The otherwise innocuous pistachio shell is a great example of the counterintuitive way human beings consume food. While we think the amount of food we eat is driven primarily by hunger, that’s rarely the case. In reality, the amount of food we consume is usually dictated by the food environment around us.
For instance, research has repeatedly shown that we’ll eat more food regardless of how hungry we are if more food is put in front of us. And a study called “The Effect of Pistachio Shells As a Visual Cue In Reducing Caloric Consumption” demonstrates that simply seeing the remains of our food can have an impact on how much we’ll eat. Here’s how it worked:
The subjects were told they were going to evaluate a variety of brands of pistachios and were surveyed at the end of each day to determine their fullness and satisfaction. The subjects were offered pistachios on their desks for an 8-h period on two separate days and were able to consume the pistachios at their leisure during that time. Subjects began each day with a sixteen ounce bowl filled with four ounces of pistachios in the shell. They were also provided with a second sixteen ounce bowl, in which they were instructed to place the empty shells from the pistachios they consumed. Every 2 h throughout the day pistachios were added in two ounce increments. In condition one, the shells remained in the bowls until the end of the day, whereas in condition two, the shell bowls were emptied every 2 h throughout the day.
At the end of the day both groups reported being equally full and satisfied by their allotment of pistachios. However, the group that kept the empty shells in front of them ate 18 percent fewer pistachios than the other group. The study concluded that having a visual cue of how much they’d eaten (in the form of empty shells) is what made the difference.
This coincides with a similar study at Cornell University where two groups of people were given chicken wings to eat. For one group, the discarded bones from consumed wings were removed from the table right away, while in the other group the bones were left on the table in plain view. By the end of the meal the second group had eaten 27 percent fewer wings.
“The results suggest that people restrict their consumption when evidence of food consumed is available to signal how much food they have eaten,” said Brian Wansink, the John S. Dyson Professor of Marketing and of Applied Economics at Cornell.
In practical terms, you can apply the “pistachio effect” to other things as well. If you’re eating food that comes in a wrapper, don’t throw the empty wrappers away until after you’re done eating so they’ll help you keep track of how much you’ve eaten. At big social settings where there might be lots of hours d’oeuvre offerings, don’t clean your plate to make room for more goodies. And if you’re eating food buffet style, don’t get a fresh plate to go back for seconds. Keep your original plate with you to remind yourself of what you’ve already had. The result is that you’ll eat less but still feel satisfied.