Sleep: The Easiest Way to Muscle Growth and Fat Loss

Key Points:

Adequate sleep is essential for muscle growth, recovery, and anabolic hormone production.
Getting enough quality sleep makes it easier to maintain muscle on a diet.
Too little sleep impairs fat loss, makes it more challenging to get lean, and promotes hunger and overeating.
Most healthy adults need 7–9 hours of sleep, but you might need more if you’re serious about your training.
Sleep quality is as important as how many hours you sleep.

You will spend roughly one-third of your lifetime asleep. Not everyone needs the standard eight hours of Zs per night, but skimp out on your sleep for too long, and both your brain and body will know the consequences.

Sleep is essential not only for health and well-being but also for muscle growth and fat loss.

Your muscle mass is controlled by muscle protein synthesis (MPS) and muscle protein breakdown (MPB). Both happen simultaneously 24/7 and at the end of a typical day, most people’s MPS and MPB are about equal. Most healthy people who eat a balanced diet neither gain nor lose muscle.

Physical activity, including strength training, and nutrition are the two major factors controlling the size of your muscle mass.

In recent years, a number of studies suggest that lack of sleep might shift the balance between MPS and MPB to favor breakdown and the loss of muscle mass.

Conversely, getting plenty of quality sleep makes reaching your fitness goals, whether building muscle or losing fat, significantly easier. Research shows that poor sleep could make it easier to gain weight and body fat and cause you to lose more muscle and less fat on a diet.

Read on to find out how sleep affects your training and muscles and how to get the quality rest you need to optimize your body composition and performance.

The Importance of Sleep for Your Muscles

Plenty of neat things happen to your muscles when you sleep. Anabolic hormones, like testosterone and growth hormone, are released during sleep, and while muscle protein synthesis typically decreases during sleep, it’s a crucial time for muscle repair and recovery.

Growth Hormone

Growth hormone is crucial for growth, cell repair, and metabolism. It allows your body to grow and repair many of its tissues, including muscle. It also increases the breakdown of fat by helping release fatty acids that your body can use for energy.

The most substantial release of human growth hormone happens during the first sleep cycle of the night, which contains the highest proportion of so-called slow-wave sleep (SWS). It occurs within the first one to two hours after falling asleep and lasts an hour to 90 minutes.

During SWS, your body goes through the most potent restorative processes of the night. SWS is characterized by slow brain waves, relaxed muscles, and deep, restorative sleep.

Disruptions in your sleep, particularly in slow-wave sleep, can affect GH secretion, potentially impacting growth and metabolic functions.

Testosterone

Testosterone is the primary male sex hormone that promotes muscle growth by enhancing protein synthesis, increasing the number of satellite cells in muscles, and making the body more efficient at re-using broken down proteins to create new muscle proteins.

The secretion of testosterone is circadian, following a roughly 24-hour cycle. Over the course of the day, it responds to light and darkness. Your testosterone levels peak in the early morning and then decline throughout the day.

However, testosterone levels are also influenced by sleep, regardless of what time it is.

After you fall asleep, testosterone levels start to rise, plateauing after about 90 minutes when you enter REM (rapid eye movement) sleep. This happens if you fall asleep during the day as well, suggesting there is also a component to testosterone release directly related to sleep, not just time of day (or night). According to some research, testosterone levels in young men are mainly regulated by sleep, not the clock.¹

As little as one week of too little sleep (less than six hours per night) can lower your testosterone levels by up to 15% compared to getting eight hours.² Compare that number to a typical decrease in testosterone levels with age, 1–2% per year. This is 15% in one week. Many people, including athletes, bodybuilders, and lifters, get six hours or less of sleep on a regular basis.

Given testosterone’s powerful effects on your muscle mass, it’s safe to say that you want to get enough sleep to keep it as high and healthy as possible.

Cortisol

Cortisol is a stress hormone secreted during physiological and psychological stress. Like testosterone, cortisol levels typically peak during the early morning hours before declining during the day.

While short bursts of cortisol release, like after a weight training session, are a healthy and natural part of building muscle and nothing to worry about, constantly elevated levels inhibit muscle growth and increase muscle breakdown.¹

Sleep is closely related to cortisol release. Not sleeping enough leads to higher cortisol levels. But it’s not all about how much you sleep. Your sleep quality also matters. Even if you sleep enough hours, a night of poor sleep keeps cortisol levels elevated for longer during the day.

Inflammation

Inflammation can be both good and bad for your muscles.

