Wolfing down meals may be enough to nearly double a person's risk of being overweight, Japanese research suggests.
Osaka University scientists looked at the eating habits of 3,000 people and reported their findings in the British Medical Journal.
Problems in signalling systems which tell the body when to stop eating may be partly responsible, said a UK nutrition expert.
He said deliberately slowing down at mealtimes might impact on weight.
The latest study looked at the relationship between eating speed, feelings of "fullness" and being overweight.
Just under half of the 3,000 volunteers told researchers they tended to eat quickly.
Compared with those who did not eat quickly, fast-eating men were 84% more likely to be overweight, and women were just over twice as likely.
Those, who, in addition to wolfing down their meals, tended to eat until they felt full, were more than three times more likely to be overweight.
Professor Ian McDonald, from the University of Nottingham, said that there were a number of reasons why eating fast could be bad for your weight.
He said it could interfere with a signalling system which tells your brain to stop eating because your stomach is swelling up.
He said: "If you eat quickly you basically fill your stomach before your gastric feedback has a chance to start developing - you can overfill the thing."
He said that rushing meals was a behaviour that might have been learned in infancy, and could be reversed, although this might not be easy.
"The old wives' tale about chewing everything 20 times might be true - if you did take a bit more time eating, it could have an impact."
In an accompanying editorial, Australian researchers Dr Elizabeth Denney-Wilson and Dr Karen Campbell, said that a mechanism that helps make us fat today may, until relatively recently, have been an evolutionary advantage, helping us grab more food when resources were scarce.
They said that, if possible, children should be encouraged to eat slowly, and allowed to stop when they felt full up at mealtimes.
Dr Jason Halford, Director of the Kissileff Human Ingestive Behaviour Laboratory at the University of Liverpool, said that the way we eat was slowly being seen as a key area in obesity research, especially since the publication of studies highlighting a genetic variant linked to "feelings of fullness".
His own work, recently published in the Journal of Psychopharmacology, found that anti-obesity drug sibutramine worked by slowing down the rate at which obese patients ate.
He said: "What the Japanese research shows is that individual differences in eating behaviour underlie over-consumption of food and are linked to obesity.
"Other research has found evidence of this in childhood, suggesting that it could be inherited or learned at a very early age."
He said that there was no evidence yet that trying to slow down mealtimes for children would have an impact on future obesity rates.