"I could tell something was wrong with him as soon as he began eating solids as a baby. It was if the food was draining him," says Rita, 50, describing how her son Christoffer had yoyoed between passive and hyperactive behaviour until she had removed several staples from his diet including milk and grains.

Christoffer, today a normally developed 14-year-old, is one of 23 children suffering from hyperactive disorders who were put on milk-free diets in 1996-1997 and whose development has been tracked ever since by a small group of educators and researchers in the southwestern Norwegian town of Stavanger.

The group set out to prove a theory by Oslo-based scientist Karl Ludvig Reichelt that a metabolic disorder making it difficult to break down certain proteins, including casein (the protein in milk that makes it possible to make cheese), could cause mental problems like Attention Deficit Hyperactivity Disorder (ADHD).

"One of the kids I worked with started on the diet on Wednesday and by the weekend his parents said they saw a huge positive change in his behaviour," says special educator Magne Noedland, who helped spearhead the diet project.

All 23 children, who were between four and 11 years old when the project started, were suspected of having ADHD and had been shown to have abnormal levels of peptides in their urine.