The influence of social factors on the eating behaviors of humans was investigated by paying 153 adults to maintain 7-day diaries of everything they ingested and the number of other people present. Over 3800 meals were separated according to the number of other people present at the meal. Meal size, macronutrient composition, and the deprivation ratio was found to increase while the satiety ratio decreased as a function of the number of people present in a fashion best described by a power function. Meal duration and the rate of intake were best described as linear functions of the number of people present. Meals eaten in large groups were over 75% larger than when eaten alone. The findings suggest that social facilitation of naturally occurring meal intake by humans is an extremely potent influence on intake that is an instance of a very general phenomenon governing many forms of behavior.