If you want to lose weight the surprising answer is to stay in bed longer.
Those who are 'short sleepers' are more likely to end up overweight even if they are more active than 'long sleepers' during the day, according to new research.
Short sleepers tended to have greater difficulty getting to sleep and staying asleep.
Tests found suffering sleepless nights can disrupt natural hormonal balances. This can reduce levels of the 'hunger hormone' leptin, causing people to eat more.
Researchers in the US analysed the sleep activity and energy expenditure of 14 volunteer nurses at the Walter Reed Army Medical Centre in Washington DC.
Each participant wore an arm band that measured movement, temperature, body position and other indicators of activity and rest.
Those identified as 'short sleepers' had an average body mass index (BMI) of 28.3 - classed as overweight - compared with 24.5 - classed as normal - for 'long sleepers.'
This was despite the overweight individuals taking almost 25 per cent more steps and using up nearly 1,000 more calories per day.
Chief investigator Dr Arn Eliasson said: 'Primarily, we want to know what is driving the weight differences, and why sleep and weight appear to be connected.'
Stress may also play a role in both reducing the length and quality of sleep and increasing eating and other weight gain behaviours.
'Higher perceived stress may erode sleep,' said Dr Eliasson, who presented the findings at the American Thoracic Society's annual meeting.
'Stress and being less rested may cause these individuals to be less organised than normal weight individuals, meaning they would have to make more trips and take more steps to accomplish the same tasks. This might add to their stress and encourage other unhealthy behaviours like stress-eating.
'We are planning further studies to evaluate the role of stress in sleep and metabolism.'