(CNN) — Calorie counting has long been touted as an effective tool for losing pounds or maintaining a healthy weight. But new research published in the British Medical Journal shows many of us are underestimating the calories we’re eating, especially when we visit fast food restaurants.
Researchers interviewed more than 1,800 adults, 1,100 adolescents and 330 children at several fast food chains in New England. The interviews were done at McDonald’s, Burger King, Subway, KFC, Dunkin’ Donuts and Wendy’s around dinnertime and lunchtime.
Study participants were asked to estimate their meal’s calorie count. Researchers then collected the bill to later tally the correct amount of calories using nutrition info posted on the chain’s website.
At least 40% of the study participants reported eating at the restaurant where they were interviewed at least once a week. More than 20% of the adult participants noticed posted calorie information, but only 5% said they used that information when purchasing food.
The mean calorie count for adults’ meals was 836 calories; teens purchased 756 calories and children ordered 733 calories. “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,” the study authors write.
Adults tended to underestimate their meals by about 175 calories, the same as children. Adolescents were more likely to underestimate by about 250 calories. Adults with a higher BMI were less likely to underestimate than their normal weight counterparts.
The restaurant most likely to confuse calorie-counters? Subway. Adult diners there underestimated their consumption by an average of 350 calories and teen diners underestimating by an average of 500 calories. Most of Subway’s 6-inch sandwiches contain between 350 and 500 calories; consumers must double that if they order a foot-long sub and factor in extra calories for sides and/or drinks.
More than half of the people researchers approached were unwilling to participate. Researchers also did not interview anyone going through the drive-thru. The people they did not talk to may have estimated their calorie counts differently than the study population.
The researchers also did not weigh each participant’s food to determine its exact calorie amount, instead relying on generalizations from the restaurant’s website.
The study authors are hopeful that listing calorie counts on menus in these establishments will encourage consumers to make healthier choices. But research on the effect of calorie displays has been mixed.
More important may be the sheer number of calories consumers are eating in a typical fast food meal. Depending on their age, children need between 1,200 and 2,000 calories per day. Eating more than 730 in one sitting (and remember, that’s the mean — others ate up to 350 calories more than that) could lead to weight gain over time.
Experts recommend doing some research before you order out. View the restaurant’s nutritional info online and decide what you’ll eat ahead of time.