One night when Lynn McAfee was 5 years old, her psychologically troubled mother left her at the side of a road as punishment for a now forgotten infraction.

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.