High calorie, low fibre Western diets are promoting hormonal imbalances in children which drive them to over-eat, researchers say.

Food manufacturers have created a "toxic" environment which dooms children to be overweight, according to Robert Lustig, a professor of paediatrics at the University of California, San Francisco.

In a review of obesity research, Professor Lustig said Western diets were causing children's bodies to over-produce insulin, creating an environment in which foods were "essentially addictive".

Changes to food processing in the past 30 years, particularly the addition of sugar to foods that never previously included it and the removal of fibre, both promote insulin production. "Fructose (too much) and fibre (not enough) appear to be cornerstones of the obesity epidemic through their effects on insulin," he said in a review published in Nature Clinical Practice Endocrinology and Metabolism.

Latest figures show one child in five is overweight and cases of adult-onset type 2 diabetes, linked with excess weight, are for the first time seen in children.

Professor Lustig said it had long been known that insulin acted on the brain to encourage eating by suppressing leptin, the hormone that signals fullness, and boosting the pleasurable dopamine rush that accompanies eating. Children could not be blamed for over-eating when the foods they were offered were "toxic" fast foods full of sugar and devoid of fibre.

"No child chooses to be obese. Young children are not responsible for food choices at school or home. It can hardly be said that pre-school children, in whom obesity is rampant, can be held personally responsible. If we don't fix this our children will continue to lose," he said.