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New research from the Mayo Clinic, Minnesota, in which volunteers were overfed for two months, showed that the people who piled on the pounds did a lot less fidgeting than those whose weight stayed stable.
The scientist claim that encouraging fidgeting through "behavioural cues, may be a fruitful approach to the prevention of obesity".
Expert doubtful
However, Dr Eric Ravussin, Head of Obesity Research at Eli Lilly and Company, Indianapolis, told BBC News Online: "The study has been very well conducted but the extrapolation to everyday life is another matter. We have found this activity is a very strong familial trait so it is very likely to be genetically determined.
"I doubt there is any possibility of acting on this component of energy expenditure regarding the prevention of obesity."
But even if the facility to fidget is simply a fortunate genetic quirk in some people, it is certainly effective.
The 16 volunteers were fed 1000 calories a day more than they would usually need to keep their weight constant. Then they used modern laboratory equipment to track exactly what happened to the extra food.
"The originality of this study was to use state-of-the-art methods to assess all the different components of energy balance," says Dr Ravussin. "In that sense, the study was a "tour de force".
Fidgeting burns fat
On average 40% of the extra calories was piled on as fat, 33% burned off by subconscious fidgeting activities like shifting position in a chair. The rest was used in basic metabolic functions such as digesting the food.
However, while some volunteers put on only 360 grammes (13 ounces) in the two months, others grew heavier by as much as 4.2kg (9 pounds). The food eaten and exercise performed by the volunteers was carefully monitored, but this could not explain why the weight gains varied so much.
Key factor
The key factor, said Dr James Levine, the lead author of the study published in Science, was non-exercise activity thermogenesis (Neat) or fidgeting. "Those people who had the greatest increase in Neat gained the least fat, and vice versa.
Dr Michael Jensen also contributed to the study and noted: "When people overeat, Neat switches on in some people to "waste" this excess energy. Conversely, the failure to switch this on allows calories to be stored as fat".
Finally Dr Ravussin notes that it is ironic that storing extra energy as fat, rather than burning it off by fidgeting, would have been a great advantage during the famines or early humankind. "Today, however, it would be neat to understand just why some of us have more Neat than others."
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