The Effects of Sleep on Muscle Growth and Fat Loss

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What if I told you that there is one supplement out there that can effectively:

  • Provide you with much more energy.
  • Improve your fat loss efforts.
  • Help you build more muscle mass.
  • Improve your hormonal profile.
  • Regulate your appetite.

And what if I told you that this supplement is completely free?

What’s that?

No, it’s not the latest “Fat-burning furnace 3000” or “Boost your testosterone through the roof” product.

It’s sleep.

And today, we’ll take a look at this often ignored ‘supplement’ and how it affects muscle growth and fat loss.

Sleep and Muscle Growth

Sleep and muscle growth are harmonious.  Not getting enough sleep will directly impact your muscle growth on two main fronts:

  1. It will reduce circulating levels of two very important hormones – IGF-1 and testosterone (1, 2, 3).
  2. It will impact your performance in the gym leading to sub-optimal training.

As you probably know, testosterone directly influences muscle hypertrophy. It does so by binding to androgen receptors, going to the cell’s nucleus, and increasing protein synthesis. It also plays an important role with mTOR pathway (the primary cellular pathway responsible for muscle growth). It directly inhibits the activity of other proteins that block this pathway.

IGF-1 also works through the mTOR pathway to increase protein synthesis. It also plays an important role in satellite cell recruitment and proliferation.

This is an important process of recruiting more myonuclei for each muscle fiber, thereby improving the muscle’s potential to grow.

And if you’re not getting sufficient sleep, you are inhibiting muscle growth on multiple fronts. And it doesn’t stop there:

Are you familiar with catabolism? That dirty process that breaks down tissue, including muscle.

We established that sleep deprivation decreases levels of testosterone. And this is bad because testosterone is an inhibitor of myostatin.

Myostatin is the jerk that directly undermines IGF-1’s efforts by blocking satellite cell recruitment and proliferation. It does the opposite of IGF-1, which is bad.

And if things weren’t bad enough as is, sleep deprivation also increases your levels of cortisol. Now, acute raises of this hormone are to be expected and are beneficial. It normally peaks in the morning as you wake up and during your workouts.

However, when you have chronically elevated cortisol all sorts of nasty stuff happens: protein synthesis is inhibited, protein breakdown is accelerated, you retain more water, and it directly impacts your cardiovascular health.

Sleep and Fat Loss

We already established that insufficient sleep directly impacts your testosterone levels. And aside from big T’s positive effects on muscle growth, libido, and energy, it also impacts fat loss in big ways.

One study suggests that higher testosterone levels increase BMR by 7 to 13% and lean body mass by 10% in both normal men and those with muscular dystrophy.

This study suggests that having higher levels of circulating testosterone directly inhibited fat cell formation.

And in this study, the researchers concluded that higher levels of testosterone make it easier for the body to metabolize fat tissue.

But enough about testosterone.

This study set out to determine whether sleep had an impact on dieting efforts. The participants were ten overweight and healthy people between the ages of 35 and 49.

Potential participants who had self-reported sleep problems, had an excessive intake of alcohol or caffeine, were smokers, or had abnormal findings on medical history were excluded from the study.

The ten people who completed this were pretty much healthy, average Joes.

They had to stay in bed for either 8.5 or 5.5 hours each night for two weeks. After at least three months, their conditions were swapped. They were put on a calorie-restricted diet at 90% of their resting metabolic rate, with their meals weighed to ensure that the caloric intake was controlled.

Now, the results were interesting:

Those in bed for 8.5 hours slept, on average, for 7 hours and 25 minutes. Those in bed for 5.5 hours, on average, clocked in 5 hours and 14 minutes of sleep.

Food intakes were identical ~1450 calories with an estimated energy expenditure of 2150 calories for a reasonably-aggressive 700 calorie deficit per day.

A total of 48% of their calories came from carbs, 34% fats, and 18% protein (which is a bit low, ~65 grams a day, but then again, they didn’t have that much muscle mass to protect in the first place).

Now, the interesting part is this:

Both groups lost roughly 6.6lbs of bodyweight.

The 8.5 hours in bed group lost a reasonable 50/50 fat and lean mass.

The 5.5-hour group?

They lost 20/80 fat and lean mass. Damn, only a fifth was actual fat mass.

And do keep in mind that their circumstances were damn near the same, except for the sleep. As it turns out, sleep and fat loss go hand in hand.

But it doesn’t stop there: the group deprived of sleep reported higher levels of hunger, which was accompanied by higher levels of ghrelin – a hormone that promotes hunger.

Some clarifications about this study:

  1. The subjects were sedentary. And we know that lifting weights while dieting is a crucial factor for muscle maintenance.
  2. As I pointed out, protein intake was quite low, just 65 grams per day. A good rule of thumb is to keep it at 1 gram per pound of body weight.
  3. Lean mass losses in both groups include water, not 100% is pure muscle mass.

But seeing as their conditions were the same, such big differences in actual fat loss is telling us something:

If you’re looking to lose fat and keep your precious muscle, you need adequate sleep, a caloric deficit, regular strength training, and, for the love of God, more than 65 grams of protein per day.

The Bottom Line on Sleep and Muscle Growth and Sleep and Fat Loss

We often sacrifice our sleep to get more work done or to have some fun. And don’t get me wrong, not getting enough sleep occasionally won’t wreck you. But if you repeat that over and over again, you’ll accumulate what scientists refer to as sleep debt.

The extra time you spend awake will be less productive, your health will take a hit, and your efforts in the gym will be in vain.

But do you know what helps with that?


Every night.

For 7 to 9 hours.

Follow me / Pump Some Iron on Instagram for updates @pump.some.iron

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Hey, I'm Brian, the creator of I've been weightlifting / bodybuilding for 20 years and now I'm ready to share some knowledge. Check out my About Me page to hear my story.

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