The idea of losing weight while you sleep may seem too good to be true for many dieters.
But, following a ground-breaking new scientific study, it could just be possible.
Researchers have discovered that sleeping in the cold can help you shed pounds because the body's metabolism speeds up to keep you warm.
The study suggests that people who sleep naked, under a thinner duvet, or who turn down their bedroom radiator could be reaping the rewards in terms of their weight.
Experts from the US National Institutes of Health asked male volunteers to sleep in climate-controlled bedrooms during the experiment, to see how their temperature affected their weight.
The research subjects were given identical meals to ensure they all took in the same amount of calories over the four-month period when the study took place.
They were also given the same sheets and night-clothes to make sure that did not affect the experiment.
The men then spent different months sleeping at different temperatures; one month at 18C, two months at 23C and one at 27C.
Scientists noticed that, during the week that the men slept at the lowest temperature, their bodies changed to enable them to lose weight.
Experts say the amount of 'brown fat', which produces heat by burning calories, doubled during the weeks at the cold temperatures, effectively speeding up the men's metabolisms.
When the men slept at the higher temperatures for a month, the effect went into reverse.
Francesco S. Celi, a professor at Virginia Commonwealth University, told the New York Times: 'These were all healthy young men to start with, but just by sleeping in a colder room, they gained metabolic advantages that could, over time, lessen their risk for diabetes and other metabolic problems. '
Brown fat, which produces 300 times more heat than any organ in the body and so burns off calories very quickly, is plentiful in babies but levels drop to almost zero as people become adults.
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