University of Minnesota researchers say national obesity campaigns have not helped people recognize the health consequences of obesity.
They based their conclusion on more than 1 million health survey responses collected by the federal government over 30 years.
Study author Ross Macmillan said survey respondents were asked to self-report their weight, and then rate their health.
"In general people who are overweight think that they are in excellent health or very good health or good health," he said. "It hasn't changed over time. And then men in particular aren't likely to associate excess weight with poor health."
Macmillan said obese people may not believe they are in poor health because Americans are used to seeing overweight people in society, which makes the condition seem normal.
He also said weight-related illnesses tend to develop slowly and can usually be controlled with medication, which makes them seem less debilitating.
The study is published online in the Journal Obesity.