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Heavy or Lean, People Tend to Underestimate Calories in Big Portions

Sept. 7, 2006 -- Attention calorie counters: When sizing up to a big meal, you might want to double your calorie estimate.

Most people underestimate calories in large meals, even if they're not overweight, researchers report in the Annals of Internal Medicine.

"All persons strongly underestimate large meals and large portions," write Cornell University's Brian Wansink, PhD, and colleagues.

They add that the consequences might be more serious for overweight people, who tend to eat bigger portions than leaner people.

In their study, Wansink's team created two calorie-counting challenges, tracked the test subjects' errors, and came up with a set of practical solutions.

Their bottom line: If you're sitting down to a feast, double your calorie budget.

Calorie Check

First, the researchers interviewed 105 customers aged 18 and older at fast-food restaurants in three Midwestern cities.

Participants estimated the calories in their meals, including the leftovers.

The participants also reported their height and weight; 59% were normal weight and 41% were overweight, based on BMI (body mass index), which relates height to weight.

The diners correctly gauged the calories in the 52 smallest meals.

But those who ordered the 53 largest meals made calorie estimates that were 38% too low.

Overweight people were more likely to have bigger portions. When the researchers took that into account, diners of all sizes were equally clueless about calories in big meals.

Missing the Mark

Next, the researchers headed to an unnamed U.S. university, stopping along the way at a local fast-food restaurant to buy chicken nuggets, fries, and cola.

Back at the university, they arranged the food into 15 meals of different sizes on paper plates.

The researchers showed the meals to 40 undergraduate students and asked the students to gauge the calories in each meal.

The students' calorie estimates were accurate for the eight smallest meals and 22% too low for the seven largest meals.

According to the students' self-reported height and weight, 70% of the students had normal BMI and 30% were overweight. The results were the same for heavier and lighter students.

The study has some limitations. For instance, no one made sure participants told the truth about their height and weight.

When people misstate their weight, they usually lowball. When the researchers took that into account, the results didn't change.

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