Meal Size, Not Body Size, Explains Errors in Estimating the Calorie Content of Meals

5 September 2006 | Volume 145 Issue 5 | Pages 326-332

Background: Although most people underestimate the calories they consume during a meal or during the day, calorie underestimation is especially extreme among overweight persons. The reason for this systematic bias is unknown.

Objective: To investigate whether the association between calorie underestimation and body mass reflects a tendency for all persons to underestimate calories as the size of a meal increases.

Design: Overweight and normal-weight adults estimated the number of calories of a fast-food meal they had ordered and eaten (study 1) or of 15 fast-food meals that were chosen by the experimenter (study 2) in a randomized, controlled trial. Their estimations were compared with the actual number of calories of the meals.

Setting: Study 1 was a field study conducted in fast-food restaurants in 3 medium-sized midwestern U.S. cities. Study 2 was conducted in a laboratory at a major U.S. research university.

Participants: Study 1 involved 105 lunchtime diners (average body mass index [BMI], 24.2 kg/m² [range, 17.2 to 33.5 kg/m²]). Study 2 involved 40 undergraduate students (average BMI, 23.2 kg/m² [range, 16.1 to 32.3 kg/m²]).

Measurements: Participants were asked to estimate the number of calories in a fast-food meal they had ordered and eaten (study 1) or in 15 sizes of the same fast-food meal (study 2). The actual number of calories in the meals in the field study was obtained by unobtrusively recording the food that was ordered (identified from the wrappings and containers). Weight and height were self-reported.

Results: Although participants strongly underestimated the number of calories in larger meals (by –38.0% in study 1 and by –22.6% in study 2), they almost perfectly estimated the number of calories in smaller meals (by –2.9% in study 1 and by 3.0% in study 2). After the authors controlled for body weight–related differences in meal size, the calorie estimations of normal-weight and overweight participants were identical in both studies.

Limitations: These studies examined fast-food meals. Weight and height were self-reported. There were too few observations to distinguish between obese (BMI 30 kg/m²) and overweight (BMI >25 kg/m² but <30 kg/m²) participants.

Conclusions: Greater underestimation of calories by overweight persons is a consequence of their tendency to consume larger meals. Calorie underestimation is related to meal size, not body size.

Editors' Notes Context The ability to estimate the calorie content of meals is important for reducing food intake. Contribution Trained interviewers asked fast-food restaurant customers to estimate the calorie content of their meals. Interviewers counted the empty food containers on each participant's tray and calculated the meal's actual calorie content from the posted calorie content of each item. People, regardless of their weight, estimated normal-sized meals accurately. Likewise, everyone underestimated large meals. Overweight people were more likely to order larger meals and therefore to make larger errors. Cautions Participants were young adults. Implications Everyone tends to underestimate the calorie content of large meals. —The Editors

 

Author and Article Information

From Cornell University, Ithaca, New York, and INSEAD, Fontainebleau, France.

Acknowledgments: The authors thank James E. Painter, Jill North, and Jennifer Wansink for their help with data collection in the pilot study.

Grant Support: None.

Potential Financial Conflicts of Interest: None disclosed.

Requests for Single Reprints: Brian Wansink, PhD, 110 Warren Hall, Cornell University, Ithaca, NY 14853-7801.

Current Author Addresses: Dr. Wansink: 110 Warren Hall, Cornell University, Ithaca, NY 14853-7801.

Dr. Chandon: INSEAD, Boulevard de Constance, 77300 Fontainebleau, France.

Author Contributions: Conception and design: B. Wansink, P. Chandon.

Analysis and interpretation of the data: B. Wansink, P. Chandon.

Drafting of the article: B. Wansink, P. Chandon.

Critical revision of the article for important intellectual content: B. Wansink, P. Chandon.

Final approval of the article: B. Wansink, P. Chandon.

Provision of study materials or patients: B. Wansink, P. Chandon.

Statistical expertise: B. Wansink, P. Chandon.

Administrative, technical, or logistic support: B. Wansink, P. Chandon.