Jeya Henry, a nutrition professor at Oxford Brookes university, said:
"There is a big push to tackle childhood obesity through schools, but children should not be castigated for eating 'good' or 'bad' foods.
"Eating disorders are increasing among children and we have to be careful about the messages we put across. Ignorance is widespread. Parents with overweight children need to be reassured. Many children are slightly chubby and that is fine. The correlation between chubbiness as a child under 10 and obesity in adulthood is only 10 per cent.
"The basic impediment for teachers is that they have no time and reliable information is not easily accessible.
"I have called on the Food Standards Agency and the Department for Education and Skills to collaborate in producing a systematised guidebook for all schools which is peer reviewed and neutral. I am told this would be expensive, but the cost of ignorance is tenfold."
Dr Dee Dawson, medical director of the Rhodes Farm Clinic, London, for young people with severe eating disorders, said: "I am unbelievably angry about nutrition teaching in schools. There is no reliable information but as many silly books out there as there are teachers to teach. People train for four years to be dieticians so why do we let untrained teachers loose on this? It has to be taught properly or not at all.
"I hear ridiculous things from my patients that they have been taught in school; that they shouldn't be drinking full-cream milk or eating beef or having butter on bread. In fact they shouldn't be eating low-fat anything.
A child's nutrient requirements are totally different to an adult's. A low-fat diet is no less than 30 per cent fat. We need fat daily to repair cell membranes. It is healthier to be 10 per cent overweight than 10 per cent underweight. How many know that?
"The children I see are the tip of the iceberg. So many thousands more develop compulsive obsessive behaviour around food that stays with them through life because of all this misinformation."
Help and advice is available from:l Eating Disorders Association: 0870 7703256; www.edauk.com; email firstname.lastname@example.org
* Ache (Anorexia in Children, Help and Encouragement): 01934 710336; www.anorexiabulimiacare.co.uk .