Encouraging children to eat fruit and vegetables is often a battle, but turning it into a competition could be the answer, according to research.

A new study suggests that playing to a youngster's competitive streak is likely to result in them choosing more of the healthy foods.

And it indicates that girls are more likely to respond to an element of competition in vegetable-eating than boys.

The study analyses the findings of a trial conducted by researchers at the universities of Bath, Edinburgh and Essex involving more than 600 pupils aged six to seven and nine to 10 in 31 English schools.

For the "individual" scheme, pupils were given a sticker if they chose a portion of fruit or vegetables at lunchtime, or brought one in as part of a packed lunch. They were given an extra reward if they picked, or brought in, more than four of the foods over the course of a week.

In the "competition" scheme, a second set of pupils were also given a sticker for choosing a portion of fruit and vegetables, but were split into groups of four, with the youngster in the group who had the most stickers at the end of the week gaining an extra reward.

There was also a control group that was offered no incentives for eating fruit or vegetables.

The researchers found that although the results differed by pupils' age, gender and background, overall offering pupils incentives increased their consumption of the foods, with the competition having a greater and longer-lasting effect than the individual scheme.

In the competition scheme, among those who were not eating fruit and vegetables every day before the trial, the proportion trying the foods increased by around a third, the study found.

It added that the individual scheme seemed to work very well for older children, but less so for younger pupils.

Dr Jonathan James, of the department of economics at Bath University, said: "Our study looked at ways in which we can better target interventions that change young people's eating habits in favour of them choosing and eating more fruit and vegetables.

"Through our research we found that introducing an element of competition at lunchtime could have larger effects on children's eating habits than using an incentive scheme that was based only on their own choices. By using a different approach, we found that the proportion of children trying fruit and vegetables could be increased by up to a third."

The study also found that boys responded to both the competition and individual schemes, while girls responded mainly to the competition.

Dr Patrick Nolen, of Essex University, said: "Interestingly, unlike in other work on competition, we find girls - rather than boys - respond more favourably to the competitive incentive. This means that girls, who generally eat more healthily than boys, increase their consumption of fruits and vegetables even more under our new incentive."

The findings are published just weeks after universal free meals were introduced for infant school children across England.

Under the move, all five to seven-year-olds are now eligible for a free school dinner at lunchtime.