It's not just the company we keep that influences how much we eat. A new study suggests it's the sex of the people around us that leads us to consume more or less food.
Researchers from Indiana University of Pennsylvania and the University of Akron found that the average number of calories college students consumed varied depending on whether they ate with men, women or a mixed-sex group.
"What we found was that on average, when men were eating with women, they tended to purchase more calories than their counterparts who were eating with other men. Women tended to purchase fewer calories when with men as compared to when they're with women," said Marci Cottingham, a co-author of the study and a graduate student at the University of Akron.
The study's lead author, Molly Allen-O'Donnell, a graduate student at Indiana University, sat at an eatery on the Indiana campus during lunch and dinner times over a 10-day period. She observed what foods students bought and who their dining companions were.
"We observed them in a campus eating environment, during routine meals and just looked at the amount of calories purchased," said Cottingham.
The results, she explained, suggest that food strongly influences the impressions people form of each other. For White, college-age females, eating less is a way to seem more feminine when men are around, and for college-age males, eating more when around women is a way to appear more masculine. Men, whether unconsciously or consciously, don't want to be seen as light eaters, especially in front of women.
"The theory is you're more aware of gender when you're with the opposite gender and may want to prove your gender more," Cottingham said.
"In a mixed group, women may think they're being judged if they eat more calories," said Keith Ayoob, associate professor of pediatrics at the Albert Einstein College of Medicine in the Bronx, N.Y.
"It's also possible that women are eating more calories when they're with each other because they're more relaxed, or people may eat fewer calories in groups because they're enjoying the social aspects of the meal and aren't focused on eating," Ayoob said.
Alex McIntosh, a sociology professor at Texas A&M University in College Station, has done extensive research on eating behavior. He said it's a well-known idea that food helps form strong impressions of people in a variety of situations.
"I've had undergrads talk to me about eating on dates and in particular on the first day, if you're a female, some students reported even when given the opportunity to eat, they don't, and if they do, they eat far less than they ordinarily would because of the impression it makes," he said.
"Much attention has been given to the increase in obesity among both children and adults in the United States, as well as to eating disorders among young people, particularly women," the authors wrote. "Those who are trying to address these concerns should consider the importance of the role of gender and social context in developing solutions and meeting needs."
Because of the power of social relationships, they should be considered when educating the public about better nutrition.
"The impact of others is, of course, the logic behind nutrition education in schools, integrated into school meals and can offer opportunities in communities," said Connie Diekman, director of university nutrition at Washington University in St. Louis.
But giving people the nutritional information they need is also key, because even though people may eat less or eat healthier around certain groups of people, they may not make the same when they're alone.
"Restraining themselves when in a group doesn't mean that's all the food they're going to consume," said Ayoob. "People may eat very sparingly in a group and then hit the ice cream and chips at home."