Research by Brian Wansink, a professor of marketing and nutritional science at the University of Illinois at Urbana-Champaign, challenges the conventional notion that a person's ability to control eating and stick to a successful diet has solely to do with willpower.
Little-understood contextual cues -- such as how food is displayed and its variety of colors -- can lead people to overindulge and unknowingly bulk up, he says in an article he wrote that has been published in the Journal of Consumer Research.
For example, adults offered six colored flavors of jellybeans mixed together in the same bowl ate 69 percent more than when the colors were each placed in separate bowls.
In another study, moviegoers given M&Ms in 10 colors ate 43 percent more than those offered the same number of M&Ms in seven colors. Wansink and co-author Barbara E. Kahn, a professor of marketing at the University of Pennsylvania, concluded that not just variety, but the perception of variety, stimulates how much a person consumes.
"People eat with their eyes, and their eyes trick their stomachs," Wansink said in an interview. "If we think there's more variety in a candy dish or on a buffet table, we will eat more. The more colors we see, the more we eat."
In the case of jellybeans, a variety of flavors in a bowl was greeted by such comments as "looks really colorful," "feels enjoyable," "satisfied as I ate" and "gives me at least one flavor that I like."
An earlier study by Wansink found that moviegoers given an extra-large bucket of popcorn will eat up to 50 percent more than those given a container one size smaller -- even when the popcorn is stale.
Other studies have found that, hungry or not, office employees will eat more if their desks are stocked with food, or if the food is nearby, or if the package is open, or if the container holding the food is clear rather than opaque.
"Many of us are reasonably diligent about what we eat, but we don't put that much thought into how much we eat," Wansink said. "People may decide to eat grapes instead of potato chips because it's healthier. Once they make that initial choice, they tend not to monitor how much they eat. And a pound of grapes isn't calorie-free."
Consumers need to become more aware of how color, package size, variety and physical proximity influence the amount of food they ingest.
"If we ate 100 fewer calories a day, instead of gaining 10 pounds at the end of a year, maybe we'd lose 10 pounds. Small factors, like the type of candy bowl in your office, might add five more Hershey's Kisses a day to your diet," he said.
"People may say: 'What's the big deal? Five more chocolates isn't that significant.' But five more chocolates is 125 more calories per day. Over a month of weekdays, that's 2,500 calories, or two-thirds of a pound."
Wansink, the director of the Food & Brand Lab at Illinois, offered several tips about ways to curb overeating:
- Avoid multiple bowls of the same food at parties or receptions because they increase perceptions of variety and stimulate overeating.
- At buffets and receptions avoid having more than two different foods on your plate at the same time.
Wansink's tips for mothers and food vendors to promote healthy eating include:
- Arrange foods into organized patterns and avoid cramming meal tables or restaurant display cases with too much variety.
- Arrange fruits and vegetables in less-organized patterns to stimulate appetites.
- Assemble smaller helpings of more items for children or elderly adults with finicky eating habits.
The title of the paper, which appeared in the March 2004 issue of the journal, is "The Influence of Assortment Structure on Perceived Variety and Consumption Quantities."