More than three-quarters of obese Americans say they have healthy eating habits, according to a survey of more than 11,000 people.

About 40 percent of obese people also said they do "vigorous" exercise at least three times a week, the telephone survey found.

"There is, perhaps, some denial going on. Or there is a lack of understanding of what does it mean to be eating healthy, and what is vigorous exercise," said Dr. David Schutt of Thomson Medstat, the Michigan-based health-care research firm that conducted the survey.

The survey also found that 28 percent of obese people reported snacking two or more times a day, only slightly more than 24 percent of normal weight people who said they did.

But the survey failed to ask people what — and how much — they ate, noted Dr. Jeffrey Koplan of Atlanta's Emory University.

"The questions leave out quantity," said Koplan, who chairs an Institute of Medicine committee on progress in preventing childhood obesity.

Roughly two-thirds of Americans are overweight or heavier, and nearly one-third qualify as obese, according to the U.S. Centers for Disease Control and Prevention.

Respondents to the survey were contacted through computer random digit dialing in January through March. The surveyors relied on the respondents to be truthful about their height, weight and other answers.

Obesity was determined by body-mass index, a calculation based on height and weight. Using BMI, a man 5-feet-10 would be considered overweight at 174-208 pounds, and obese at 209 pounds or more.

About 3,100 of the people in the survey were obese or morbidly obese; an estimated 4,200 more people were overweight; about 3,800 were normal weight and about 200 were underweight, according to the Thomson Medstat.

Those demographics are generally consistent with the federal health survey that actually measures and weighs people, said Schutt, the company's associate medical director.

It was surprising how some responses from obese and overweight people paralleled those of thinner respondents.

For example, about 19 percent of obese people said they always read nutritional labels on food packages, compared with 24 percent of normal-weight people. And about 29 percent of obese people said they eat out at restaurants three or more times a week, compared with 25 percent of normal-weight people.

"The numbers aren't wildly different," Schutt said.

One of the largest differences was the answer to the question: How often do you eat all of the food you are served at restaurants? About 41 percent of obese people said they always did, while 31 percent of normal weight people always did.

Thomson Medstat is a data collection and analysis company that contracts with the federal government and about 20 states, on health projects. The data about eating and exercise are part of a larger package of survey information being marketed to employers, hospitals and other customers. It is not being published in a peer-reviewed scientific journal.

The survey had a sampling margin of error of plus or minus 1 percentage point, according to the company.