The authors conducted their study in an Italian restaurant by using two sizes of forks to manipulate bite sizes and found that diners who used large forks ate less than those with small forks.
The authors then began to investigate why this finding seems to contradict earlier research on portion sizes. "We observe that diners visit the restaurant with a well-defined goal of satiating their hunger and because of this well-defined goal they are willing to invest effort and resources to satiate their hunger goal," the authors write.
In less flowery prose, people go to restaurants to eat. Reasonable enough.
Diners satisfy their hunger by choosing, eating, and paying for their food, all of which involve varying degree of effort.
"The fork size provided the diners with a means to observe their goal progress," write authors Arul Mishra, Himanshu Mishra, and Tamara M. Masters of the University of Utah, Salt Lake City. "The physiological feedback of feeling full or the satiation signal comes with a time lag. In its absence diners focus on the visual cue of whether they are making any dent on the food on their plate to assess goal progress."
The authors tested this conclusion by varying the quantities of food. They found that when the initial quantity of food was more (a well-loaded plate) diners with small forks ate significantly more than those with large forks. When customers were served small servings, the fork size did not affect the amount of food. Interestingly, in a lab experiment the authors found that participants with small forks consumed less than those with large forks. The authors believe that the participants did not have the same goals of satiating hunger as the restaurant customers did.
To avoid overeating, the authors suggest consumers learn to better understand hunger cues. "People do not have clear internal cues about the appropriate quantity to consume," the authors write. "They allow external cues, such as fork size, to determine the amount they should consume."