Here's how your body uses calories while you're asleep

Mmm, sleep. The sweet slumber that rewards us at the end of every long day. It may not feel like you’re doing much with your eyes closed and your mind at rest, but your body is still hard at work on many basic functions.

Researchers are starting to piece together the puzzle of sleep — like why we do it, how much sleep we need, and how to sleep better. Another big question that is slowly being answered is the connection between sleep and weight loss.

We know that our bodies do burn calories while asleep. We also know that sleep deprivation has been linked to weight gain. But, there’s a lot more to the picture than that.

We’re unpacking the latest research on some of the key mysteries of sleep, namely, does sleeping burn calories? If so, how many calories do you burn while asleep? And how can this impact your weight loss journey?

What factors impact your energy expenditure while sleeping? 

Before we talk about how many calories you can burn while sleeping, we need to unpack why you’re burning calories at all. There are 3 main ways that your body uses energy:

1. Your resting metabolic rate (RMR)
2. Eating and digestion
3. Physical activity

Your RMR accounts for up to 80% of daily energy use. Eating and digestion make up 5-10%, with physical activity filling out the rest [8].

Physical activity can be anything from regular exercise (like walking, running or cycling) to incidental movement (like housework or walking to the train station).

You can see that by far the biggest contributor is your resting metabolism. That’s because even when your body is at rest, it requires energy to function properly.

You could be sitting at your desk, reading a book, watching TV or even sleeping and your body will still burn calories [3].

You may also have heard of basal metabolic rate (BMR) [4][8]. While RMR and BMR are similar, they are measured differently. For time spent at rest or sleeping, RMR is most accurate. 

Understanding your resting metabolic rate

Calorie burning while at rest might sound like a dream come true, but let’s not get ahead of ourselves. You burn fewer calories while at rest than you would while exercising, so you still need to focus on healthy habits like daily activity.

One review of multiple studies found that the average person had a resting metabolic rate of 0.8 calories per kilogram, per hour [3].

However, the review also found that RMR was higher in normal weight groups than it was in overweight or obese groups.

To put it another way, have you ever had a friend who could put away food like crazy but rarely put on weight? They most likely have a high metabolism.

Then there are other people with a slower metabolism, which makes weight management more difficult even with healthy habits. 

There are ways to influence metabolism from increasing your muscle mass to medical treatments.

One option is Pilot’s Metabolic Reset Program which combines clinically-proven treatments with health coaching to help you lose weight and keep it off, plus a supportive community of like-minded men on the journey with you.

How many calories do you burn from sleeping?

Let’s cut right to the chase — most people burn around 40-55 calories per hour while they sleep [6]. Over a full night's rest (~7 hours) that is equal to 280-385 total calories burned.

This might sound like a lot, but your energy expenditure is actually at its lowest while asleep. This is due to lots of reasons; like changes in your body temperature and the lack of activity required to stay comfy in bed [1].

This number is also just a rough idea, based on the average RMR. To get an exact number, you would need to know your individual RMR, which can be measured with the help of a health professional.

Lots of factors have a hand to play in your RMR, such as [6]:

• Your age
• Your gender
• Your muscle-to-fat ratio
• Certain health conditions that can affect your metabolism

Which sleep stage burns the most calories?

With innovations in sleep-tracking technology, we are now much more informed when it comes to what happens during those hours of shuteye.

One of the big discoveries was that sleep is not one long, unconscious state. Rather, it is happening in 4 stages. The first 3 sleep stages are known as non-rapid eye movement or NREM. The fourth and final stage is rapid eye movement or REM [1].

Here is what’s happening in each of the 4 sleep stages [2]:

• Stage 1 is when you start falling asleep as your heart rate slows and body temperature decreases
• Stage 2 is light sleep where you lose awareness of your surroundings
• Stage 3 is deep sleep which is the most important stage for restoring the body
• Stage 4 is REM sleep which is where you experience dreams

All 4 stages together make up 1 sleep cycle, lasting between 90-120 minutes. Each night, you experience multiple sleep cycles. The number of cycles depends on your sleep duration.

Throughout these sleep cycles, your metabolism fluctuates too. It is most active in stage 1 when you are falling asleep. It declines slowly over the night and experiences a slight uptick around 1 or 2 hours before you wake up [4].

Overall, your metabolism is consistently lower while sleeping. Overnight it reaches about 90% of your regular metabolic rate while awake.

The importance of deep sleep

In an interesting twist, the least active stage of sleep is actually the most important stage.

Stage 3, which is known as deep sleep, has an important role to play in repairing your body and helping you maintain a healthy body weight. Researchers also refer to this stage as slow wave sleep or delta wave sleep [2].

