New research shows that having a bigger plate of food or being served larger portions makes us eat more.
In a review of 60 studies, scientists from the University of Cambridge found that portion size has a big effect on the amount of calories you consume.
The more food people were given, the more they ate - regardless of whether they had demonstrated good self-control in the past.
Researchers say their work helps to challenge common misconceptions that lack of self-control is why people overeat.
Gareth Hollands, from the behaviour and health research unit at Cambridge, said: "It may seem obvious that the larger the portion size, the more people eat, but until this systematic review the evidence for this effect has been fragmented, so the overall picture has, until now, been unclear.
"There has also been a tendency to portray personal characteristics, like being overweight or a lack of self-control, as the main reason that people overeat.
"In fact, the situation is far more complex. Our findings highlight the important role of environmental influences on food consumption."
He added that helping people to avoid "over-serving" themselves or others is likely to be an effective way of reducing overeating on a wider scale.
The idea of shrinking your plate to cut down on calories and lose weight isn't a new one.
The 'Small Plate Movement' encourages consumers to reduce the size of their dinner plates from the average 12" plate to a smaller, 10" plate.
Advocates of the movement believe that people who adopt this approach can lose 18lbs by changing plates.