Packed lunches are an important part of children's diets

Two out of three children said they regularly discarded sandwiches, while one in three bin fruit.

However, they are more likely to eat crisps and biscuits - just one in five of those questioned said they would throw these away.

The findings are based on a survey of nine to 11 year olds at a school in Buckinghamshire by NOP for the manufacturers of Ribena Toothkind.

Parents' concerns

Researchers also questioned 262 parents from across the UK.

Two out of three said they were not concerned about whether or not their children discarded some of their lunch.

It seems many children are discarding elements of their lunch, which means they may be missing out on vital vitamins and minerals every day. Dr Wynnie Chan

Over 80% of children said they had thrown items away.

The parents were also asked if they thought their offspring consumed enough calories each day. Nine out of 10 parents said they did.

However, two out of three said they were worried that their children were not eating healthily.

Dr Ian Campbell, chairman of the National Obesity Forum, said he was not surprised by the findings.

"It typifies the situation at the moment that children have a generally unhealthy diet.

"It shows that it is not just the provision of healthy alternatives that is important - we need to create a situation where children will actually want to eat them."

Dr Campbell said peer pressure in schools had a lot to do with children not wanting to eat certain items in their lunch boxes.

"Even if children are given healthy snacks in their lunches they will sometimes not eat them because they fear they will be ridiculed by their friends."

Balanced diet

Family nutritionist Dr Wynnie Chan said the results of the survey should concern parents.

"It seems many children are discarding elements of their lunch, which means they may be missing out on vital vitamins and minerals every day.

"Parents meanwhile are blissfully unaware that their child is not receiving the balanced meal they've prepared.

"With children becoming more and more image conscious the problem is only going to get worse," Dr Chan said.

Amanda Wynne, of the British Dietetic Association, said it was important that lunch box foods were made as attractive as possible.

"The contents of lunch boxes are very important because getting good nutrition for youngsters will lead to better habits in later life.