Parents are failing to put enough fruit and veg into their children's packed lunches, health experts have warned.
The School Food Trust, which examined 3,500 packed lunches in England in 2009, says about 40% of lunchboxes do not contain any fruit or vegetables, compared with 10% of school dinners.
It said parents should consider switching to school meals.
Meanwhile, the World Cancer Research Fund has set up a website to give parents advice on healthier lunchboxes.
It says the same sort of changes as those made when TV chef Jamie Oliver championed school dinners are now needed.
It wants parents to ensure their children's packed lunches always contain at least two portions of fruits and vegetables.
WCRF head of education Kate Mendoza said: "There is no doubt Jamie Oliver helped achieve great things for the food served in school canteens. But as the nutritional content of school canteen meals has improved, the healthiness of the content of lunchboxes has been left behind.
"It is disappointing that children are going to school with lunchboxes that are not playing their part in helping to encourage the kind of healthy diet that is so important for their future.
"This is why we want to get across the message to parents that including a piece of fruit or using a portion of salad as a filling for a sandwich are positive things they can do for their children's health.
"It can sometimes be difficult for parents to control what their children eat, particularly if they are passing shops on the way home from school or visiting their friends. But parents can influence what is in their packed lunches and the fact that not all of them are doing so is a missed opportunity."
She said they were aiming to advise parents about healthy options - rather than telling them what not to put in as has happened in the past.
Patricia Mucavele, research and nutrition manager at the School Food Trust, which offers its own advice on packed lunches, said, "School lunches are now the most nutritious choice for children and young people.
"Packed lunches aren't as nutritious as school meals - they are typically higher in saturated fat, sugar and salt, and often contain foods that can't be provided in schools, such as sweets and salted snacks.
"Making healthy packed lunches that give children the variety they need in their diet takes a lot of time and effort.
"We have previously estimated that parents could spend almost eight days a year making packed lunches that meet the national standards for school food.
"And when you look at how the prices compare, it gives parents wanting to give their children good food, and save time and money, something to think about."
The trust's 2009 Primary School Food Survey, included an in-depth look at the contents of almost 3,500 packed lunches across 135 schools in England.
It found 58% of those with packed lunches had items that could count towards their "five a day" fruit and vegetable target, compared with over 90% of those eating school meals.