Acute inflammation, like after a workout, is essential for gaining muscle mass. Taking large doses of NSAIDs (anti-inflammatory pain medicines) after training prevents your muscle protein synthesis from elevating above everyday levels.

However, chronic inflammation is bad for just about everything, including your muscles. Sleep is also associated with inflammation in several ways.¹

Firstly, research shows that inadequate sleep increases inflammation levels in the body. To date, no studies look at the long-term effects of increased inflammation due to poor sleep on muscle mass and growth, but an association would not be surprising.
Secondly, chronic inflammation can contribute to insomnia and make it difficult to fall asleep. In essence, poor sleep causes inflammation, and inflammation makes it hard to sleep. So, even if sleep-related inflammation does not hurt your gains directly, it might do so indirectly since lack of sleep can lead to the hormonal issues mentioned earlier.

Performance

You need to perform your best in the weight room to build muscle. That means being well rested.

One single night without sleep might not hurt your muscle strength, so don’t worry if it’s a one-time thing.³

However, two or more nights without proper sleep quickly take their toll, with decreased performance and worsened mood state as a result.⁴ ⁵

Summary

While no long-term studies have examined the effects of poor sleep on muscle growth in strength-training people, we can be quite sure it’s something you want to avoid.

If you can.

Sometimes, life prevents you from getting the sleep you want or need. You’ll get some science-based tips on how to improve sleep quality at the end of this article.

However, the short-term effects are profound, and from everything we know about chronic insomnia, they don’t get better.

A single night without sleep lowers testosterone by ~24% and increases cortisol by ~21%. In addition, your muscle protein synthesis drops by close to 20%. In other words, you build one-fifth less muscle the day after a night without sleep.⁶

Now, even if you don’t get as much sleep as you’d like, it’s probably rare that you don’t get any at all. So don’t worry about one sleepless night. Poor sleep is not the same as no sleep. Still, it shows how important sleep is for your body’s anabolic (muscle-building) processes and that you don’t want to skimp on your Zs if you want to build lean muscle mass.

The Effects of Sleep on Body Fat

Obesity is a significant health issue worldwide. Most people associate gaining body fat with unhealthy eating habits and a lack of physical activity. And rightly so.

However, in recent decades, scientific research has identified poor and short sleep as potential contributing factors.¹

Multiple studies show a clear link between not getting enough sleep and increased body fat in all ages, from adolescents to seniors.

Interestingly, the relationship between sleep and body mass index (BMI) differs by gender. For men, less sleep correlates with higher BMI. In contrast, the relationship is U-shaped for women, meaning both too little and too much sleep can be associated with higher BMI.

The exact mechanisms connecting sleep to BMI are not fully understood yet, but some likely explanations exist. They include hormonal regulation of appetite and the body’s energy expenditure. Shorter sleep durations might also lead to poorer food choices (you’re more likely to eat junk if you’ve slept poorly) or simply more time awake to eat. Both things can contribute to an increased calorie intake.

Studies using different methods to assess body composition find connections between sleep problems and increased body fat, including longer time to fall asleep and frequent disturbances where you wake up during the night. Poor sleep can lead to hormonal changes that favor fat storage, like higher morning cortisol levels.

Chronic insomnia is a common sleep disorder, with ~10% of adults suffering from some form of it and another 20% experiencing occasional insomnia.⁷

Insomnia has been linked to weight gain and obesity. People with insomnia are also more likely to develop metabolic syndrome, a cluster of conditions—including high blood pressure, high blood sugar, body fat storage around the waist, and abnormal cholesterol or triglyceride levels—that together increase the risk of heart disease, stroke, and type 2 diabetes.

In short, poor sleep quality is consistently associated with increased body fat. However, the exact mechanisms remain unclear, although they likely involve appetite regulation, energy expenditure, and hormonal changes.

Lack of Sleep Makes You Eat More Junk

You eat more when you’re sleep-deprived. While it might not apply to hardcore bodybuilders and fitness enthusiasts who weigh everything on a food scale before they put it into their mouths, many people’s brains react to a lack of sleep by craving more food.

Lack of sleep messes with your leptin and ghrelin levels.

Leptin tells your brain that you’re full and works with your thyroid gland to control how your body stores and uses energy. When you sleep, your leptin levels increase. However, poor sleep means lower leptin levels than normal, fooling your brain into thinking you’ve not eaten enough.
Conversely, Ghrelin tells your brain when it’s time to eat. When you don’t sleep enough, ghrelin levels rise, telling your brain that you’re hungry and need more calories than you really do.

