When people eat at a fast-food joint they tend to drastically underestimate the amount of calories they’re getting, a new Harvard Medical School survey found. The survey included interviews with more than 3,000 people who ate at six different fast-food chains in 2010 and 2011.
“At least two thirds of all participants underestimated the calorie content of their meals, with about a quarter underestimating the calorie content by at least 500 calories,” Harvard’s Jason Block and colleagues wrote in the British Medical Journal.
On average people thought they were eating 175 fewer calories than they actually were. To put that in perspective, if you overate that much once a day, over the course of a year you’d gain 18 extra pounds!
Ironically, people were more likely to underestimate calories when eating at Subway compared to places like McDonald’s and KFC. Researchers suspect that’s because Subway advertises itself as being a healthy food option, creating a so-called “health halo” effect. This effect leads people to think that foods with healthy labels have fewer calories than they really do, and as a consequence they eat more of them.