Secondary school pupils are not eating enough at lunchtime according to a study by the body overseeing school food.
Read the School Food Trust's full article here:
School Food Trust research suggests pupils get a quarter of the recommended daily intake from lunch, rather than the third that is advised.
A trust spokeswoman said it could be because pupils just chose a salad or a dessert rather than a full meal.
But there is evidence of significant improvements in school nutrition.
The School Food Trust report said: "The secondary school environment is more complex than primary, and the style of food service makes it more challenging to ensure that pupils are making healthy choices whilst catering for their needs at lunchtime."
The trust added in a statement: "The research shows that schools still need to do even more to encourage teenagers to fuel up well for their afternoon lessons.
"Despite huge improvements to what's on the menu, teenagers are still not choosing food combinations that will give them enough energy and nutrients to stay alert all afternoon."
It added that while the number of pupils eating fruit and vegetables every day had doubled since guidelines came into force, it still needed to go much further.
The report compared the eating habits of almost 12,000 pupils in 80 schools in England in 2011 with a smaller group of about 6,000 pupils in 2004.
'Sweets and crisps'
It found significant improvements in the nutritional value of meals offered by secondary schools and healthier choices made by pupils.
For example, in 2004 43% of pupils had chips with their lunch compared to just 7% in 2011.
And almost all schools have ditched the sale of chocolate, sweets and crisps.
Nutritional guidelines for school food were introduced in 2005 after a campaign by the TV chef Jamie Oliver exposed how unhealthy food was in some places. These were then strengthened and full guidelines came into force in 2009.
Senior nutritionist, Jo Nicholas, who led the research for the trust said: "These findings show that even just 12 to 18 months after the final standards came into effect, as many secondary schools were getting to grips with the changes, the legislation was already making a significant impact - not just for what was on the menu but also for what teenagers were actually eating.
"Instead of 'chips with everything' we're starting to see signs of 'chips now and again'," she added.