People are more likely to eat less if their dining companion consumes only a small amount of food, due to a psychological effect, a new study has found.
Researchers led by the University of New South Wales (UNSW) found that how much food your dining companion eats can have a big influence on how much you consume.
This psychological effect, known as social modelling, leads people to eat less than they normally would if alone when their companion consumes a small amount of food, researchers said.
Study lead author, Associate Professor Lenny Vartanian of the UNSW School of Psychology, said that in social situations the appropriate amount of food to eat can be unclear.
"Internal signals like hunger and feeling full can often be unreliable guides. In these situations people can look to the example of others to decide how much food they should consume," Vartanian said.
Vartanian and his colleagues analysed the results of 38 studies in which the amount of food that people ate in company was measured.
"The research shows that social factors are a powerful influence on consumption. When the companion eats very little, people suppress their food intake and eat less than they normally would if alone," he said.
"If the social model eats a large amount, people have the freedom to eat their normal intake, or even more if they want," he added.
The effect is observed in many different situations: with healthy and unhealthy snack foods, during meals, when the diner has been deprived of food, and among children, and it occurs independent of people's body weight, researchers said.
"It even occurs when the companion is not physically present and diners are simply given a written indication of what that other person ate," said Vartanian.
The effect appears to be stronger in women than men, and this may be because women tend to be more concerned about how they are viewed by others when they are eating.
The research also found that the modelling effect is stronger in older children than in younger children, which also suggests that relying on external rather than internal cues for how much to eat is a learnt behaviour.
The results are published in the journal Social Influence.