A new diet and exercise plan to tackle childhood obesity pioneered by Great Ormond Street hospital has achieved a 97% success rate in significantly reducing children's weight.
On average children were 10% less overweight at the end of the 10-week programme, a joint project between the London children's hospital and the charity Weight Concern.
The hospital treated 34 children last year, of whom 33 lost weight. On average the children achieved a 10% reduction in their Body Mass Index (BMI), a measure of whether a person is within or outside of the normal weight range for their height.
The best result was a 27% reduction in BMI. One child increased their BMI by 2%.
A spokeswoman for Weight Concern said: "A 10% reduction in BMI over three months is a significant drop.
"Although we were disappointed that one child gained some weight, the results showed that those who lost the least attended the least therapy sessions.
The scheme, which finished in December, is based on a "traffic light" approach to food: red for crisps, chocolates and takeaways; amber for protein, carbohydrates and dairy products; and green for fruit and vegetables.
Red foods can only be eaten as treats once or twice a week, amber foods must be eaten in healthy portions, while green foods can be consumed freely, said Jane Wardle, professor of clinical psychology at University College London and honorary clinical director of Weight Concern.
Children and their families attended weekly therapy sessions where they received advice on diet and exercise. All members of the family were encouraged to eat healthily, be more active and support the overweight child. Calorie intake and exercise was monitored through their diaries.
Prof Wardle said involving the whole family in the treatment of childhood obesity produced better results.
She added: "The behavioural element of the programme is significant. There's a lot of emphasis on how to make changes to the child's diet and activity levels, and sustain those improvements, rather than simply recommending lifestyle changes. The children are set long and short-term goals, which helps them maintain weight loss.
"By getting them to monitor their diet and activity, they can record their achievements. We encourage parents to reward children for meeting weight loss targets, for example with a trip to the cinema."
Prof Wardle now hopes to carry out a three-year trial with 50-100 children, with the aim of convincing the NHS to roll the traffic light scheme out across the country.
Almost a third of all children are either overweight or obese, up 50% from the mid-1990s, according to the government's latest health survey for England.
The research, published in December, found that one in six boys under 15 is obese, a figure that has risen 60% since 1994, while 42% more girls, just under 17% in all, are obese compared with nine years ago.
