A new study led by an Indian origin researcher has found that Diners eat more if food is labelled as "small" - even if the meal is actually bigger.
For the test, researchers labelled same sized cookies either medium or large and asked people to eat as many as they liked.
They found that in a surprising act of self-delusion, the test subjects gorged on the biscuits that were labelled medium.
The scientists behind the study said that people are easily tricked as they trust the labels and not what they are eating.
Study author Aradhna Krishna from University of Michigan said that the research had huge implications, as the test findings could be applied to clothing and drinks as well.
The marketing professor said that fizzy drinks varied in size from restaurant to restaurant but if people stuck to a "medium" sized food they could be getting more than they wanted.
"Just because there's a different size label attached to the same actual quantity of food, people eat more," the Daily Mail quoted her, as saying.
"But also, think they've not eaten as much," she said.
She said that over the last 60 years a "large" size had become six times the portions of the past, leading to the rising rates of obesity.