Going out to dinner with your health-fanatic friend could help you make healthier food choices too.

A study found that when people went out to eat together and had to order their food out loud they tended to choose from the same category, a University of Illinois news release reported.

"My conclusion from the research is that people want to be different, but not that different," U of I food economist Brenna Ellison, said. "We want to fit in with the people we're dining with. It goes against the expectation that people will exhibit variety-seeking behavior; we don't want to be that different from others."

The researcher observed diners at a restaurant over a three month period. One section of the restaurant was the "control group," these customers were given a menu with only the name and the price of the food. The other group received a menu with calorie counts for every entrée. A third group got a menu with a calorie count along with a "traffic light" symbol.

"[A] green traffic light items contained 400 calories or less, yellow light items had between 401 and 800 calories, and red light items contained more than 800 calories," the news release reported.

The data for the study was based on information from customer receipts, but Ellison also went "undercover" to observe customers.

"I would help bus tables sometimes so that I could watch and make sure that the tables were getting the right menus," Ellison said. "Or I would send people in as 'secret eaters.' They could eat whatever they wanted. I just wanted to make sure that they got the right menu for that section."

Ellison stopped at the restaurant every day, and during that time she would speak to the staff.

"They said that people talked about the traffic lights a lot. And we did find that larger tables which received the traffic light menus did order fewer calories, on average, which suggests there was some peer pressure to order lower-calorie items," she said.

The data was also based on the customer's happiness and what their fellow diners ordered.

"The big takeaway from this research is that people were happier if they were making similar choices to those sitting around them," Ellison said. "If my peers are ordering higher-calorie items or spending more money, then I am also happier, or at least less unhappy, if I order higher-calorie foods and spend more money."

"The most interesting thing we found was that no matter how someone felt about the category originally, even if it was initially a source of unhappiness, such as the items in the salad category, this unhappiness was offset when others had ordered within the same category," Ellison said. "Given this finding, we thought it would almost be better to nudge people toward healthier friends than healthier foods."

The researcher would like do the experiment again, this time taking into account which customer at a table ordered first.

"Previous studies have shown that if you don't have to order audibly, everyone just gets what they want without any peer pressure involved," Ellison said. "Research suggests that you should always order first because the first person is the only one who truly gets what they want."