Food for thought: The research showed people tended to overestimate their self-control. Photo: New York Times

People can be educated about the importance of eating sensible serving sizes - but their self-control will fly out the window the moment they are given a bulging plate of food.

Nearly 100 undergraduate psychology students were given either a 350-gram or 600-gram serving of pasta and while researchers expected students given more would eat more, they also thought those educated about portion control would eat less. They were wrong.

''People often say education is a solution to overeating,'' said Lenny Vartanian, an author of the University of NSW research. ''So we tested that idea and it turns out that education doesn't improve things.''

Participants placed in the ''education group'' were given a brochure about how external factors, such as mood, advertising and portion size, can contribute to overeating. Those placed in the ''mindfulness group'' were taught how to focus on internal sensations such as taste, hunger and satiety before they were offered the pasta.

''Neither of these brief exercises reduced the effects of portion size,'' said Dr Vartanian, a senior lecturer at the university's school of psychology. ''Overall, participants in the larger portion group consumed about a third more pasta - 69 grams - than those in the smaller portion group.''

The difference amounted to about 365 kilojoules.

The study, published in the Journal of Health Psychology, raises questions about the effectiveness of education campaigns to curb overeating and suggests policy changes may be needed instead.

''There is enough talk in the media about portion size and people should be familiar about that concept,'' Dr Vartanian said. ''But we also know people tend to overestimate their ability for self-control and think of themselves as more able to control themselves than the next person.''

Guidelines released this year placed greater emphasis on portion size control in recognition that people struggled with the amount they eat, said Barbara Eden, a senior Heart Foundation dietician.

''Making small changes in food reduction is a sustainable and effective way to cut portion size,'' she said.