According to researchers from Georgia Institute of Technology and Cornell University, the bigger the dinnerware, the bigger the portion people will consume. People who use larger plates could end up serving 9 percent to 31 percent more than they actually would.
Research showed that since 1900, average size of dinner plates has increased by almost 23 percent. Eating only 50 more calories a day could raise the weight by 5 pound each year.
225 students participated in the study and were asked to pour a specified amount of tomato soup into 1 of 7 different sized bowls. Out of the 7 bowls, 3 were smaller, 3 were larger and 1 was the control bowl. Observations showed that less than the target serving size of soup was served into the smaller bowls and more was served into the larger bowls.
It was found in the follow-up experiments that even with education, awareness or practice, the bowl bias was nearly impossible to eliminate. People tended to over-serve in larger bowls up to 31 percent more than normal.
Such phenomenon might be explained by Delboeuf illusion, which is an optical illusion of relative size perception. People are likely to believe size of a circle is much smaller when surrounded by a large circle. When people place food onto a small plate, the serving size looks relatively larger than it is. This would lead people to underserve.
However, reduction of bowl bias is possible through changing color of tablecloth or plate. On average, people would reduce serving by 21 percent when color of plate was changed, and by 10 percent when color of tablecloth was changed.
In the presence of the perception biases, researchers concluded that the best solution is to replace larger dinnerware by smaller ones or contrast ones.