According to a series of new Cornell studies, many people also tend to underestimate just how many calories healthy restaurant foods contain by 35 percent.
"We found that when people go to restaurants claiming to be healthy, such as Subway, they choose additional side items containing up to 131 percent more calories than when they go to restaurants like McDonald's, that don't make this claim," said Brian Wansink, author of "Mindless Eating: Why We Eat More Than We Think" (Bantam 2006) and the John S. Dyson Professor of Marketing and of Applied Economics and director of the Cornell Food and Brand Lab.
The authors also reported that by simply asking people to reconsider restaurants' health claims urges them to better estimate calories and not to order as many side dishes. They suggested that public policy efforts help people to better estimate the number of calories in foods.
"In estimating a 1,000 calorie meal, I've found that people on average underestimate by 159 calories if the meal was bought at Subway than at McDonald's," Wansink said.
He said that since it takes an energy imbalance of 3,500 calories to put on one pound, that extra 159 calories could lead to almost a 5-pound weight gain over a year for people eating at Subway twice a week compared with choosing a comparable meal at McDonald's with the same frequency.
He therefore said that these studies help explain why lower-calorie menus at fast-food restaurants have not led to the expected reduction in total calorie intake and in obesity rates.
The new research is published in the October online version of the Journal of Consumer Research.