People often underestimate calories in big portions

NEW YORK (Reuters Health) - While people have a good sense of the calories contained in smaller portions of fast food, they sharply underestimate the calories in "super size" servings, research hints.

In the study, people who chose a smaller-size fast food meal guessed it contained 419 calories, on average, which was not far off the mark, given that the actual calorie content was 514. However, people who picked a larger serving estimated its calorie content at 675 calories, when in reality the calorie count was 1,188.

Almost everyone underestimates the amount of calories they consume, and people who weigh more do so to a greater degree, but it's not clear why, Dr. Brian Wansink of Cornell University in Ithaca, New York and Pierre Chandon of the graduate business school INSEAD in Fontainebleau, France note in a report released this week.

The researchers hypothesized that the difference might occur because it's easier to estimate calorie content of smaller meals, while heavier people will choose larger meals and thus have more trouble gauging how many calories these meals contain.

To investigate, they performed two experiments. In the first, they asked 105 people eating in a fast food restaurant to estimate the amount of calories contained in the meal they had just eaten. In the second, 40 students were asked to gauge the calorie content of 15 different portion sizes of a meal of chicken nuggets, French fries and cola.

Study participants gauged calorie content of smaller meals much more accurately, with guesses within 3 percent of the actual calorie content. In contrast, they underestimated larger meals' calorie content by 38 percent in the first part of the study, and by about 23 percent in the second.

The findings disprove the idea that overweight people underestimate the amount of calories they eat because they are in denial or want to hide their eating habits from others, Wansink and Chandon conclude. Instead, both normal- and overweight people misperceive calories contained in larger portions, and heavier people are more likely to choose big portions.

"Exhorting good-faith overweight persons to pay more attention to their meals or to stop lying to themselves and to their physicians is unfounded and probably is counterproductive," they write.

A better approach, they conclude, would be to help people find more effective ways to gauge the calorie content of larger portion sizes.

SOURCE: Annals of Internal Medicine, September 5, 2006.