A gene linked to obesity causes people to put on weight by keeping them hungry, scientists have learned.
Previous research had shown that the gene, known as FTO, was strongly associated with obesity. But it was not clear whether this was to do with appetite or burning calories.
The new study of 3,337 children shows that the gene's effects are due to a lack of normal appetite control.
Usually the act of eating "switches off" the appetite and creates a feeling of satiety or "fullness".
The FTO gene stops this happening, scientists at University College London found.
Children with two copies of a high-risk version of the gene were less likely to have their appetite suppressed by eating.
FTO is the first common obesity gene to be identified in Caucasian populations.
Adults with two copies of the gene are on average 3kg heavier than those without the gene.
People with a single copy are 1.5kg heavier.
The new findings are published in the Journal of Clinical Endocrinology Metabolism.
Walking an extra 45 minutes helps diabetics
Walking an extra 45 minutes a day helps diabetics control their blood sugar levels, experts said yesterday.
Researchers found that diabetics who walked at lunchtime or before or after work burnt about 20 per cent more fat than usual.
The exercise improved the way their muscles stored sugar and led to better control of their diabetes.
Dr Michael Trenell from Newcastle University said: "We found that people who walked for an extra 45 minutes a day became better at burning fat.
"Over a period of weeks, this helped control their blood glucose levels."