It’s already known that sedentary lifestyles, stress and lack of time to prepare healthy meals are causes of an obesity epidemic, particularly in developed countries. But studies are looking at other factors contributing to the problem – even down to the size of the dinner plate.
A recent study by Georgia Tech professor Koert Van Ittersum and Cornell University eating behavior expert Brian Wansink found that the size of meal plates plays a bigger role in obesity than initially thought.
The study, published by the University of Chicago, measures the effect on eating of an optical illusion known as the Delboeuf illusion. The concept was discovered by Belgian philosopher Joseph Delboeuf and refers to the illusion that involves equally sized circles, one surrounded by a separate concentric circle. The circle that is surrounded appears bigger when the outer circle is close, and smaller when it is distant.
Researchers adapted this optical illusion to food and tested it on students at Georgia Tech, who were asked to serve themselves an equal amount of soup in different-sized bowls. Despite being told how much to serve, those with bigger bowls helped themselves to bigger portions.
“The findings reported here empirically demonstrate that the Delboeuf illusion may explain why and how dinnerware size influences serving behavior,” the study notes. “For nearly 150 years, the Delboeuf illusion has been regarded as robust, but of little practical value. In the context of serving behavior, however, it takes on an undiscovered dimension of everyday importance.”
According to nutritionist Mae Moreno, “there is a link between portion size and the size of dinnerware. It has been demonstrated by scientists throughout the world that one of the causes of obesity in the developed world like the United States is the increase in portion sizes.”
The study also noted that the size of U.S.-manufactured plates has increased by almost 23 percent since 1900. And when researchers compared portion sizes to those eaten in the early 20th century, the difference was more than noticeable.
“We’re also seeing a population that’s less active,” Moreno said. “In 1900, there weren’t as many cars, elevators and escalators as there are today, and kids’ games didn’t involve pushing buttons in front of a television, but rather they were games that involved movement.”
Education also plays a role, she said. Better-informed people tend to serve themselves smaller portions of food.
“Education is the basis for everything; educating ourselves about portion size, labeling and physical activity will benefit the entire family. There aren’t really good or bad foods, just badly balanced diets,” Moreno added.
In a similar study on 68 Cornell students, pasta was served at a sit-down, family-style dinner in a medium-sized bowl for a group of four. In a different setting with different students, pasta was served in a larger bowl. Although there was enough pasta for four students in both bowls, students with the bigger bowl ate nearly double what students with the smaller bowl ate.
“Our results showed that portion sizes in the medium-sized bowl setting closely resemble an average portion size (about 177 grams of pasta per individual), but that participants in the large-sized bowl setting strongly deviated from this average portion size and increased their intake to more than 300 g. It seemed that a large bowl stimulates overconsumption of a dish, [and] a medium-sized bowl makes individuals eat less than they normally would,” the study notes.
“These findings again highlight the role that external cues play in food consumption and show the importance of considering serving bowl size in nutritional education.”