During deep sleep, your body releases 2 hormones: growth hormone (GH) and growth hormone releasing hormone (GHRH).

Both of these have a part to play in the repair and regeneration of your body, fat burning, and bone building. 

If you have an imbalance of GH and GHRH, you may struggle to burn fat and repair muscles which in turn, often leads to weight gain [2].

One of the ways to ensure you’re getting enough sleep for recovery is going to bed earlier. Yes, even if you're a night owl.

This is because your body releases the most GH and GHRH before midnight, which means an early night can play a big role in your overall health and losing weight.

For some people, getting enough deep sleep sounds more like a dream. It’s estimated that 1 in 3 Aussie men have trouble sleeping. This could be due to stress or sleep disorders like insomnia, sleep apnoea, and restless leg syndrome.

If a restful night’s sleep is constantly escaping you, Pilot’s Sleep Treatment may be able to help.

How to increase your energy expenditure during sleep

We’ve learned a lot so far about burning calories while asleep, so let’s take a moment to recap:

• Yes, your body does burn calories while asleep
• The number of calories is based on your resting metabolic rate
• People in a normal weight range typically have a higher metabolism than those who are overweight or obese
• People with more muscle mass typically have a higher metabolism too
• There are 4 stages to sleep with the most important being deep sleep 

Next, let’s explore some of the ways that you can increase your RMR, which in turn can help increase the calories burned while asleep.

While each of these tips has the potential to impact calories burned while asleep, they may not move the needle far enough if your goal is weight loss. For this, you may wish to seek out sustainable weight loss support.

Get plenty of sleep

Even though the recommendations say 7-9 hours of sleep per night, the average person is getting only 6.8 hours [1].

This 6-hour sleep trend has a lot to do with modern lifestyles. If we compare to estimates from a century ago, people were averaging a solid 9 hours of sleep.

Even though you can rely on coffee to stay awake through the day, your metabolism also takes a hit from sleep loss. Research shows that people who sleep less have a lower resting metabolic rate overall [5].

Not only does sleep deprivation slow down your metabolism, but it can also make you eat more. You pack in the calories in a bid to boost your energy levels and stay awake. 

In good news, research has also found that you can reverse these effects with a good night’s sleep, aka recovery sleep.

There are plenty of simple tips for how to get a better night’s sleep, such as:

• Building a pre-bed routine
• Keeping a consistent sleep schedule
• Doing a relaxing activity like reading, stretching or a warm shower
• Limiting blue light exposure from TVs, phones, and other devices
• Waiting until you’re yawning before going to bed

Sleep in a cool room

According to science, the optimal fat-busting sleep temperature is a chilly 18°C.

One study found that men who slept for 1 month in a room at this temperature had a faster metabolism and more brown fat in their bodies [7].

Brown fat is the kind that your body uses for temperature regulation. In other words, the body burns brown fat when it needs to increase your core temperature.

The link here is sleeping in a cold room increases the need for brown fat to be burned so that your body can stay naturally warm and toasty.

The study also found that the changes could be reversed. After sleeping for 1 month in a warmer 27°C room, the participants’ metabolic rate went back down to normal. 

Build up your muscle mass

The links between muscle mass and metabolism are clear, with more than one source finding that the more muscle that you have, the more calories your body burns [3][6][8].

A combination of exercise and diet is a great way to increase your lean muscle mass. For example, eating plenty of protein and doing resistance training a couple of times a week.

Eat a healthy diet

Diet has a large role to play in both your metabolic rate and your quality of sleep.

First, there’s the fact that not eating enough can actually slow down your metabolism [8]. When you don't eat enough, the body focuses on conserving energy. One way to do this is by slowing down your metabolic rate.

So, even if you’re aiming to lose weight, having the right balance of calories and nutrients is key. For example, protein is an essential fuel for your body that actually helps increase your metabolism [10].

Since it’s harder for your body to break down and use protein, it takes more energy to do it. This typically leads to a higher metabolism. 

Second, there is the way that food can improve your quality of sleep. Certain foods that are high in fibre or contain the sleep hormone melatonin have been linked to better quality sleep. Examples include [9]: 

• Beans
• Oatmeal
• Fatty fish
• Dairy
• Berries

On the flip side, other foods have been linked to poor quality sleep. Eating a diet low in fruits, vegetables, and whole grains has been linked to a restless night’s sleep.

In particular, saturated fats have been shown to interrupt deep sleep and refined carbs (white bread and pasta, for example) are known to increase appetite which can make you wake up overnight.

Finally, keeping an eye on your alcohol intake can help too. Even though the sedative effects of alcohol help you fall asleep faster, it's been shown to disrupt sleep patterns leading to lower sleep quality.

Image credit: Adobe Stock