The 44% effect: de Castro’s discovery
In 1990, psychologist John de Castro at Georgia State University asked a simple question: does eating with others change how much we eat? He had participants keep detailed food diaries, recording what they ate, when, and crucially, with whom.
The results were striking. Meals eaten with other people were 44% larger than meals eaten alone. This wasn’t about restaurant portions or special occasions. It held true across breakfast, lunch, and dinner. At home and at restaurants. On weekdays and weekends.
44%more food consumed when eating with others compared to eating alone. This effect has been replicated in over 40 studies across multiple countries.
de Castro and Brewer’s 1992 meta-analysis confirmed the finding: the more people at the meal, the more everyone eats. The relationship was linear. Two people meant more consumption than one. Seven people meant more than four.
+28%with 1 other person
+44%with 4 other people
+76%with 7+ people
This is called social facilitation of eating. The presence of others doesn’t just influence what we eat. It fundamentally changes how much we eat. And at restaurants, where meals are priced per item, eating more means spending more.
Source: de Castro, Journal of Personality and Social Psychology, 1990; de Castro & Brewer, Physiology & Behavior, 1992