Ice cream illusions: bowls, spoons, and self-served portion sizes

Picking out the perfect bowls and spoons sounds like a concern solely for brides-to-be, but a new study of eating habits suggests that selecting right-sized serving utensils may help dieters avoid unconscious overeating.

Using willing colleagues as guinea pigs, the researchers threw an ice cream social to test whether oversized bowls and extra-large ice-cream scoops caused partygoers to dish up more dessert.

"Just doubling the size of someone's bowl increased how much people took by 31 percent," said lead author Brian Wansink, a consumer researcher who studies the psychology of food choice. "We also saw that giving people a scoop that was a little bit larger increased things by about 14.5 percent," said Wansink, director of the Food and Brand Lab at Cornell University.

The study appears in the September issue of the American Journal of Preventive Medicine.

Eighty-five food and nutrition experts gathered at the ice cream social to celebrate a colleague's achievement. The researchers randomly handed out either 17-ounce or 34-ounce bowls, and provided either 2-ounce or 3-ounce serving scoops. The guests scooped out the ice cream themselves.

Diet experts and nutritionist have already documented a string of environmental clues that influence consumption. They include the variety of food, music, temperature and whether we're with someone who's eating faster or slower than we are, Wansink said. The visual illusion caused by tableware may be another environmental clue that affects food choice, he said.

"Four ounces of ice cream in a small bowl may appear an appropriate amount for a mid-afternoon snack, but the same in a larger bowl may appear too small, leading one to over-serve," the study said.

All but three of the partygoers finished all the ice cream they had put in their bowl.

Each bowl of ice cream was weighed before it was consumed, and each diner was asked to estimate how much ice cream and calories they had selected. Wansink said the study participants, who were mostly nutrition experts, judged the size and calorie-counts of their portions better than most Americans would. But that intellectual knowledge did not keep the professionals from taking more ice cream when they were given larger bowls and spoons, he said.

"The fact that even they end up being tripped up by these cues just helps to show how ubiquitous and how subversive these illusions can be," said Wansink.

Fast food restaurants are blamed for up-sizing the food they serve. But nutritionists say most Americans have unrealistic ideas about proper portion sizes, so many people pile on too much food when they serve themselves at home.

Nurse educator Luann Daggett said Wansink's study findings mesh with the advice she regularly gives her patients.

"That's certainly one of the primary hints that we give to clients engaged in weight control: ‘Don't use a giant dinner plate, use a smaller plate;' presumably you put less on it," said Daggett, an associate professor at William Carey College School of Nursing in Hattiesburg, Miss.

"Every little step you can take to decrease your intake and increase your exercise output helps to address the problem," Daggett said. But she added, "Overweight and obesity is such a complex problem, with so many factors that such a simple intervention like that is not going to be able to address the full scope of the problem."

Still, Wansink says a series of small changes can make a big difference. He urges people to re-engineer their environment to avoid overeating.

"We do know about people's willingness to lose weight the hard way, which is denying yourself," Wansink said. He added that simply decreasing how many calories they daily consume by 15 or 20 percent, "would result in, for most people, 30 pounds a year of weight loss."

"An easier way of helping yourself eat less, is to adjust your immediate environment - your kitchen, your dining room, your desk where you work," he said. Choosing smaller bowls and spoons may also help, he said.

The powerful illusion of flatware size also holds potential for people who do not eat enough, Wansink said.

"Often times, we look at these things through the lens of ‘How can I use this to eat less?,'" he said. "But there's a big set of people out there - whether they be the elderly, parents of fussy eaters or people who aren't healthy - where the big issue is ‘How do you get someone to actually eat more?'"

Wansink B, van Ittersum K, Painter JE. Ice cream illusions: bowls, spoons, and self-served portion sizes. Am J Prev Med 31(4), 2006.