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We’re lousy at estimating fast-food calories

Most of us underestimate — often significantly — the calorie content of foods we eat in fast-food restaurants, according to a Harvard study, 

Most of us underestimate — often significantly — the calorie content of the burgers, sandwiches, fried chicken, salads, milk shakes and other foods we eat in fast food restaurants.

Think you know how many calories were in that fast-food meal you gobbled down at lunch yesterday?

Think again. Most of us underestimate — often significantly — the calorie content of the burgers, sandwiches, fried chicken, salads, milk shakes and other foods we eat in fast food restaurants, according to a study published Thursday by Harvard University researchers.

Yes, other studies have shown that people tend to underestimate the amount of calories in their fast-food meals. But those studies were conducted in laboratory settings. This new study collected its data in real-world environments: 89 McDonald’s, Burger King, Wendy’s, KFC, Subway and Dunkin’ Donuts restaurants in four New England cities.

For the study, which was published in the journal BMJ, researchers offered diners going into those restaurants a $2 gift card if they would keep their receipt and participate in a study about fast-food choices after they had finished purchasing and eating their food. That participation involved filling out a questionnaire that asked the diners to estimate the calorie content of the meals they had just finished. In all, 1,877 adults, 1,178 teenagers and 330 parents of school-aged children participated. (The parents were asked to estimate the calories in the meals they had purchased for their children.)

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Based on the receipts, the average (mean) calorie content of the meals was 836 for adults, 756 for teens and 733 for children. But the participants tended to believe the meals were leaner.

“At least two-thirds of all participants underestimated the calorie content of their meals,” the study’s authors write, “with about a quarter underestimating the calorie content by at least 500 calories.”

The adults underestimated their meals and the meals of their school-aged children by an average of 175 calories, and the teens underestimated their meals by an average of 259 calories.

A couple surprises

Interestingly, the adults with higher body mass indexes (BMIs) — those who were overweight or obese — tended to be more accurate about the calorie counts.  (In the study, 64 percent of the adult participants were either overweight or obese, as were 34 percent of the teens and 57 percent of the school-aged children.)

Also surprising was the finding that Subway diners were the most likely to underestimate the calories in their fast-food meals. In fact, adults eating at Subway were 20 percent more likely to underestimate than those eating at McDonald’s. This may be because of Subway’s successful efforts to brand itself as offering healthier meals than its competitors — what the Harvard researchers call a “health halo” effect.

The study was conducted in 2010 and 2011. At that time, none of the chain restaurants in the study routinely printed calorie contents on their menus. Some did, however, post the calories in items they were promoting as “low-calorie.” But less than 5 percent of the study’s participants said they had noticed those postings.

ACA will bring more calorie listings

The Affordable Care Act, passed by Congress in 2010, requires restaurant chains with more than 20 locations to post the calorie contents of its meals, starting in 2014. The Food and Drug Administration is still drafting rules about how those calorie postings should be done. Some restaurants have, of course, gone ahead with their own listings, often to comply with local laws.

This study suggests that many of us need those listings — if we want to keep control of the calories we’re consuming.

Of course, a better idea would be not to eat at fast-food restaurants at all. That doesn’t seem a likely option for many people, however. Surveys have found that 44 percent of Americans eat at a fast-food restaurant at least once a week, and 20 percent eat at such establishments at least three times a week.

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You can read the Harvard study on the BMJ website.