Anyone who's left the family dinner table uncomfortably full may be all too familiar with this phenomenon, even if they can't exactly name it.

New research, published in The American Journal of Clinical Nutrition, suggests that eating more when you're surrounded by family and friends is related to a phenomenon called "social facilitation." The group of researchers from the University of Birmingham, led by Dr. Helen Ruddock, systematically reviewed more than 40 studies that used experimental and nonexperimental approaches to examine food intake.

The review confirmed the researcher's hypothesis: we eat more when we're with friends or family, but are also more likely to change the way we eat when we're with people we don't know. Past studies revealed that meal sizes were between 29% and 48% larger when eating with friends than when alone; however, myriad social factors came into play when gender, obesity and dining companion familiarity were involved.

"We found strong evidence that people eat more food when dining with friends and family than when alone," Ruddock said in a press release. "However, this social facilitation effect on eating was not observed across studies which had looked at food intake amongst people who were not well acquainted."

Our food intake is moderated when it comes to how well we know our co-eaters. Both women and obese people had the strongest reaction to eating in front of other people.

Women ate smaller portions in front of men, no matter if they were a friend or stranger, while overweight people tended to eat less when out in public — for fear of being viewed as gluttonous. One study showed that both groups ate 18% less food when in the company of others.

Says Ruddock, "People want to convey positive impressions to strangers. Selecting small portions may provide a means of doing so and this may be why the social facilitation of eating is less pronounced amongst groups of strangers."

Table for one

solitary man eats alone in restaurant. Social norms give us 'permission' to eat more when we're surrounded by friends and family. When we're alone, not so much. (Photo: Guian Bolisay [CC by SA 2.0]/Wikimedia Commons)

Food is a loaded subject, and both the restriction and overeating of it can bring about social stigma. If we fear others' judgment, we might restrict our actions. Anxiety about our appetites can also contribute to discrimination that leads to fat shaming and other harmful social practices.

"Findings from previous research suggest that we often choose what (and how much) to eat based on the type of impression that we want to convey about ourselves," adds Ruddock. "Evidence suggests that this may be particularly pronounced for women eating with men they wish to impress and for people with obesity who wish to avoid being judged for overeating."

The team of researchers believe that some of this behavior is almost instinctual, harkening back to our ancient ancestors' hunter-gatherer methods. Thousands of years ago, after securing a large harvest, people would share the food amongst each other as a way to strengthen social bonds and protect against potential food insecurity.

Says Ruddock, "What we describe as 'social facilitation' can be seen as a natural byproduct of social food sharing — a strategy that would have served a critical function in our ancestral environments. This also explains why it is more likely to occur in groups with individuals who are familiar with each other."

Today, most of us have no problem securing food daily, but the urge to hunker down and split an entire pizza with a friend may still exist. While the strengthening of social bonds is one positive outcome, the downside is that we're still eating more food than we should.

As stated in the study, the "recent and rapid transition to a dietary landscape in which food is abundant has created forms of evolutionary mismatch … in the case of social facilitation, we have inherited a mechanism that ensured equitable food distribution but which now exerts a powerful influence on unhealthy dietary intakes."

While we wait for our evolutionary adaptations to catch up to our stomachs, there are other common-sense explanations, too. Eating with others is a social act, a way to connect with others; it's even advocated for by public health officials, celebrity chefs and consumer marketing. It's no wonder that we receive an "enhanced reward from social eating," but feel shame if we do the same in private, by ourselves.

So the next time you sit down to a big family meal, perhaps shift your focus from how much of Grandma's mashed potatoes you can eat to how much quality time you're spending with family. There may not always be room for dessert, but surely there's always room for more socializing.

Lindsey Reynolds ( @https://twitter.com/LindseyKateR ) takes an epicurean and academic approach to foodways, but she also writes about so many other things, including art, psychology and how to live an environmentally responsible life.

Why do we eat more when we're with our friends and family?
It's not just that your mom encourages second helpings. Studies show that a phenomenon called "social facilitation" is one factor in why we overeat with others.