A strictly controlled study found that people ate 22% more calories the day after sleeping four hours than after a good night’s sleep.⁸ That’s ~500 calories more than they needed. And if that becomes a habit, it will result in rapid weight gain.

Sleep More, Eat Less

The opposite is also true.

When overweight men and women were instructed to sleep two more hours per night (and advised how to accomplish this feat), they automatically ate ~270 calories less per day.⁹ The control group, who slept their usual less than recommended 6.5 hours per night, increased their calorie intake slightly during the study period.

This study only lasted four weeks, but if the lower calorie intake continues, the participants who slept more would lose approximately 26 pounds in three years just by snoozing an hour or two more every day.

Too Little Sleep While Dieting Means More Muscle and Less Fat Lost

In one study, 36 overweight adults was instructed to continue with their daily routines, but reduce their caloric intake to 95% of their RMR, resting metabolic rate.¹⁰ That’s a weight-loss diet guaranteed to shed pounds.

Then, the participants were divided into two groups.

One group was told to continue with their usual sleeping habits.
The other group was instructed to sleep one hour less than usual, either by going to bed one hour later or getting up an hour earlier, five days per week. They could sleep in as much as they wanted the remaining two days.

After eight weeks, both groups had lost similar amounts of body weight, a bit over 6 pounds. So far, so good.

Those who slept their usual hours lost 83% body fat and only 17% lean mass. That’s a great result, considering strength training wasn’t part of the study. Had it been, their weight loss would have been all fat.
The sleep-deprived group, however, wasn’t so fortunate. While they lost the same amount of weight, 42% of that weight was lean mass, aka muscle mass.

Going solely by the scale, both results might look equally good, but sleeping too little could undermine your body composition goals (the proportion of fat, muscle, bone, and other tissues that make up your body weight).

Those results align with an earlier study, in which sleeping for 5.5 hours instead of 8.5 hours each night during two weeks of calorie restriction decreased fat loss by 55% and increased muscle loss by 60%.¹¹ In addition, the participants who only slept 5.5 hours experienced significantly more hunger during the day.

The Quality of Your Sleep, Not Just the Duration, Matters

While sleeping too little increases the risk of muscle loss and fat gain, how long you sleep is not the only factor. How well you sleep also affects lean muscle and body fat.

According to a recent study with close to 20,000 participants, muscle mass decreases even if you sleep enough hours, but your sleep quality is poor.¹²

Conversely, getting quality sleep time even if you can’t sleep enough hours prevents the fat gain sleep deprivation might lead to.

In other words, getting enough sleep plays a crucial role in maintaining muscle and preventing fat gain, but making those hours count is equally important.

Strength Training to the Rescue

If you think the above sounds like doom and gloom, it’s time for the good news.

High-intensity exercise can eliminate the risk of muscle loss during times when sleep is scarce.

In a recent 8-day study, 24 young men with regular sleeping habits were divided into three groups:¹³

Group 1 slept normally and didn’t exercise.
Group 2 slept four hours per night and didn’t exercise.
Group 3 slept four hours per night and performed high-intensity interval training on days 4, 5, and 6.

After five nights of only getting four hours of sleep, group two’s muscle protein synthesis (MPS) had dropped by a massive 19%. The MPS of group one remained the same, as expected.

Interestingly, group three’s MPS also remained high, even though these guys slept as little as group two.

In short, intense workouts maintains, and even boosts, muscle protein synthesis during sleep restriction.

Sleep and muscle: the effects of strength training

Now, this study only lasted eight days. If the experiment had gone on for weeks or months, exercise might not have completely prevented muscle loss. But the results are still striking.

Also, strength training is likely even more effective than bike intervals. Nothing prevents a catabolic environment and promotes muscle hypertrophy like lifting weights.

In other words, if you, for some reason, can’t sleep enough or well enough for some time, don’t stop training. Strength training protects your muscles by keeping your muscle protein synthesis rates, which would have otherwise declined significantly, up. Also, lifting improves the quality of the sleep you do get.¹⁴

That being said, you will likely perform and feel worse in the gym, and the risk of injury could be higher, so listen to your body and don’t push it if you’re sleep-deprived. Moderate exercise is good; going for personal bests might not be.

How Much Sleep Do You Need?

According to the Centers for Disease Control and Prevention, most people typically need 7–10 hours of sleep, depending on their age.

