How Sleep Quality Affects Body Fat

Getting enough sleep and the quality of this sleep is so important for multiple health reasons. Lack of sleep negatively affects cognitive ability and your ability to physically recover from injury or illness. But did you know, losing sleep could increase body fat? 

Research suggests that there is a connection between sleep and your metabolism. In adults, sleeping for four hours a night, compared with 10 hours, increases hunger and appetite. This is especially true for calorie-dense foods that are high in carbohydrates. Have you ever suffered a bad night’s sleep and then really craved carbs the next day? Yep, there’s a scientific reason for that! 

Observational studies have also found correlations between sleep restriction and weight gain, which follows a similar pattern in children and teenagers. 




There was a study that found that a well-rested individual burns more body fat. Melatonin is not only crucial for sleep function but also for fat loss. Melatonin helps the body increase the mobilisation of brown adipose tissue – it’s brown because it has more mitochondria, making the tissue extremely energy dense, which is ideal for fat burning. 

We know that mitochondria are the energy power plants of the cells that create energy through ATP. So, this brown adipose tissue puts you in a metabolic advantage. 

Since the body produces melatonin exclusively in darkness, the more time spent in bed asleep means the more melatonin produced and therefore high mobilisation of brown adipose tissue. 


Leptin is the body’s hormone which makes you feel satiated, production of this hormone is boosted during, you guessed it, sleep! So, when adequate amounts of leptin is produced you will feel more satiated and also more in control of cravings. 

When your levels of leptin drop, you’ll have more issues with surrendering to food cravings and you will feel hungrier. What do you do when you feel hungrier and less in control of cravings? You eat more than your body requires.

Just one night of insufficient sleep can cause your leptin levels to go down. Therefore, if you have a poor sleep routine and/or are regularly not getting enough sleep, your leptin levels will be too low and therefore your desire for more food increases. Over time, this will contribute significantly to weight gain. 



When you sleep less, your cortisol levels start to rise. Your body doesn’t know, on a physiological level, why you’re not sleeping and, as a result, it believes you’re in danger. When your body perceives threat, you go into ‘fight or flight’ mode which releases cortisol and adrenaline. During this response, your body starts breaking down glycogen from the liver throughout a process called gluconeogenesis. 

Additionally, the increase of cortisol and adrenaline in your body will actually make it harder for you to sleep. Therefore, when you get into a bad sleep routine, you find it harder to fall asleep easily and a more reasonable time. You may also find yourself having more restless sleeps. It is important to try and break these bad sleep habits because, not only will you physically feel the effects of sleep deprivation, but you may also see the effects in weight gain! 


It will be unsurprising to you that lack of sleep results in feeling tired. Feeling fatigued is inevitably a contributing factor to weight gain, as when you are overtired you will not feel like overexerting yourself, resulting in less physical activity and, as a result, burning less calories. 

So, in short, losing sleep means eating more and exercising less. If this becomes a regular state, I don’t need to tell you what that means for your body weight!  

When you do feel fatigued because of a bad night’s sleep, the best thing you can do is physical activity. Exercise will make you feel more awake short term and should aid your sleep the next night. If you are physically tired, you are more likely to fall asleep easier and quickly break a potential poor sleep routine before it properly becomes a bad habit! 



If you didn’t have enough reasons already, avoiding unwanted weight gain is another reason to get a good night’s sleep! 

Even if you are trying to gain weight, I suggest you do this in a healthy way. This is the same for losing weight. You need your body to be functioning properly to avoid health issues, which often have knock-on effects to your body fat and ability to gain or lose weight. 

Healthy and functioning bodily systems mean that you can make the changes you desire, or maintain a happy and healthy weight, on your terms! 

If you are struggling with sleep, you may be facing some hormone imbalances which are affecting your ability to fall or stay asleep. There are multiple root causes to poor sleep but the best place to start is by running a Cortisol Test. This at-home saliva test will look at your cortisol production at four different times of the day. There is nothing better than this when it comes to getting an accurate picture of what your diurnal rhythm looks like.

If you are putting on or losing weight without trying, there may be more going on under the surface. An Organic Acid Test or Stool test can highlight if you are suffering from any gut or digestive issues which may be contributing to this. 

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