By Gina Kolata, New York Times

Americans believe that obesity is the biggest health threat in the nation today — bigger even than cancer. But though a growing body of scientific research shows that diet and exercise are insufficient solutions, a large majority say fat people should be able to summon the willpower to lose weight on their own.

The findings are from a nationally representative survey of 1,509 adults released Tuesday by the National Opinion Research Center at the University of Chicago, an independent research institution. The study, funded by the American Society for Metabolic and Bariatric Surgery, found that concerns about obesity have risen. Just a few years ago, in a more limited survey, cancer was seen as the most serious health threat.

The lead researcher, Jennifer Benz of the survey group at the University of Chicago, said that to her knowledge no other survey has provided so comprehensive a view of Americans’ beliefs about obesity, including how to treat it, whether people are personally responsible for it and whether it is a disease.

Researchers say that obesity, which affects one-third of Americans, is caused by interactions between the environment and genetics and has little to do with sloth or gluttony. There are hundreds of genes that can predispose to obesity in an environment where food is cheap and portions are abundant.

Yet three-quarters of survey participants said obesity results from a lack of willpower. The best treatment, they said, is to take responsibility for yourself, go on a diet and exercise.

Obesity specialists said the survey paints an alarming picture. They said the findings went against evidence about the science behind the disease, and show that outdated notions about obesity persist, to the detriment of those affected.

“It’s frustrating to see doctors and the general public stigmatize patients with obesity and blame these patients, ascribing attributes of laziness or lack of willpower,” said Dr. Donna Ryan, an obesity researcher and professor emerita at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, who was not involved with the study. “We would never treat patients with alcoholism or any chronic disease this way. It’s so revealing of a real lack of education and knowledge.”

The self-help route has not been successful for most. Ninety-four percent of the survey participants who were obese had tried to lose weight with diet or exercise, to no avail. A quarter of those people said they had tried five to nine times and 15 percent said they had tried more than 20 times.

“Trying 20 times and not succeeding — is that lack of willpower, or a problem that can’t be treated with willpower?” asked Dr. Louis Aronne, director of the Comprehensive Weight Control Center at Weill Cornell Medicine and NewYork-Presbyterian, who was not involved with the study.

Obesity specialists said there are several reasons for obese people to seek medical help. There are factors, like side effects of certain medicines, that cause people to gain weight. There are also approved prescription drugs that help some people lose weight and keep it off. And for those with extreme obesity, there is surgery.

It’s not that diet and exercise are useless, noted Penny Gordon-Larsen, a professor of nutrition at the University of North Carolina and president of the Obesity Society, which studies obesity and its treatment. But lifestyle advice also depends on whether the issue is prevention or treatment and, if treatment, whether the person is extremely obese, obese or just overweight, she said.

“We need people to understand what options are there,” Gordon-Larsen, who was not involved with the study, said.

The study revealed that misconceptions about obesity treatment are pervasive. Sixty percent of respondents said diet and exercise are more effective than weight-loss surgery, which is the only method that elicits pronounced and sustained weight loss in nearly everyone with extreme obesity. Sixty-eight percent said it is safer to remain obese than to have weight-loss surgery, which has a lower mortality rate than gall bladder surgery or joint replacement.

Dr. Raul J. Rosenthal, president of the bariatric surgery society that funded the study, found this persistent belief in the power of diet and exercise hard to understand.

“If you think a disease is a potential killer, as serious as cancer, why would you take on its treatment and cure by yourself?” he asked. “The reaction of people to something that is a potential killer is mind-blowing.”

One problem, though, is that medical professionals can be as misinformed as the public, said Dr. Scott Kahan, an obesity medicine specialist who is an assistant professor at George Washington University and directs the National Center for Weight and Wellness, an obesity clinic.

Doctors, he said, learn nothing about obesity in medical school, which might be why only 12 percent of those in the survey with severe obesity said a doctor had suggested surgery to them. “We are talking about people who are 100, 200 pounds overweight,” Kahan added. Kahan, who is not a surgeon, noted that for most people that heavy, there is no other treatment that works.

Dr. Caroline M. Apovian, the president-elect of the Obesity Society and director of the nutrition and weight management center at Boston University, echoed Kahan’s concerns about the failure by doctors to mention the only effective course of treatment.

“If I said that was the case for cardiovascular disease and bypass surgery, you would say doctors are negligent,” she said.

To Learn More:

The ASMBS and NORC Survey on Obesity in America (National Opinion Research Center)

Obesity in U.S. Rises in Spite of Evidence of Healthier Diets (by Noel Brinkerhoff, AllGov)

Lack of Exercise Blamed in Income Disparity of Childhood Obesity (by Noel Brinkerhoff, AllGov)

Major Study Connects Plastic Packaging with Childhood Obesity (by Noel Brinkerhoff, AllGov)