According to the LiveScience Website, Harvard Medical School researchers who surveyed more than 3,000 customers — adults, teenagers and parents with young children — at fast food stores in New England found that about two-thirds thought there were fewer calories in the meals they purchased than there actually were.
 

The researchers approached customers — at McDonald's, Burger King, Subway, Wendy's, KFC, and Dunkin' Donuts — and asked how many calories they thought were in their meals (or, for parents, in their kids' meals). They then viewed the customers' receipts to verify what was purchased.
 

On average, adults underestimated the calorie content of their food by 175 calories, teens misjudged by 259 calories, and parents miscalculated their children's meals by 175 calories.
 

The findings, presented at a meeting of the American Public Health Association in Boston this week, also indicated people were more likely to underestimate calories if they had a big meal, or overestimated how many calories they believe they need to consume in a day, compared to expert recommendations.
 

The researchers, led by Harvard professor Jason Block, M.D., said they don't know why people have more trouble estimating the calorie content of food from some chains. But it's possible that marketing campaigns — like those launched recently by Subway — have attempted to spotlight newer, healthier options on fast-food menus.
 

Under new Obamacare provisions, restaurant chains with more than 20 locations will soon be required to post calorie information on menus (the Food and Drug Administration is still finalizing the regulations).
 

Placing calories on restaurant menus throughout the country will be a big experiment, and researchers will be looking to see if it changes consumers' choices, Dr. Block said.

But even if it has no effect on consumer habits, he said it may cause some chains to alter their menu. He added that it may already be having an impact, noting Burger King started selling low-calorie fries.