By Emily Reynolds

Going home from dinner out with a friend or a Sunday family lunch, you may notice you feel slightly more full than you normally do after eating. And while some of this may have to do with how many potatoes your mum insists you eat, new research seems to suggest that there could be something else going on. Researchers analysing dozens of past studies on the “social facilitation” of eating have confirmed that people do tend to eat more when eating in groups than alone — and have come up with several social and psychological mechanisms that could explain our increase in consumption in company.

Helen Ruddock at the University of Birmingham and colleagues embarked on a meta-analysis of 42 studies on the social facilitation of eating, including experimental research, where participants were observed eating alone and with others, and non-experimental studies, where participants recorded consumption in a food diary.

The review confirmed past findings, suggesting that we eat more when we’re with friends or family and are more likely to moderate the way we eat when we’re with people we don’t know. In that case, rather than pigging out, we choose smaller portions and eat less.

In studies using diary techniques, meal sizes were between 29% and 48% larger when eating with friends than when alone: one study found that an average of 23% more calories were consumed when eating in company. Three studies also found greater social facilitation effects for fatty and protein-rich foods.

The analysis also uncovered additional social factors that influenced how much people ate. Women tended to eat smaller portions in front of men, whether they were strangers or friends, and overweight people ate smaller portions in public for fear of being seen to overeat — one study found these groups would eat 18% less food when with others.

“People want to convey positive impressions to strangers,” explains Ruddock. “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.”

So why do we eat more when we’re with others? The team suggests it could be to do with the way our ancestors ate food, sharing it to protect against future food insecurity. Thousands of years on, many of us have no problem accessing food, but the mechanism remains.

Or as the team put it, 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.”

There are more obvious social factors, too: eating with others is, simply put, fun, and we therefore receive an “enhanced reward from social eating”, leading us to potentially over-consume. Overeating in company is also viewed less negatively than doing so alone, giving us permission to eat more with others. And if you’re a regular chef for friends and family, you’re likely to associate providing food with praise, giving you a self-esteem boost and strengthening relationships.

So next time you feel guilty about overindulging with friends? Fear not — you were simply strengthening your social bonds.

– A systematic review and meta-analysis of the social facilitation of eating

Emily Reynolds (@rey_z) is a staff writer at BPS Research Digest