But just seven-in-ten say this about "the people they know." And just under four-in-ten (39%) say they themselves are overweight.

These sliding assessments are drawn from a Pew Research Center telephone among a randomly selected, representative national sample of 2,250 adults. The survey finds that most Americans, including those who say they are overweight, agree that personal behavior - rather than genetic disposition or marketing by food companies - is the main reason people are overweight. In particular, the public says that a failure to get enough exercise is the most important reason, followed by a lack of willpower about what to eat.

About half the public also says that the kinds of foods marketed at restaurants and grocery stores are a very important cause, and roughly a third say the same about the effect of genetics and heredity.