The key to counting calories: portion size!

There has been research reporting that those who are overweight will generally underestimate they number of calories that they eat. This has often been cited as one of the contributing factors to the increasing issue with overweight and obesity. Brain Wansink and Pierre Chandon, at the Cornell University Food and Brand Lab, set out to challenge this view and in research reported in the Annals of Internal Medicine they present their very interesting findings (Ann Intern Med 2006;145(5):326-332).

The researchers designed a two part study. They first approached diners in fast food restaurants and asked them to self-report on their height and weight and then estimate the number of calories in the meal that they had just consumed. The interviewers had been watching and recording what the participants had eaten.

The interesting finding was that all of those interviewed underestimated the number of calories by an average of 23%. When the researchers looked at the estimates of larger meals vs. smaller ones they found that when eating a smaller meal people were able to pretty accurately estimate the number of calories they had eaten. This wasn't the case with larger meals where calories consumed were underestimated by a whopping 38% (or maybe I should say a Whopper®).

To confirm these findings, Wansink and Chandon designed a laboratory experiment where they asked students to rate 15 different meals for the amount of calories. The meals were different combinations of chicken nuggets, fries and cola and ranged from 445 to 1780 calories.

While the calorie estimates were not as wide of the mark as with those questioned in fast food restaurants, participants in the lab did underestimate the calories in meals by an average of 9%. The researchers found similar results for super-sized vs. normal sized meals, in that the participants thought the larger meals contained 26% fewer calories than the actual amount. As in the first part of the study, they were able to accurately report the number of calories in the normal sized meal.

The most interesting part is that in both the field and lab studies, the participants' Body Mass Index didn't make a difference in their perception of how many calories were in food. The difference was that in the first part of the study the overweight people were more likely to choose the larger meal. Consequently, it is the choice of a larger meal, that people feel contains fewer calories, that leads to over-consumption.

What this means for you:

Portion size is once again proven to be key in eating healthy no matter what your weight. If you are going to eat fast food, choose the regular sized meal. Here's a guide to some healthier choices at different fast food joints.

First posted: September 13, 2006