This breakthrough will offer a clue to schools baffled by the steep rise in the numbers of pupils diagnosed with dyslexia, dyspraxia, attention deficit hyperactivity disorder, and autism. Researchers now believe this is largely attributable to the lack of proper nutrition from conception onwards.
At least one experienced headteacher attending the conference said he had changed his mind about pupils after discovering the impact food can have on behaviour and learning. Mike Marshall, head of Greenwards primary in Elgin and former head in a disadvantaged community in Aberdeen, said he would look again at "difficult" pupils.
Addressing the conference on "diet, behaviour and the junk food generation", Michael Crawford, professor of brain chemistry and human nutrition at London Metropolitan University, said he had predicted the rapid growth of brain disorders 35 years ago.
He said it was clear that the rise of cardiovascular disease would be followed by problems with the brain because of continued poor diets and the failure of the food industry to focus on nutrition.
Brain disorders, such as depression and the learning difficulties faced in classrooms, are now the largest cause of ill-health in Britain, outstripping heart disease and cancer, the professor said.
Alex Richardson, a senior researcher at Oxford University, claimed up to a quarter of the school-age population had some form of learning impediment probably caused by the lack of the vital Omega-3 fatty acid in their parents' and grandparents' diets. Omega-3 is readily ingested through eating oily fish but is also available in dark green vegetables.
"There's the old folk tale that fish is good for the brain: it is," Dr Richardson said.
She believed there were clear overlaps between diet and conditions such as dyslexia and dyspraxia. Diagnosis often depended on which specialist was first introduced to the child.
"Ask any vet, who starts out with the same training as doctors, and their first line of treatment for physical or behavioural difficulty is nutrition. They know that it's to do with what you feed the animals," she said.
Dr Richardson is at the forefront of research on putting Omega-3 back into children's diets. Last May, she published her first findings from the Oxford-Durham study, an analysis of 117 underachieving primary children with motor difficulties in the Durham area who took part in a controlled six-month study.
Half the children were given fish oil supplements and half a placebo for three months; they then switched for a further three months. Both groups made the same "stunning" gains when they were on the supplements.
Dr Richardson said pupils would be expected to make three months' gains within three months but the supplements group made an average gain of nine months in reading and six months in spelling. "These kids are catching up with their peers when they started out two years behind," she said.
Most benefits were in attention span, and better behaviour among pupils with ADHD.
Professor Crawford appealed for all pupils to be given the skills and knowledge about food they need to make individual choices and described the removal of home economics from the curriculum - especially in England - as "one of the most naive decisions taken by government".
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