People who endlessly fidget when watching television are much less likely to be overweight than those who immediately settle into a comfortable position.

Scientists from Germany and the US believe that many of us possess a fidget molecule in our genes, which causes us to adjust and readjust when others are happy to stay still.

While crossing and uncrossing legs may not seem like the most vigorous of workouts, researchers suggest that it contributes hugely to weight control, expending energy that is otherwise unexploited. If you are the kind of person who irritates your friends by jiggling and squirming in the cinema, therefore, it's fairly likely you've managed to keep yourself in relatively good shape.

Lead researcher Professor Mathias Treier believes that people who fidget are in fact benefiting from a gentle but prolonged exercise regime.

"We're spending energy by doing that - and this is of course one of the key factors in energy balance," he said.

"We sit at our computers and our feet are still moving, even when we work at the computer. Clearly people who have the more fidgeting phenotype are more protected against diet-induced obesity, for example, than people who are more calm."

This conclusion was reached after mice with the Bsx fidget gene were found to be healthier and leaner than other mice, even when they were all enjoying the same amount of exercise. Fidgeting, it seems, is the ultimate method of weight control.

In April, a separate study in the UK found that people with two copies of a newly-discovered "fat" version of a gene are 70 per cent more likely to be obese than those with no copies.

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