Sleep and weight loss. How does a lack of sleep affect body fat and muscles?

Do you exercise, stick to a diet and count calories, yet still aren’t seeing the weight-loss results you’d hoped for? Before you cut back on your meals or add another workout, take a look at how much time you’re spending on sleep.

Many people treat a night’s rest as the final item on their daily to-do list. First comes work, chores, training, home life, a bit of ‘me time’, and only then sleep. It often happens that the planned eight hours are reduced to five or six. The problem is that the body needs time to recover after a full day – including after physical exertion.

Sleep is important not only for our general well-being. It can affect our appetite, energy levels and body composition, and therefore also how weight reduction. Interestingly, it is possible to lose a similar number of kilograms whilst losing different amounts of body fat and muscle.

Sleep and weight loss – why doesn’t the number of kilograms tell the whole story?

During weight reduction The aim should not be solely to achieve a lower weight. It is also important to consider which tissues the body draws energy from. Our primary concern is to reduce body fat whilst preserving as much muscle mass as possible.

That is precisely why it is so important body recomposition, that is, a change in the ratio between adipose tissue and muscle mass. In practice, this means that weight loss alone is not always the best measure of progress.

This is confirmed by the findings of a study published in 2010 in the journal Annals of Internal Medicine. Researchers investigated how reducing the amount of time spent sleeping affects the results of a weight-loss diet.

The participants used the same nutrition plan, but they spent different amounts of time in bed: 8.5 or 5.5 hours. It is worth clarifying that this did not mean they actually slept for 8.5 or 5.5 hours. The average duration of actual sleep was approximately 7 hours and 25 minutes and 5 hours and 14 minutes, respectively.

In both groups, body weight decreased by around 3 kg. However, the difference lay in the composition of the weight lost.

Those who had more time to sleep lost an average of 1.4 kg of body fat. In the group with less time allocated to sleep, the loss was just 0.6 kg. When sleep was restricted, the majority of the weight lost came from lean body mass.

This is an important point for those who care about improving one’s figure, and not just on weight loss. However, the study was small – it involved 10 people and lasted 14 days. It should not be regarded as definitive proof of all the long-term effects of sleep deprivation. It does, however, show that the time spent resting may be important when trying to lose weight.

Lack of sleep, body fat and appetite

A short night It can make itself felt as early as the very next day. It becomes harder to concentrate, tiredness sets in more quickly, and your planned workout starts to seem less appealing. Some people also find their appetite changes – it’s easier to reach for an extra snack, something sweet or a larger portion of food.

A lack of sleep can affect the mechanisms that regulate hunger and satiety, as well as eating behaviour. If this happens regularly, it becomes more difficult to stick to a weight-loss diet.

It is worth remembering that obesity It is a complex health issue. It is not caused by a single factor; body weight is influenced by, amongst other things, diet, physical activity, genetic predisposition, hormonal balance and sleep quality.

That is why it is not worth reducing weight loss to nothing more than counting calories. A well-balanced diet, daily exercise and recovery should all go hand in hand.

Muscle recovery after a workout begins outside the gym

During strength training, the muscles are stimulated to adapt. The muscle fibres are subjected to stress, and the body triggers processes that enable them to adapt to the exertion. Over time, this can lead to increased strength and improved fitness.

However, this does not mean that the more training sessions you do, the better. Muscles need time to recover. It is important to get enough sleep, to rest between training sessions, and to follow a diet that provides energy and nutrients.

Protein is particularly important, as it provides amino acids which are used, amongst other things, for tissue repair. The other nutrients are equally important macronutrients, because carbohydrates and fats also play important roles in the body.

If you train regularly but don’t get enough sleep, you may feel more tired and find it difficult to maintain your current training intensity. In the long run, this may make it harder to stick to your training plan.

Does physical activity improve the quality of sleep?

The relationship also works the other way round. Regular exercise can help improve the quality of your sleep, and a good night’s sleep helps you recover after exercise.

A review of research on resistance training found improvements in selected sleep parameters among people who exercise regularly. The beneficial findings primarily concerned the subjective assessment of the quality of night-time rest.

This does not mean that every workout will automatically improve your sleep. What matters is regularity, the intensity of the exercise and how your body responds. For some people, very intense exercise carried out just before bedtime can make it harder to fall asleep.

It is best to find a balance of activity that allows you to train regularly without leading to constant exhaustion.

How many hours of sleep should you get whilst losing weight?

Most adults are advised to get at least 7 hours a day. However, there is no single ideal amount for everyone. Sleep requirements depend, amongst other things, on age, state of health, activity levels and individual predispositions.

It’s worth ensuring not only that you get enough sleep, but also that your sleep is regular. Simple habits can help:

• going to bed and getting up at roughly the same times;
• limiting the use of mobile phones and computers before bedtime;
• ensuring that the bedroom is dark, quiet and at a suitable temperature;
• avoiding heavy meals and alcohol immediately before going to bed;
• regular physical activity throughout the day.

If, despite getting enough sleep, you wake up feeling tired, often wake up during the night or snore loudly, you shouldn’t take this lightly. One possible cause is sleep apnoea, which causes recurrent breathing disturbances during sleep and can significantly impair the quality of sleep.

Don’t cut back on sleep if you want to lose weight effectively

During slimming It’s easy to focus on what’s visible: calorie counts, workouts and changes in body measurements. However, the results are also influenced by processes that we cannot observe directly.

Sleep helps the body cope with the stresses of everyday life, and a lack of sleep can make it harder to control your appetite, recover from exercise and maintain a regular routine.

You don’t have to get a perfect night’s sleep every night. Start by getting regular sleep and make sure that sleep isn’t the first thing you cut back on when you’re short of time.

If your aim is to fat reduction and to improve your figure, remember: diet and exercise are important, but your body also needs time to recover. Sometimes an extra hour’s sleep can be a better choice than another hour spent at the gym.

Sources:

1. Nedeltcheva A. V., Kilkus J. M., Imperial J., Schoeller D. A., Penev P. D. (2010). Insufficient Sleep Undermines Dietary Efforts to Reduce Adiposity. Annals of Internal Medicine, 153(7), 435–441.
https://pubmed.ncbi.nlm.nih.gov/20921542/

2. Stich F. M., Huwiler S., D’Hulst G., Lustenberger C. (2022). The Potential Role of Sleep in Promoting a Healthy Body Composition: Underlying Mechanisms Determining Muscle, Fat and Bone Mass and Their Association with Sleep.
https://pubmed.ncbi.nlm.nih.gov/34348331/

3. Xie W. et al. (2024). The Optimal Exercise Intervention for Sleep Quality in Adults: A Systematic Review and Network Meta-analysis.
https://pubmed.ncbi.nlm.nih.gov/38641082/

4. Dolezal B. A. et al. (2017). Interrelationship Between Sleep and Exercise: A Systematic Review. Advances in Preventive Medicine, 2017, 1364387.
https://pmc.ncbi.nlm.nih.gov/articles/PMC5385214/

5. D’Aurea C. V. R. et al. (2019). Effects of Resistance Exercise Training and Stretching on Chronic Insomnia. Brazilian Journal of Psychiatry, 41(1), 51–57.
https://pmc.ncbi.nlm.nih.gov/articles/PMC6781703/

Katarzyna Pawłowska – a journalist specialising in health and lifestyle topics. A graduate in Journalism from the University of Warsaw, she is passionate about creating expert content on health, beauty and longevity (the science of living longer).