A study recently published in the Journal of Consumer Research suggests that the company you keep can unconsciously affect how much you eat.
In summary, if you observe an overweight person eating a large meal, you are likely to eat less than if you observe a thin person eating a large meal.
“This indicates that people are influenced, even without being aware of it, by other people’s portion choices,” according to one of the authors. “Further, our dining companion’s body type can lead us to adjust what we choose and consume ourselves.”
You can see a short 3-minute interview with the authors here.