Why sleep is so important for weight loss and exercise

I’ve had Matthew Walker’s seminal book Why We Sleep on my reading list for months and I’ve finally got round to reading it. It’s an absolutely fascinating exploration of the wonders of sleep. Walker delves into the science of sleep in a clear and understandable way. He guides the reader through a complexity of topics including: why we need sleep; the benefits of sleep; types of sleep; why we dream and how to transform your sleep leading to a healthier and more enjoyable life. 

In this post I’m focusing on sleep and weight loss as well as how sleep impacts on exercise. 

But first a general summary of the importance of sleep

Walker says: 

Sleep is the single most effective thing we can do to reset our brain and body health each day

Matthew Walker, Why we Sleep

Astonishingly Walker reports that two thirds of people in developed nations are failing to get the recommended number of hours of sleep. After reading Why We Sleep it does seem baffling that the virtues of sleep are not more widely understood. The evidence is super clear how important sleep is for our wellbeing. It’s therefore surprising how sleep isn’t treated in the same way as other crucial wellbeing topics such as diet, weight loss, exercise and smoking. Hopefully things are starting to change. 

It’s not cool not to sleep 

Culturally we celebrate the virtues of not sleeping rather than the other way round. Sleeping equates to laziness. We admire people working non-stop and surviving on minimal sleep. We respect people doing all nighters and it’s deemed heroic to miss entire nights of sleep. As Walker shows, time and time again in his research, getting less than seven to eight hours sleep consistently over our lifetimes is absolutely detrimental to our health. 

Getting enough consistent sleep seems like such a simple solution and of course it isn’t for many people who perhaps have small children, sleep problems or health issues.

But I can function on less than 6 hours of sleep…

Walker says that a lot of people think they can function adequately on 6 hours of sleep, or less, but in reality they are damaging their minds and bodies:

Millions of individuals unwittingly spend years of their life in a sub-optimal state of psychological and physiological functioning, never maximising their potential of mind or body due to their blind persistence in sleeping too little.

Matthew Walker, Why we Sleep

He says only a very tiny fraction of people can actually function without negative consequences from this small amount of sleep. 

Benefits of getting enough sleep 

Consistently getting enough sleep (recommended 7-9 hours) has the most amazing overall health benefits. It…

• Extends the brain’s capacity for learning, consolidates memories and clears the mind of information we don’t need to retain so we can make new memories
• Allows us to make logical decisions and come up with solutions to problems (hence the term “sleep on it”) 
• Strengths and cements skills such as playing a musical instrument, performing martial arts or climbing 
• Heals emotional wounds
• Helps us to recognise emotions and facial expressions in others, therefore increasing empathy
• Regulates emotions and reduces angry outbursts 
• Reduces depressive and anxious thoughts and minimises risks of suicidal thinking 
• Helps to restore and repair our immune systems to protect against infection and sickness
• Protects against developing diseases such as Alzheimer’s disease, dementia and cancer
• Regulates appetite and helps to control body weight 
• Maintains a healthy microbiome in the gut 
• Improves our cardiovascular systems, lowers blood pressure and helps our hearts stay healthy. Even reducing the chances of having heart attacks.  
• Allows our bodies to exercise more efficiently and recover adequately.

There’s tonnes of fascinating research and insights in Walker’s book and I’d highly recommend you give it a read if you want to understand the benefits of sleep.

Sleep and weight loss 

I wanted to delve more deeply into the effects on weight loss and exercise in this post as Walker’s research is fascinating in this area. He states:

The less you sleep, the more you are likely to eat. Sleeping less than seven hours a night increases your probability of gaining weight, being overweight or obese, and significantly increases your likeihood of developing type 2 diabetes. 

