It’s often pointed out anecdotally that food portion sizes in the U.S. are larger than those in other countries, which could contribute to the country’s increasing obesity epidemic. Now a new study has shown that this and other social factors might actually contribute to the food choices made by everyone.

The study, published in the Journal of the Academy of Nutrition and Dietetics, shows that peer pressure is a significant influencer on human food choices. Researchers found that informing study participants of others’ eating choices could influence whether they chose to eat high- or low-calorie foods. Having others suggest that participants eat more also increase the amount of calories consumed.

“It appears that in some contexts, conforming to informational eating norms may be a way of reinforcing identity to a social group, which is in line with social identity theory,” said Eric Robinson, lead investigator on the study and a psychologist at the University of Liverpool. “By this social identity account, if a person’s sense of self is strongly guided by their identity as a member of their local community and that community is perceived to eat healthily, then that person would be hypothesized to eat healthily in order to maintain a consistent sense of social identity.”

The study’s authors found that these factors can influence eating habits even when people are eating alone. Social norms were found to alter the normal behavior of study participants, even when they did not believe their behavior was influenced in such a way or when they had no motivation to please others.

“The evidence reviewed here is consistent with the idea that eating behaviors can be transmitted socially,” said Robinson. “Taking these points into consideration, the findings of the present review may have implications for the development of more effective public health campaigns to promote ‘healthy eating.’ Policies or messages that normalize healthy eating habits or reduce the prevalence of beliefs that lots of people eat unhealthily may have beneficial effects on public health.”