Yes, your body keeps burning calories while you sleep, but fewer than when you're awake. Better sleep won't make you thin. It'll make the diet more bearable. Don't turn a night's rest into yet another chance to count calories.
Calories and sleep in brief
You burn calories all night, though less than when awake. Energy use falls through the first half of the night, then levels off. Sleep stages make only a small difference. Staying up burns a little more across the day, but in a hospital study, people on short sleep ate more than they burned and put on weight. Aim for the 7 to 9 hours the NHS says adults need on average.
Your body keeps using energy all night, just less of it
The NHS says calories measure the energy in food and drink, which your body needs to work properly. It explains weight change as a balance: if you eat and drink more calories than you use, you're likely to put weight on because your body stores the extra as fat. Take in fewer and you're likely to lose weight as it uses stored fat.
As a guide, the NHS gives daily needs of 2,500kcal for an average man and 2,000kcal for an average woman.1 Treat those as guides rather than personal targets, because your needs vary with your age, weight and height, as well as how much exercise you do.
Sleep is when you use the least energy. Jung and colleagues measured energy use in seven young adults living in a whole-room calorimeter. They concluded that sleep conserves energy.2 It was a small lab study of young adults.
Your energy use falls through the first half of the night, then levels off
In Katayose and colleagues' study, 12 men slept until they woke naturally in the same kind of room. Their energy use fell through the first half of the night to its lowest point, a 35% drop, then stayed fairly steady until they woke.3 Because it was 12 men for one night each, it shows the pattern rather than your own numbers.
What happens to your energy use across a night's sleep?
- It stays level from lights out to waking
- It drops through the first half of the night, then stays roughly level
- It climbs steadily towards morning
In Katayose's lab the 12 men's energy use fell through the first half of the night to its lowest point, a 35% drop, then stayed fairly steady until they woke. One night each shows the pattern rather than your own numbers.
Staying up burns more, but short sleep made people eat more than they burned
Jung's seven volunteers used about 32% more energy overnight when kept awake than when asleep, and about 7% more over the first 24 hours without sleep. In a hospital study, Markwald and colleagues kept 16 adults short of sleep for five days, the length of a working week, and measured their energy use and eating.
Staying up burns a little more energy, but in a hospital study, people on short sleep ate more than they burned.
| One night kept awake | Five nights of short sleep |
|---|
| Who was studied | 7 healthy young adults (Jung, 2011) | 16 adults (Markwald, 2013) |
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| Extra energy used | About 32% more overnight | About 5% more per day |
|---|
| Eating | A fixed diet to keep weight steady | More than they needed, especially after dinner |
|---|
| Weight | Not reported | An average gain of 0.82kg |
|---|
The extra eating outstripped the extra energy burned. Going back to enough sleep reduced how much they ate, particularly fats and carbohydrates.4 With 16 adults and food freely available, the study shows a short-term effect. Don't mistake staying up for a diet.
Aim for the 7 to 9 hours the NHS says adults need
The NHS says everyone needs different amounts of sleep: adults need 7 to 9 hours on average, and you're probably not getting enough if you're constantly tired during the day.5 Seven to nine is an honest range, and that four-hours-a-night brag is a daft thing to be proud of.
How long did you sleep last night?
- Under the NHS average for adults. Five short nights in the hospital study led people to eat more than they burned.
- Within the NHS average for adults. If you still feel constantly tired during the day, you're probably not getting enough.
- Above the NHS average of 7 to 9 hours. Needs vary, so judge it by whether you're tired during the day.
A week of short nights adds up, so use our sleep debt calculator to estimate how much sleep you've missed.
Three calorie myths about sleep
Sleep advice gets needlessly complicated when every habit becomes a calorie-burning trick.
Myth: More REM sleep burns more calories.
Katayose found higher energy use in REM than in stage 2 and deep sleep, but the authors called these small fluctuations. Jung's team also saw only small differences between stages. Don't chase extra REM to burn calories, though our guide to REM sleep explains what happens during this stage if you're curious.
Myth: Food you eat late is stored as fat while you sleep.
The NHS explains fat storage through energy balance: eat and drink more calories than you use and the extra is stored as fat. The problem in the hospital study was how much people ate after short nights, so blaming the clock misses the point.
Myth: Burning calories in your sleep is a way to lose weight.
Your body is at its most economical asleep. The NHS says the more energy you spend on an activity, the more calories you use, so look to daytime activity for extra energy use rather than treating bedtime as exercise.
Exercise in the day and keep big meals and alcohol away from bedtime
These are the NHS's own sleep habits. To my mind, they're as close as sleep gets to helping with weight.
- some exercise during the day
- no exercise in the 4 hours before bed
- no big meal late at night
- no alcohol, tea or coffee in the 6 hours before bed
- up at your usual time
I'm sure exercise would help me sleep, but I don't do it. Alcohol wrecks my sleep and has me awake every hour.
Questions people ask about calories and sleep
There's no single figure, because your energy use depends on your size and how active you are, and your age plays a part too. Night is the low point of the day, and energy use in Katayose's lab fell by about a third at its lowest. Twelve men over one night can't give you a personal overnight figure, so treat any calorie calculator that offers one with suspicion.
Sleeping more won't make you lose weight on its own. Going back to enough sleep cut how much the hospital study's 16 adults ate, particularly fats and carbohydrates, but that was over days. Weight change still depends on the balance the NHS describes between the calories you take in and those you use. I see enough sleep as a way to make sensible eating less of a struggle, so don't treat extra hours in bed as a weight loss plan.
Yes, if you want to sleep well: the NHS lists a big meal late at night among the things to avoid when you can't sleep. Evening food was also where the extra eating showed up in the hospital study. Pay attention to that extra evening food if you're trying to manage your weight.
