Meal Size More Important Than Calorie Content

Abstract & Commentary

By Mary Elina Ferris, MD, Clinical Associate Professor, University of Southern California. Dr. Ferris reports no financial relationship to this field of study.

Synopsis: Both overweight and normal-weight persons underestimated calorie content of large meals but not smaller meals. Since overweight persons ate larger size meals, they consumed more unnecessary calories.

Source: Wansink B, et al. Meal size, not body size, explains errors in estimating the calorie content of meals. Ann Intern Med. 2006:145;326-332.

Customers at fast-food restaurants in 3 mid-western US cities during 9 weekday lunch hours were asked to estimate calorie content of their food choices at the end of the meal, while the researchers unobtrusively recorded actual known calorie content previously established for that serving size. This was then correlated with their self-reported height and weight. Participants averaged 20 years of age, and underestimated calories by an overall average of 23%. However, the estimates of small size meals were accurate to within 2.9%, while larger meals had increasing disparity of 38% in actual calories compared to known amounts. Calorie estimations of overweight persons (BMI, 25 or greater) compared to others was not statistically different, but their meal choices contained significantly more calories overall (average, 957 compared to 683 calories).

To evaluate for bias of self-selection from this restaurant survey, a similar study was repeated in a college laboratory using food items with pre-determined portion and calorie sizes. Students successfully estimated the calorie content of small portions within 3%, but underestimated an average of 23% for larger sizes. These estimates were not statistically different for overweight compared to normal-weight persons.


It behooves us all to understand the factors behind the epidemic of obesity sweeping the country. The trends of higher calorie counts and larger portion sizes in most prepared foods have been widely publicized, but what factors compel some persons to choose and consume larger amounts than others? Previous research has shown that obese persons consistently underestimate the actual calorie content of their meals,1 interfering with their attempts at dieting.

This straightforward study, performed without any external grant support, demonstrates that persons of every weight have more problems estimating calorie content in larger size portions than in smaller sizes. Another study by the same author showed this is true even with nutrition experts.2 Obese persons (at least for the young age utilized in this study) have no inherent difference in their ability to estimate calorie counts. For our patients struggling with weight loss, this knowledge and the advice to choose small size portions in small containers may help them achieve their goals.


1. Lichtman SW, et al. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. N Engl J Med. 1992;327:1893-1898.

2. Wansink B, et al. Ice cream illusions bowls, spoons, and self-served portion sizes. Am J Prev Med. 2006;31:240-243.