As the holiday season gears up, beware the popular tip that advises dieters to eat only half the food on the plate. According to a new study from University of Georgia marketing professor Julio Sevilla, that advice can play tricks on your brain — and your waistline.
Sevilla’s research, published in the Journal of Marketing Research, shows that the shape of objects can fool our brains. When we see an “incomplete” portion of food, like half a sandwich or a snack-sized candy bar, we tend to believe that it’s less caloric despite its actual nutritional value.
This can lead people to over-consume when their portions look incomplete.
“It is true that eating two pizza slices will satiate you more than eating one. However, there are many non-physiological factors that influence how full we feel, one being how much we feel like we’re consuming,” Sevilla said. “For example, people may mindlessly eat the broken pieces of pretzels or chips at the bottom of a bag, and feel justified that they haven’t had very much because they haven’t consumed any whole units.”
When people assume that “incomplete” portions contain less food than “full” portions regardless of their relative size, well-intentioned dieting advice can backfire and give consumers a reason to justify overeating, Sevilla said.
To examine how this affects consumers, he and co-author Barbara Kahn of the University of Pennsylvania ran an experiment offering cups of chocolate to two groups. One group was given cups containing full squares of chocolate while another was given cups with the same amount of chocolate broken into half-shaped pieces. Individuals who received the incomplete chocolate pieces ate more chocolate pieces than the other group.
Individuals in the experiments performed by UGA marketing professor Julio Sevilla showed a clear preference for the container without the handle, saying they thought it contained more product, even though both bottles contain the same amount.
“Just as most consumers trying to acquire or consume as much of a good as possible would choose completely shaped items, people attempting to consume less would usually prefer incompletely shaped products simply because they would perceive them as smaller and would believe they are consuming less,” Sevilla said.
In another experiment, medical professionals were given only the option of half-sandwiches at a luncheon, they ate more food in total than when complete-shape same size sandwiches were offered.
This type of bias carries over into the grocery store, where consumers are often influenced by a product’s shape, Sevilla said. Just as with food, when other products are sold in containers that seem “incomplete” such as having a hole for a handle (see Figure 1), consumers perceive them as containing less product regardless of the net weight.
“People rely heavily on visual cues and tend to disregard objective information such as actual serving size and the number of calories such serving contains, even when this is readily available on the product label,” Sevilla said.
So what can weight-conscious consumers do to ensure that “incomplete” products don’t sabotage their efforts?
Consumers assume that cheese with holes in it is "less complete" and therefore less caloric than an un-holed slice.
“One tip to take away from this research would be for consumers to not conclude automatically that incompletely shaped items are smaller, and instead to find out more about their actual quantity and caloric information, as firms sometimes offer such formats to lead consumers to ‘justified’ indulgence—that is, to make them believe they are consuming less when indeed they are consuming more,” Sevilla said. “Moreover, not all consumers are knowledgeable enough to effectively interpret this information. One way to mitigate the occurrence would be to try to make caloric information even more prominent on product labels and to promote nutritional education among consumers.”
He added: “Why I like to study satiation and the environmental cues that affect consumption is because we need to learn more about what factors affect product experience and satisfaction once we have decided what to buy. Moreover, while this work is relevant to marketing, it also has public policy implications, and teaching consumers about the consumption biases from which we suffer on a regular basis may have a positive impact on their health and wellbeing.”