Getting less than five and a half hours of sleep a night could see you gain nearly a stone in a year, say scientists.

Scientists say that even if diet and exercise habits remained the same, the changes in the body’s metabolism can cause the pounds to pile on.

A team of researchers from Boston believes this could explain why people tend to become larger as they get older and often struggle to get enough sleep at night.

They also think it could explain why night shift workers who struggle to sleep during the day are more prone to being overweight.

The academics from Boston compared the effects of sleep on 21 volunteers over six weeks.

They started off having ten hours of sleep a night but this was then reduced to just over five and a half hours at any time during the day.

Getting less than five and a half hours of sleep a night could see you gain nearly a stone in a year

Often volunteers were attempting to doze off during the day time when their body clock was telling them that they should be up and about.

The researchers found that when the subjects were deprived of sleep their metabolism rate dropped by 12%.

This is energy needed to maintain the body’s normal functions such as the lungs breathing and heart beating.

If this rate comes down, less energy or calories will be used up so weight will be gained – even if exercise levels and diets are unchanged.

It was calculated that when the volunteers slept for less than five and a half hours they burned off 120 fewer calories that day.

Over the course of a year this would lead them to put on 12.5 pounds, just under a stone.

The researchers said this could explain why people who work at night are more likely to develop obesity and diabetes. Their body clock or “circadian rhythm” is disrupted so they are unable to sleep as well during the daytime and their metabolism slows down.

Dr. Orfeu Buxton, whose study is published in the journal Science Translational Medicine, said: “Since night workers often have a hard time sleeping during the day, they can face both circadian disruption working at night and insufficient sleep during the day.

“Getting enough sleep is important for health, and sleep should be at night for best effect.”