Food buffet. (Photo: Sandratsky Dmitriy/Shutterstock)

Many factors influence our food choices. Our hunger level, of course. Any cravings we may be feeling. The extent to which our self-control has been depleted.

And then there’s the BMI of our dining companions.

In a newly published study, people lining up for lunch ate more of an unhealthy pasta dish if the first person in the queue appeared to be overweight.

This dynamic was found regardless of whether the person at the head of the line served herself a healthy or unhealthy meal.

“Both the body type and serving behavior of an eating companion may influence the quality and quantity of our food intake,” a research team led by Mitsuru Shimizu of Southern Illinois University-Edwardsville, writes in the journal Appetite. “The presence of an overweight eating companion may lead people to eat more unhealthy foods and, in some cases, less healthy foods.”

"Participants served and ate a significantly larger amount of unhealthy food when they saw an overweight eating companion than when they saw a normal-weight eating companion."

Shimizu and his colleagues, Katie Hancock and Brian Wansink of Cornell University, conducted the study in part because previous research suggests images of high-calorie foods or overweight people can influence diners in different ways.

According to one school of thought, they inspire excessive eating by temporarily dampening health-related goals. (“What’s the problem? I’m not as large as she is.”) But from another perspective, they could inspire healthy choices by reminding people of the unwanted stigma of being overweight.

In this new experiment, 83 undergraduates gathered in groups of 10 to 12 and served themselves a simple buffet lunch: spaghetti and meat sauce, and a salad. The first person in line was a female research associate, who made herself conspicuous by asking for instructions (“Do I need to use separate plates for pasta and salad?”) and deliberately dropping a fork.

For half of the lunches, this woman wore a “fat suit” that increased her perceived weight by 50 pounds, from a normal 126 pounds to an overweight 176 pounds.

In addition, at some lunches, she served herself a healthy meal (a lot of salad and a little pasta), while at others, she served herself a lot of pasta and a small salad.

After the participants served themselves and ate, the researchers measured how much of each dish they had consumed. They found the first person in line had a real influence on their choices.

“Participants served and ate a significantly larger amount of unhealthy food when they saw an overweight eating companion than when they saw a normal-weight eating companion,” Shimizu and his colleagues write.

Regardless of whether she served herself healthy or unhealthy portions, they report, “participants served and ate a larger amount of pasta when she was overweight than when she was normal weight.”

What’s more, participants ate less salad when that first woman appeared overweight and served herself a healthy meal (as opposed to when she appeared overweight and ate a lot of pasta). It's plausible that the image of her attempting to eat a healthy diet, but failing to lose weight, inspired a why-bother, I’ll-eat-what-I-want attitude.

In any event, the fear of stigma wasn't scaring anyone skinny.

These results clearly suggest the presence of overweight people in a food-service setting gives us license to indulge. So, even if you don’t go to the gym, you might want to lunch at the diner next door.