The late Dr. Irving Janis was one of the most distinguished social psychologists who ever lived. His innovative psychological theories, such as groupthink, have transformed the way people relate to one another. One of his most unique research experiments occurred on the Yale campus where he taught. Janis gathered together college students to analyze how the persuasiveness of a message could be enhanced. To some of the students he gave peanuts and Pepsi to snack on while listening to a persuasive appeal. Other students listened to the same message, but without receiving the peanuts or Pepsi. Janis then measured how the students responded to the message. The findings of his experiment, which were published in the Journal of Experimental Social Psychology, identified that the students who received the peanuts and Pepsi were significantly more persuaded by the message than those who had received nothing to eat or drink. Janis’ conclusion is consistent with the plethora of scientific studies that have proven that food intensifies receptiveness to a persuasive message. The question is why?
There are two scientific principles that answer this question. The first is that the good feelings associated with food have been proven to enhance one’s mood and boost the brain’s ability to comprehend information.  The positive emotional state that a tasty meal inspires naturally stimulates optimistic thoughts that enhance one’s receptiveness to a persuasive appeal.     
What’s more, numerous scientific studies published in the Journal of Personality and Social Psychology has verified that when people are in a positive emotional state they are less analytical and more likely to make rapid decisions.   Neuroscientist Antonio Damasio expounded on this reality when he affirmed that the emotional state influences the brain’s ability to construct a decision to such an extent that it will ultimately determine if a person chooses “one direction or another.”
Alice Isen, Professor of Psychology at Cornell University, has conducted in-depth research on how mood impacts perception. She writes that when people are in a good mood they perceive the world through rose colored glasses. For instance, Isen conducted a psychological experiment that illustrates how a positive state of mind boosts the brain’s ability to solve problems. For the experiment she randomly put participants into one of two groups. She showed the first group a television bloopers show and then presented those in the group with a challenging puzzle. However, the second group was only given the puzzle and did not view the television show. The results were that those who viewed the bloopers before receiving the puzzle were able to solve the puzzle faster than those who had not. The reason for the increased rate of creativity was that those who witnessed the bloopers were in a positive frame of mind. This upbeat mental state enhanced their ability to comprehend and think resourcefully, which enabled them to solve the puzzle at a faster pace than those who had not witnessed the comedic show.
Human beings are emotional creatures and it is crucial to remember that our moods influence our judgments. This is one of the reasons why food enhances persuasion. One prime example of the effect that food has on decision making is found in a study on judicial parole rulings. The peer-reviewed findings of this research were published in the prestigious Proceedings of the National Academy of Sciences. The study exposed that “judicial rulings can be swayed by extraneous variables that should have no bearing on legal decisions.” The research highlighted that when the judges made a ruling after a meal or snack they were six times more likely to grant parole than when ruling before a meal. This is because people intuitively link the positive feelings from food with the message they are presented with. This is why a delicious meal has the power to cause others to view what you are presenting in a more optimistic manner.
The second reason that food amplifies the persuasiveness of a message is because of a scientific principle called reciprocity. Reciprocity is a powerful social norm which affirms that you should repay others for what they have done to you. Sociologists have confirmed that this principle is a potent motivator across all human cultures.
The influence of reciprocity upon behavior was vividly demonstrated at an upscale Washington DC dinner party. In the midst of the party a man wielding a gun entered and demanded money from the guests. Surprisingly, while being robbed, one of the guests offered the thief some wine and cheese. This act of kindness prompted the robber to reciprocate by apologizing and promptly leaving the party without any of the guests’ money
There have been many psychological studies over the last 40 years that have proven that reciprocity increases receptivity to persuasive attempts.   One of the most famous scientific experiments on reciprocity was conducted by psychologist Dr. Dennis Regan. Regan found that if people were given an unsolicited gift of a bottle of Coca-Cola a few minutes before being asked to purchase raffle tickets those individuals purchased twice as many tickets in comparison to those who had been presented with the same invitation, but without the gift of a Coca-Cola.
Even non-profit organizations have seen the persuasive impact of reciprocity. For example, the American Disabled Veterans periodically sends out mailers requesting donations. The organization reports that when they send out a mailer the median response rate is 18%. However, if the mailer includes a gift, such as address labels, the response rate nearly doubles to an astounding 35%.
Even restaurant servers can leverage the influence of reciprocity to improve their tips. Research published in the Journal of Applied Social Psychology identified that when servers gave guests a piece of candy with the check, tips rose an average of 3.3%. Furthermore, the study also revealed that if the server gave each guest two pieces of candy the tip jumped up 14.1%.
Likewise, when you provide someone food you are leveraging the principle of reciprocity because even something as seemingly insignificant as a few pieces of candy, a soda or a bag of peanuts creates a debt that obligates the receiver to the giver. This psychological responsibility instinctively causes one to reciprocate by viewing the message of the giver in a more positive way.
In summary, science has proven that food does more than diminish hunger; it is also a tool that can amplify positive influence. This is why sales people offer potential customers snacks before beginning their presentations and top business executives regularly combine business meetings and meals. As respected social psychologist Dr. David G. Meyers confirms, “Those who like conducting business over sumptuous lunches with soft background music can celebrate those results.”
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 Ibid. p. 6889
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