Matthew Walker, Why we Sleep

The shorter your sleep the more you will eat and the more weight you will gain 

There are two important hormones involved in controlling appetite: leptin and ghrelin. Leptin provides a signal telling our minds we are full. Ghrelin does the opposite and produces a strong urge to eat. Scientific studies have clearly shown that inadequate sleep decreases levels of leptin and increases ghrelin. As a result, we are less likely to feel full and more likely to still feel hungry if we have had inadequate sleep. 

Walker discusses a seminal study by Dr Eve Van Cauter where two groups of participants were divided into those being allowed a) 8 hours sleep and b) four and a half hours sleep for four nights in a row. They were given access to the same food and took part in the same physical activities. 

The shorter sleeping group consumed 300 calories more each day totalling 1000 by the end of the experiment. Walker estimates this to be in the region of 70,000 additional calories in a year causing between 10 to 15 pounds of excess weight gain a year. 

Shorter sleep leads to cravings for more calorific foods

Other studies have shown that sleep deprived people are more likely to opt for more calorific food than those who sleep adequately. Van Cauter’s studies have shown that cravings for sugary food, carb rich foods and salty snacks like crisps all increase by 30-40% when sleep is reduced by just several hours a night.  

Lack of sleep and dieting 

If you are dieting and attempting to lose weight then sleep is crucial. Studies have shown that weight loss comes from different sources depending on how much sleep you get. A study was done with a group of dieters who were divided into groups. The first group were allowed a full night of sleep and the second group five and half hours over a two week period. 

Both groups lost weight but the group who had less sleep lost 70% of their weight from muscle and not fat. The group who had adequate sleep lost 50% of their weight from fat and preserved their muscle mass.

When not getting enough sleep the body becomes especially stingy about giving up fat. Instead, muscle mass is depleted while fat is retained. 

Matthew Walker, Why we Sleep

As Walker summarises: 

Short sleep will increase hunger and appetite, compromise impulse control within the brain, increase food consumption (especially of high-calorie foods), decrease feelings of food satisfaction after eating and prevent effective weight loss when dieting.

Matthew Walker, Why we Sleep

Sleep and exercise

Regular exercise has benefits for sleep. People who regularly exercise tend to enjoy deeper more sound sleep. Studies have shown that exercise frequently increases total sleep time and the time it takes to fall asleep is reduced. Sleep is also crucial for restoring muscles and repairing the body after exercise.

Research shows that bad sleep is detrimental to exercise performance:

When sleep was poor the night prior, exercise intensity and duration were far worse the following day. 

Matthew Walker, Why we Sleep

Sleep and exerCIse performance

Getting less than 8 hours sleep can have seriously detrimental effects on exercise performance.:

Obtain anything less than eight hours of sleep a night and, especially less than six, and the following happens: time to physical exhaustion drops by 10 to 30 percent and aerobic output is significantly reduced.

Matthew Walker, Why we Sleep

It also increases the risk of injury and has a detrimental effect on performance. In comparison when sleep is sound exercise performance is enhanced. Evidence is also clear that a sedentary lifestyle does not help with sleep. It’s a positive cycle: exercise will aid sleep and sleep will aid your fitness performance. It’s also true that the sleepier we are the less energy we have and are therefore more likely to be sedentary rather than doing exercise to burn additional calories. 

Walker notes that you should avoid exercise two hours before you go to bed. Exercise increases core body temperature which can make it difficult to fall asleep. 

Sleep and obesity

Based on evidence gathered over the past three decades, the epidemic of insufficient sleep is very likely a key contributor to the epidemic of obesity. 

Matthew Walker, Why we Sleep

So if you are trying to lose weight and shape up now is the time to start paying attention to how much sleep you are getting!  I’ll write about tips on how to ensure optimal sleep in a later blogpost.

Please leave this field empty

First name

Email *

Please subscribe to receive information about my next power ballad workouts, notifications on the latest blogposts and other news from Be Motivated Coaching.

We keep your data private and share your data only with third parties that make this service possible. See our Privacy Policy for more information.

Thank you for subsribing to receive updates from Be Motivated. Check your inbox or spam folder to confirm your subscription.