School-based programs aimed at getting children to eat more fruits and vegetables were somewhat successful in a new review of the interventions - although kids were more likely to up their servings of fruit than vegetables.

On average, kids in the programs increased their daily fruit by one-quarter of a portion - about one-quarter of an apple or five raspberries - and increased vegetable consumption by less than one-tenth of a portion, or about half of a spear of asparagus.

It's not clear whether changes of that size have any health benefits, although fruits and vegetables are considered an important part of a healthy diet.

"We do know if children have good habits when they're younger they do tend to carry these through," said Charlotte Evans, a nutrition researcher at the University of Leeds in the UK, who led the new study.

"So a small improvement in fruits and (vegetables) could be very beneficial over decades, but ultimately we don't really know," she said.

Evans had designed her own intervention to help kids eat more fruits and vegetables, and wanted to see how well other programs had worked.

She and her colleagues gathered the published results of 21 school-based programs. Those varied from simple efforts, such as giving away free fruits and vegetables at school, to more intricate programs that changed the way foods were marketed at school and included home-based interventions.

All of the children involved - an average of 900 per study - were between five and 12 years old. The studies tracked their diets for up to two years.

Evans said the total increase in fruit and vegetable consumption for kids who participated in a school program, compared to those who didn't, was considered moderate.

Most of that increase came from kids eating more fruit, not vegetables - though the researchers could not determine why that was the case, they reported in The American Journal of Clinical Nutrition.

"Maybe during the school day it's easier to include fruit as a snack. To improve vegetable intake it might be more beneficial to target families at home," Evans told Reuters Health.

The U.S. Department of Agriculture recommends school-aged children eat one to one and a half cups of fruit per day - with one cup being roughly equal to an apple or banana.

Children should also eat one and a half to two and a half cups of vegetables each day, according to the USDA. One cup equals about two carrots or a large ear of corn.

The benefit of increasing daily servings slightly is not entirely clear. And the new review doesn't show whether kids' extra fruit and vegetable portions replaced less-healthy food.

"A potential unintended consequence of increasing fruits and vegetables is that they are added on top of everything else," said Gary Foster, director of the Center for Obesity Research and Education at Temple University in Philadelphia.

Foster, who was not involved in this study, said that given the problem of childhood obesity, programs might have more impact if they target obesity directly, rather than particular food groups.

"They need to get kids to be more active and to get kids to eat less. You have to say, 'substitute a banana instead of a candy bar,' instead of, 'eat more bananas,'" he told Reuters Health.

Evans agreed that the programs she reviewed are not a substitute for those that target obesity, but she believes they are still a worthwhile investment.

"Increasing fruits and vegetables is unlikely to have any major beneficial effect in treating obesity, but as part of having a healthy diet... it is part of the whole picture to prevent obesity," she said.