Senior author Brian Wansink of Cornell University, executive director of the U.S. Department of Agriculture's Center for Nutrition Policy and Promotion, and Pierre Chandon, of INSEAD, a business school in France, said that the French use internal cues -- such as no longer feeling hungry -- to stop eating.

Americans tend to use external cues -- such as whether their plate is clean, they have run out of their beverage or the TV show they're watching is over, Wansink said.

The study, an analysis of questionnaires from 133 Parisians and 145 Chicagoans about how they decide when to stop eating, may explain why body mass index varies across people and potentially across cultures, the study said.

"Furthermore, we have found that the heavier a person is -- French or American -- the more they rely on external cues to tell them to stop eating and the less they rely on whether they felt full," Wansink said in a statement.

The findings are published in the journal Obesity and are being presented this month at an the Winter Marketing Educators conference.