Friends don't let friends eat cookies: effects of restrictive eating norms on consumption among friends.

Social norms are thought to be a strong influence over eating, but this hypothesis has only been experimentally tested with groups of strangers, and correlational studies using actual friends lack important controls. We manipulate an eating norm in the laboratory and explore its influence within established friendships. In two studies we randomly assigned groups of three friends to a restrictive norm condition, in which two of the friends were secretly instructed to restrict their intake of appetizing foods, or a control condition, in which the friends were not instructed to restrict their eating. The third friend's consumption was measured while eating with the other two friends and while eating alone. In both studies, participants consumed less food when eating with friends who had been given restricting instructions compared to those who had not been given those instructions. In Study 2, participants who ate with restricting friends also continued to restrict their eating when alone. Experimentally manipulating social norms within established friendships is possible, and these norms can influence consumption in those social groups and carry over into non-social eating situations. These findings may suggest mechanisms through which eating behaviors may spread through social networks, as well as an environmental factor that may be amenable to change.