The Delboeuf Illusion. A serving of pasta appears smaller than it really is in the middle of a large plate, while the same serving of pasta appears larger than it really is on a smaller plate.
A large white plate of fettuccini Alfredo pasta sits on a crisp, black tablecloth.
A smaller white plate of spaghetti Bolognese sits next to it.
Which plate looks like it has more pasta? Which plate actually has more pasta?
It may sound trivial, but this is one important perceptual brainteaser.
New research suggests color – the color of the plate and even the color of the tablecloth – affects how much people serve themselves. It is difficult for people to visualize what a serving size looks like, said Debbi Beauvais, a nutritionist and spokeswoman for the American Dietetic Association. “Size of plate definitely plays into portion size.”
Part of the problem is the average size of a dinner plate has increased 30 percent since the 1960s, according to Brian Wansink, a professor of applied economics and management, and director of the Cornell University Food and Brand Lab.
After an initial study confirmed people overserved themselves on large plates and underserved themselves on small plates, Wansink, and Koert van Ittersum, a professor of marketing at Georgia Tech, decided to further explore the behavioral effects on food consumption.
Wansink and van Ittersum’s most recent study suggests plate and tablecloth color are two additional elements related to serving size.
Their study was based on the Delboeuf illusion, the idea that the perceived size of a circle depends on the size of the circle that surrounds it.
“When the inner circle is sufficiently smaller than the outer circle, it appears smaller than it actually is,” explained Satoru Suzuki, an associate professor of psychology at Northwestern University. “When the inner circle is sufficiently similar in size to the outer circle, it appears larger than it actually is.”
Discovered by a Belgian philosopher in the late 1800s, the Delboeuf illusion is common in psychology literature, but van Ittersum said it had never been used to explain food-serving behavior.
Wansink and van Ittersum studied the effect of color-contrast between plates and tablecloths and between plates and food to determine how people view serving size.
They performed a two-tiered study, comparing high and low color contrasts with small and large plate sizes.
In high color contrast conditions of a white plate on a black tablecloth, the Delboeuf illusion was in full effect. People served more than the target serving size on large plates, and less than the target serving size on small plates.
In low color contrast conditions of a white plate on a white tablecloth, the Delboeuf illusion was more or less eliminated. People served very close to the target serving size for both large and small plates.
“If you have white plates, consider eating off of a white tablecloth,” van Ittersum said.
To examine the effect of color contrast between food and dinnerware, a large generic plate was used. Participants were divided into two groups – red sauce pasta and white sauce pasta. Each person was randomly assigned a red or white plate.
Participants who ate white pasta on a white plate or red pasta on a red plate, significantly overserved themselves, according to the study.
The study used an average serving size of about 114 grams. The low color-contrast group served themselves 74 more grams on average.
“When serving yourself on large plates that have a similar color to the food, the amount of overserving increases,” van Ittersum said. “Your brain has to work harder to figure out how much exactly to serve.”
Participants in high color-contrast conditions, red pasta on a white plate or white pasta on a red plate, served less than the low color-contrast conditions, but still ended up overserving themselves by 32 grams.
“Should the size of a plate or bowl encourage a person to eat only 50 more calories a day, the resulting mathematical increase in weight would be approximately five pounds each year,” van Ittersum said.
Beauvais recommends measuring serving sizes into dishware to get a visual idea of what a correct portion looks like. “Sometimes the best thing to do is change your dishware to fit the correct portion size,” she said.