Teen 13–17 years: 8–10 hours
Adult 18–60 years: 7 or more hours
Adult 61–64 years: 7–9 hours
Adult 65 years and older: 7–8 hours

If you train hard, standard sleep recommendations might not be ideal.

Most athletes need at least 8 hours of sleep to feel rested, but almost none get as much as they feel they need.¹⁵

Instead of relying on a general number, get as much sleep as needed to feel good and rested and perform your best. Not only can insufficient sleep negatively affect your performance, muscles, and body fat, but it can also make you more susceptible to catching colds and other infections.

If you train in the afternoon or evening after a night of poor sleep, a nap during the day can restore cognitive function and boost performance. A long (35–90 minutes) nap is more effective than a short (20–30) nap.¹⁶ However, if you snooze too long, you might compromise the next night’s sleep, so try to strike a balance.

How to Sleep Better

It’s easy to say that you should sleep more or better. Counting sheep rarely helps, so how do you improve your sleep quality? Recent research has identified a number of things that could make an actual difference.

Regular Exercise

Aerobic exercise – walking, running, cycling, or swimming – is one of the top interventions for longer, deeper sleep. Aim for at least 30 minutes of moderate aerobic exercise most days of the week. Your health will thank you as well. Stay reasonably active during the day when you can, even if you have a desk job. Get up and move around regularly.
Lifting weights (or doing any other form of resistance training) is proven to promote better sleep. Notably, several studies have identified resistance training as perhaps the most effective exercise for promoting sleep duration and good sleep quality.

Nutrition

Avoid heavy meals close to bedtime. You want protein to keep your muscles happy during the night, but there are better choices than an all-you-can-eat buffet before bed. Casein protein is a popular choice to keep muscle protein synthesis elevated throughout the night. Simple carbs can help you fall asleep faster.
Caffeine is a stimulant and can disrupt sleep. It stays in your body for many hours and can disturb sleep for at least six hours after ingestion. Consider limiting your intake, especially in the late afternoon and evening.
Limit alcohol close to bedtime. While it may help you fall asleep, alcohol can disrupt your sleep cycle and reduce sleep quality.
Chamomile tea and valerian root can improve sleep quality without adverse effects. Melatonin is also effective.

Optimize Your Sleep Environment

Invest in a comfortable, high-quality mattress and pillows that support your sleeping posture.
Keep your bedroom dark (use blackout curtains if necessary), quiet (consider earplugs or white noise machines), and cool (around 60-67°F or 15-19°C). Light, noise, and heat are the enemies of a good night’s sleep.
Limit your screen time and reduce exposure to blue light from phones, tablets, computers, and TVs at least an hour before bedtime.

Healthy Sleep Hygiene Practices

Go to bed and wake up at the same time every day, even on weekends. According to several studies, doing so helps regulate your body’s internal clock and plays an important role in establishing a regular sleep schedule and achieving adequate sleep.
Mindfulness practices and meditation reduce stress and anxiety, which are common culprits of poor sleep. Try establishing a relaxing pre-sleep routine to help calm both body and mind and prepare you for sleep.
Naps can be great as a pick-me-upper. If you need to nap, keep it short (20–30 minutes) and early in the afternoon unless you need a longer snooze to maximize performance for a 1RM attempt or something like that.
Get plenty of natural light during the day, especially in the morning, to help regulate your sleep-wake cycle.

The more of these practices you integrate into your daily routine, the greater the chances that you significantly improve the quality of your sleep.

Sources: ¹⁷ ¹⁸ ¹⁹ ²⁰ ²¹ ²² ²³ ²⁴ ²⁵ ²⁶ ²⁷ ²⁸

Final Words

Any fitness enthusiast worth their salt knows how important consistent training and a healthy diet are to get the results you want. However, not everyone is aware of the impact sleep can have. Both the amount of sleep you get and the quality of it hugely impact almost everything in your life and the balance between muscle mass and body fat.

Quality sleep improves muscle recovery, makes it easier to gain muscle, and boosts performance. In contrast, inadequate sleep can lead to muscle loss and increased body fat. Getting sufficient rest optimizes your workouts and regulates hormones that control hunger, muscle growth, and fat storage, helping you achieve a more muscular and lean physique.

Prioritizing sleep is as crucial as your workout and nutrition plan. It ensures your hard work in the gym doesn’t go to waste, and a well-rested body not only performs better but also looks better.