Only 1% of primary school children's packed lunches meet the nutritional standards set for school meals in England, reveals research in the Journal of Epidemiology and Community Health.
On average, around half of UK school children eat a packed lunch brought from home, equating to 5.5 billion packed lunches eaten every year.
Prompted by concerns that school lunches were not providing sufficiently healthy food choices, new standards setting out the required healthy food groups for prepared meals came into force for all local authority schools in England in 2006.
These specify that school lunches must contain protein rich and low fat starchy foods, vegetables, fruit and dairy products. Meals cannot include sweets (confectionery), savoury snacks or artificially sweetened drinks.
These were followed in 2008 by further government standards on the energy, fat, salt, vitamin and nutrient content for school meals.
In the study, fewer than half of children's packed lunches met the government's 2008 nutrient standards, including levels of vitamin A, folate, iron and zinc.
On average, girls tended to be given, and eat more, healthy foodstuffs than boys, and children at schools with fewer pupils eligible for free school meals had healthier packed lunches.
The authors say their findings provide "evidence that the quality of food in children's packed lunches is poor ... Few lunches contained all five healthy food groups, but most lunches contained restricted foods and drinks such as crisps and cakes."
The new standards for school meals are producing "drastic improvements" in lunches provided by primary schools, but the same cannot be said for packed lunches, they add.