'As soon as you tell people to eat supplemental foods, people think there are free calories and there are not,' said Frank Sacks, professor of cardiovascular disease prevention at the Harvard School of Public Health.

This is a particularly American way of thinking about food, said Greg Critser, author of 'Fat Land: How Americans Became the Fattest People in the World.'

'The Europeans don't have this mentality,' Mr. Critser said. 'There's more a culture of the enjoyment of food, not just the amount of food. The problem is that behind whatever diet is in ascent in this country, the background noise is one and the same: a license to gluttony.'