Expert reveals how to burn the most calories while you are asleep

Staying in shape isn't easy. You can try all the fad diets and extreme workouts you like, but - ultimately - maintaining a healthy body and lifestyle takes constant work.

And we really mean constant.

Though you may not realise it, your body is always burning calories - whether you're sitting at your desk in the office, or kicking back with a cup of tea of an evening, or even when you're all tucked up in bed, asleep.

In fact, sleeping "correctly" is one of the best ways to ensure that you're burning a significant amount of calories during your downtime, and there are certain things you can do in order to get the most out of your nightly snoozes.

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Dr. Michael Breus, a sleep specialist, recently spoke to INSIDER about the most effective ways to burn calories while snoozing, and gave some helpful tips on how to ensure maximum calorie use during the night.

The first thing to do is ensure that you are getting a healthy amount of sleep: somewhere between seven and nine hours is usually what is recommended for most adults. "There's a tremendous amount of evidence that shows that if you're not sleeping both from a quality and a quantity standpoint you will gain weight," said Dr. Breus.

Sleeping for the correct amount of time will allow your body to enter a healthy amount of REM (Rapid Eye Movement) sleep - the stage "when we burn the most glucose [because] our brains are the most active."

"The longer you sleep, the more REM sleep you get, so you will burn more calories if you sleep longer," Breus reports - but that doesn't mean you can just sleep for days at a time and nap yourself thin.

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If you don't sleep enough, you'll most likely eat more the next day to take in the energy you need to say awake. However, if you oversleep, you may end up storing calories for the opposite reason. "Those who sleep too long have slower metabolisms because they stay in bed instead of expending energy," Breus explains.

Of course, it's quite difficult to determine the perfect amount of sleep, as everyone needs a different amount of shut-eye in order to function properly. By the same token, it's also tricky to work out how many calories are burned during the night, as it all depends on various factors including a person's age, weight, fitness, and need for sleep.

There is a rough way of working out how much you'll burn, however. According to fitday.com:

"Normally, a person burns about 0.42 calories for every pound in one hour of sleep. For instance, a 150 lb. person burns about 63 calories in one hour. If this person sleeps for eight hours total, he/she burns 504 calories for the whole duration. Just multiply the average rate with every pound of weight and number of hours of sleep.

"Therefore, the heavier a person is, as well as the longer a person sleeps, the more calories are burned."

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Some other important things to bear in mind are how late you eat your meals and how often you consume alcohol at night. Eating just before bed means your body does not have the chance to metabolise your food before you sleep, and drinking late will have the same effect - so give yourself three hours between a meal/drink and your bedtime.

Exercising late can also disrupt your sleep, as it energises the body and can make a person too warm to sleep comfortably.

Basically, then, the best way to burn the most calories at night is to try to get about eight hours of shut-eye, avoid eating, exercising, and drinking too late at night, and try not to oversleep if possible. Do all these things, and it could just be the extra little boost you need to stay in shape.