Americans believe that obesity is tied with cancer as the biggest health threat in the nation today. But though 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 on Tuesday by NORC 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 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.