Eating a snack on the go does not fill you up as much as sitting down to a meal at a table, researchers have found.
Even when the calories are exactly the same, if people think of their food as a 'snack' they will eat 50 per cent more later on than if they think of it as a 'meal'.
Experts at the University of Surrey believe people mentally 'tick off' their three meals a day.
So when they sit down to eat one of those meals they do not need to eat again for a few hours, reported the Daily Mail.
But if they grab a snack and eat it standing up, they do not tick it off, and feel as though they still need to eat again.
Study leader Professor Jane Ogden, a health psychologist at Surrey, believes the food industry is fuelling the obesity crisis by marketing food as 'snacks' to take advantage of Britain's on-the-go culture.
Her research team, whose work is published in the Appetite medical journal, tested their theory on 80 women.
The participants were each given a pot of supermarket pasta to eat - they could choose either cheese and tomato or tuna and sweetcorn.
They were then either told it was a 'snack' or a 'meal' - and were either given the food in a plastic pot and told to eat it standing up with a plastic spoon, or were served it on a ceramic plate at a table with metal cutlery.
When they had finished the food, each participant was led into a second room to take part in a 'taste test' of various unhealthy foods - chocolate biscuits, hula hoops, M&Ms and mini cheddars.
The scientists found those who had eaten a 'snack' standing up went on to eat far more in the subsequent 'taste test' than those who had had a 'meal' sat at a table - even though they had initially consumed the same calories.
The 'snackers' later ate 50 per cent more total calories - and 100 per cent more chocolate M&Ms - than those who had eaten the pasta sitting down at a table.
Professor Ogden said: "It is to do with registering that you have eating. Knowing that you have eaten is a psychological process - you tick off the fact you have had a meal.
"If you just have a snack you do not register it in the same way."
She added: "With our lives getting busier increasing numbers of people are eating on the go and consuming foods that are labelled as 'snacks' to sustain them.
"The food industry is aware we are eating more on the go and they are labelling food as sacks - it is exacerbating the problem of weight gain."
She added: "We should call our food a meal and eat it as meal, helping make us more aware of what we are eating so that we don't overeat later on."
Experts are increasingly worried about Britain's obesity crisis.
Some 67 per cent of adult men and 57 per cent of adult women in Britain are overweight - well above the global average.
Of these, 24 per cent of British adults - 12 million people - are considered obese, a vast increase since 1980, when only 16 per cent were in this category.
Growing evidence suggests the demise of the family meal eaten at a dinner table, and the boom in sandwich chains and fast food restaurants, means we are increasingly snacking on the go.
A report by the Royal Society of Public Health published last year found British adults add an average 767 calories to their diet every week simply by snacking on the journey to and from work.
Much of this intake was due to people grabbing croissants and other snacks on their commute because they had missed breakfast, the report said.
Another report by the UK Government's Behavioural Insights Team, also published last year, came to similar conclusions.
It said: "We are now more obese and more likely to say that we are trying to lose weight, both of which drive misreporting. We snack and eat outside the home more, making consumption harder to track."