Most people ingest more calories when dining at so-called healthy restaurants, according to new research from Cornell University.

Researchers say healthy restaurants often prompt consumers to treat themselves to higher-calorie side dishes, drinks or desserts than they would normally eat at fast-food and other restaurants that do not claim to be healthy.

The research, published in the October online version of the Journal of Consumer Research, found that many people also tend to underestimate by 35 percent just how many calories those so-called healthy restaurant foods contain.

"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, Cornell's John S. Dyson professor of marketing and applied economics and director of the Cornell Food and Brand Lab, in a news release.

Wansink and co-author Pierre Chandon, a marketing professor at INSEAD, an international business school in France, also reported that simply asking people to reconsider restaurants' health claims prompts them to better estimate calories and not to order as many side dishes.

"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," said Wansink.

That extra 159 calories could lead to an almost five-pound weight gain over a year for people eating at Subway twice a week compared to choosing a comparable meal at McDonald's with the same frequency, he said.

These studies, he added, 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 authors recommend that public policy efforts help people to better estimate the number of calories in foods.