A new study has shown that people tend to underestimate how much of each item is present when faced with a large variety of items, so those on diet should better avoid buffets.
Joseph P. Redden of the University of Minnesota and Stephen J. Hoch of the University of Pennsylvania came to this conclusion after studying consumers' perceptions of quantity in a set of experiments.
Their aim was to determine how quantity perceptions influence portion sizes.
"Does a bowl with both red and blue candies seem to have more or less than a bowl with only one color candy?" the researchers asked.
"Contrary to popular belief, the presence of variety actually makes it seem like there are fewer items," they added.
The team first exposed participants to images of colored dots and geometric shapes.
"When items differ, people tend to focus on one type or the other, and find it difficult to merge the multiple types into a whole. However, a set composed of only identical items makes it easy for people to perceive the items as a single, unified whole," the authors wrote.
According to them, focusing on the larger whole makes a set appear to occupy more space.
"Since people rely on spatial area as a cue for quantity, a set appears to have more items when they are all identical," they said.
Having seen this perceptual effect in two studies with geometric shapes, the researchers decided to move on to food.
They asked some participants to pour food into containers, and observed them to pour more when the candy had a variety of colors.
"This occurs even though people knew they could not consume the candy. Specifically, people pour more in the presence of variety since they perceive lesser quantities," the authors add.
The researchers reckon that people's tendency to underestimate portions in the presence of variety may help better understand why they often eat more if there is greater variety in a meal.
"This misperception causes people to pour larger servings when there is variety, yet they don't realize they have done so. Since prior research has shown that people eat most of what they serve themselves, variety could lead people to eat more solely due to this perceptual influence," write the authors.
The team believe that understanding such visual tricks may help people get a handle on portion control, a key element in reducing obesity.
The study has been reported in the Journal of Consumer Research.