The study, "Frosting on the cake: pictures on food packaging bias serving size" explored four questions.
1. Do the calories of the foods pictured on fronts of packages exceed the calories stated on the package's per serving nutrition label?
Using cake mixes as an example the authors demonstrated that as pictured, with frosting, the slices of cake on the fronts of packages contained 134% more calories than the serving size calories published on the packages' nutritional facts panels.
2. Do people take extra ingredient calories into account when determining serving size?
Cornell undergrads were provided with two types of cake mix boxes and asked to estimate the "appropriate" number of calories per serving of cake.
One group of undergrads' boxes had photos of cake with frosting, while another group's boxes had photos of the same cakes unfrosted. The group with photos of cake with frosting were explicitly told that the frosting shown on the fronts of their packages' cakes was not included in the cake's back of box nutritional labeling. A third group was given boxes with photos of cake with frosting, but with no note regarding the frosting's calories not being included in the nutritional labelling.
The authors found that when there was no proviso about the frosting's calories not being included, the amount of calories that people believed were "appropriate" for a serving of cake rose dramatically.
3. Would clear front of package labelling about extra ingredients reduce serving size norms?
Using more undergrads, one group was provided with a box of cake mix that included a photo of cake with frosting and then asked to indicate what they thought would be a normal serving size, a second group was provided with boxes that included the frosting not included in calculations proviso, and the last group with boxes that included photos of frostingless cake. All groups used a series of cake slices that varied in size as determined by 100 calorie increments to make their selections.
The students who weren't told about the frosting, selected cake slices containing nearly double the calories of those told frosting calories were not included on the nutritional labelling.
4. Would labelling about extra ingredients reduce serving size norms in nutritionally savvy consumers?
Basically a repeat of question number 3, but with the participants being 44 food-service industry conference attendees.
With this group, despite being professional food service workers, when faced with the box without the proviso about frosting, though not nearly as significantly as with the undergrads, they too chose larger serving sizes.
Ultimately what this study suggests is that at least with cake, more accurate front of package food photography would influence how much consumers served themselves. The authors note that it is not at all uncommon for front of package food photos to include sauces, toppings and other supplemental extras that would not have been included in the product's labelling. There's also little doubt that in many (most?) cases, a boxed food's front of package photos are of servings much larger than the back panel's calculated serving size.
All of this to say that package reforms and legislative efforts need to consider more than just the nutrition facts panel, and that ensuring that front-of-package food photos accurately reflect both the panel's reported serving size, and that if there are extras, either they're accounted for on the panel, or a proviso is clearly provided stating that they're not, might influence that product's consumption.
[Reading the study my mind went immediately to cereal where serving sizes are usually in the neighbourhood of ½-¾ of a cup, and yet the bowls on fronts of boxes likely contain 2 cups or more.]