epidemic.

"As long as we have this belief that obese people are lazy and lacking in discipline, it will be hard to get support for policies that change the environment, which are likely to have a much larger impact than trying to change individuals," said psychologist Rebecca Puhl of the Rudd Center for Food Policy & Obesity at Yale University in New Haven, Connecticut.

That barrier to action is becoming clearer as the nation grapples with the costs of having two-thirds of adults overweight or obese. This week, an influential health panel proposed changes to an obesity-promoting environment, from farm policies to zoning, trying to shift the debate away from personal blame.

A new Reuters/Ipsos online poll of 1,143 adults from May 7 to 10 captures some of the prejudicial attitudes. Asked to identify the main cause of the epidemic, 61 percent chose "personal choices about eating and exercising"; 19 percent chose the actions of food manufacturers and the fast-food industry. The poll is accurate to within 3.6 percentage points. Because of the methods used to collect the data, accuracy is measured using a statistical measure called a credibility interval.

Reflecting the belief that the obese have only themselves to blame, 49 percent of respondents favored allowing insurers to charge obese people more for health insurance.

Poll respondents also showed broad support for efforts that target the food industry: 56 percent wanted to limit advertising of unhealthy food or taxing sugared soda, 77 percent were in favor of calorie counts at restaurants and sport arenas. But an all-out ban on fast-food restaurants? America loves its Big Macs: Only 21 percent said yes.

EFFECTS OF THE STIGMA

One effect of the obesity stigma is that discrimination on the basis of weight is legal. Michigan is the only state that prohibits it, along with a few towns and cities. Everywhere else, it is legal to deny people jobs or refuse to rent them an apartment if they are obese. The fact that two-thirds of American adults are overweight or obese has not led to bans on such discrimination.

That does not surprise McAfee, who weighs about 500 pounds. "Studies show that fat people are even more prejudiced against fat people" than thin people are, she said.

Even respected leaders such as New Jersey Governor Chris Christie, seen as a potential running mate for Republican presidential hopeful Mitt Romney, are not spared the mockery.

Christie's girth was the target of fat jokes at the White House Correspondents' dinner last month, though he shrugged them off.

"When you're overweight, fair or unfair, there's going to be those who make really awful comments about you and there are going to be people who make jokes about it. That's the way it goes," Christie told reporters.

The stigma also hurts the efforts of America's 73 million obese adults and 12 million obese children to get back to a healthy weight: Targets of stigma often fall into depression or withdraw socially. Both make overeating, binge eating, and a sedentary existence more likely, studies show.

Sophie Lewis and her colleagues at Monash University in Australia interviewed hundreds of obese adults who were the target of such comments as "look at that fat lady!" when out in public. As a result, found Lewis, obese people are less likely to exercise by walking outdoors.

Even healthcare professionals hold negative attitudes about the obese, studies show. Physicians often spend less time with an obese patient, for instance, and do not counsel them about a healthy lifestyle, perhaps believing it would fall on deaf ears.

Doctors and nurses who telegraph negative attitudes toward the obese can keep them from seeking treatment for diabetes, found a study led by Elizabeth Teixeira of Drexel University College of Nursing and Health Professions in Philadelphia.

"Patients are afraid of hearing, 'you're fat,' or 'just lose weight,' as if it were that easy," said Teixeira, a nurse practitioner specializing in diabetes. "I've had patients tell me they delay seeking care, even having their blood pressure or glucose checked, because they don't want to be lectured."

A 2010 study by scientists at Johns Hopkins University in Baltimore found that the fatter a patient, the more likely a doctor is to assume he or she is not taking medications as prescribed. That, other studies have shown, can keep physicians from prescribing needed meds, assuming they won't be taken.

Taking all that data into account, it may not be surprising how reluctant people are to call themselves obese. In the Reuters/Ipsos poll, 14 percent of respondents said they are obese. Based on their self-reported height and weight, 26 percent are obese according to U.S. guidelines.

SHIFTING THE DEBATE

The belief that obesity reflects personal decisions implies that the solution, too, should be personal: Eat less, move more. But as the Institute of Medicine argued this week, the most effective way to combat obesity is to change the environment.

For average American adults, willpower is no match for "an environment in which we are constantly bombarded by food and food cues," said David Kessler, former head of the Food and Drug Administration and author of the 2009 book, "The End of Overeating: Taking Control of the Insatiable American Appetite." "Lecturing people doesn't work."

The IOM recommended building sidewalks to make it easier for people to walk, banning sugary drinks from schools and requiring 60 minutes of daily exercise in grades K-12, reducing portion sizes in schools and restaurants, and making low-cal choices widely available and as affordable as super-sized ice cream cones. Most important, it concluded, was changing the "messaging," including the ubiquitous marketing of calorie-dense food.

Fat stigma makes those ideas ripe for attack by an industry that says how much to eat and move reflects individual choice. The restaurant- and food-industry-funded Center for Consumer Freedom called the IOM "arrogant and absurd" for suggesting "that Americans are too stupid to make their own food choices." By proposing to keep unhealthy, calorie-dense food out of school lunch programs, it said, "food nannies" like the IOM are "flatly arguing against consumers having any choice in their snacks and meals."

In the Reuters/Ipsos poll, respondents were almost evenly split over "government intervention" to reduce obesity, with 52 percent supporting it and 48 percent opposing it. There was greater support for specific steps, with 87 percent in favor of requiring 30 minutes per day of exercise in school.

ROOTS OF THE STIGMA

Psychologist Chris Crandall of the University of Kansas has found that young adults who stigmatize obesity tend to be more ideologically conservative, favoring traditional sex roles and capital punishment, his studies found.

"Particularly in America, self-determination and individual choice is a fundamental value," he said. "We blame people for everything that happens to them - being poor, being obese. It's the ‘just world' idea that people get what they deserve."

The stigma is less pronounced in countries such as India, Mexico and Turkey, whose cultures assign more collective responsibility for personal outcomes, Crandall found. His studies, going back to the 1990s, surveyed hundreds of people worldwide about how closely they associate obesity with adjectives such as lazy and stupid.

Americans also stand out in their conviction that hard work and determination lead to success, while failure is due to lack of effort.

"Being thin has come to symbolize such important values as being disciplined and in control," said Yale's Puhl. The converse: If someone is not thin, he must be lacking in those virtues.

Indeed, some Americans value thinness more than life itself. In a 2007 study, 24 percent of women and 17 percent of men said they would trade three or more years of life to be svelte.

Yet despite the rising personal stakes, a growing body of research shows just how hard it is for the average person to keep the pounds off.

Just before speaking to Reuters, McAfee had exercised for an hour in her Florida pool and had a salad for lunch.

"I work out, I eat a lot of fruits and vegetables, and I'm still not thin," she said. "So please stop beating the crap out of me: It's completely counterproductive."

(Additional reporting by Edith Honan; Editing by Michele Gershberg and Prudence Crowther)

• A Permanent Economic Emergency