How to Prevent Muscle Loss While Fasting (Muscle Loss and Intermittent Fasting)

Siim Land

Want to try intermittent fasting but afraid of losing muscle mass? Don’t worry, read this article to know how to prevent muscle loss while fasting.

Losing Muscle While Fasting

Fasting and muscle loss – myth or truth?

You might have heard from bodybuilding experts and fitness gurus that you need to eat every few hour or else… or else you’re going to lose all your muscle mass.

I’m going to tell you right away that this is complete bullsh#t.

Fasting doesn’t make you lose muscle because think about it… Hunter-gatherers would occasionally go through long periods where they wouldn’t eat anything for a week. Did they die? Did they catabolize their muscle and lean tissue? No…

In fact, they became even more resourceful, sharper, more alert and focused so that they could catch some prey animals.

Losing their muscle mass would’ve been an evolutionarily unviable strategy.

Now hold on a minute…

We shouldn’t make false presumptions around romanticising some ideas. And it’s important to look at some research.

Let’s look at what science has to say about this?

Science of Fasting and Muscle Loss

One of the biggest reasons why fasting doesn’t equal muscle loss is because of growth hormone.

Under normal conditions, your body has only one spike of growth hormone in the morning and another one at night.

Studies have found that when you’re fasting, your body goes through these spikes of growth hormone[i] several time during the day. So, you experience surges of growth hormone more frequently when in a fasted state.

In fact, growth hormone increases exponentially by up to 2000-3000% at the 24-hour mark. #ARMEXPLOSION

When you look at the amount of GH increase then the micrograms aren’t that large, but you wouldn’t experience anything like that in a regular metabolic state. This boost is actually going to last for the upcoming several hours.

Another hormone that’s going to help you build muscle is testosterone.

  • Short-term fasting has been shown to increase Leutenizing Hormone (LH), which is a precursor to testosterone. In a study done on obese men, LH increased by 67% after 56 hours[ii]
  • Another study found that obese men saw a 26% increase in GNHR (Gonadotropin-releasing hormone), which is another testosterone stimulant[iii]. The same study found that men who were working out saw a 67% increase in GNHR, which led to a 180% boost in testosterone.

So, there’s plenty of hormonal benefits to fasting and I’d suggest that if you’re suffering from low testosterone or you can’t seem to build fat, then it’s just because your endocrine system is unable to produce its own testosterone. Some careful and strategic intermittent fasting can help your body to not be so lazy so to say and jack up your muscle building pathways.

Why Am I Losing Muscle While Fasting?

Nevertheless, there are many people saying that they’re losing muscle while fasting. Why is that?

First of all, it’s important to realize that not all weight loss or decrease in the equals muscle loss. Losing weight doesn’t mean you’re burning fat either.

If you’re eating a regular diet that doesn’t incorporate IF or is adequate in carbohydrates, then your body will hold onto more glucose as glycogen. It’s going to give you a much more fuller look like this puffiness and vascularity.

Once you start to fast or when you eat a low carbohydrate diet, then you’ll flush out some of that glycogen and water. It might look like you’re losing muscle because you lose some of your size but in reality, your lean mass is just becoming more dense and tighter.

With that being said, it doesn’t mean you can’t lose muscle while doing intermittent fasting. Of course, you can and you will if your body feels the need to do so.

There are 2 reasons why you may begin to break down your lean tissue.

(1) Gluconeogenesis While Fasting

First is gluconeogenesis – the conversion of protein into glucose.

Gluconeogenesis is driven by demand not by supply, which means that it happens when your body needs glucose for survival and the only source of glucose it can find is its own organs and muscles.

The reason you may trigger gluconeogenesis is that you don’t have access to other fuel sources, like fat. Your body isn’t keto-adapted to burning ketones yet and the next best thing it can think of is protein.

That’s why you’d want to get into ketosis as soon as possible when you’re doing fasting or even when maintaining a caloric deficit. The ketogenic diet will make you burn exclusively your own body fat while preserving muscle because ketones give more energy to the brain, which spares protein.

To prevent excessive catabolism, you’d want to deplete your liver glycogen first before starting to fast.

  • Make your last meal low carbohydrate so your liver could start producing ketones more rapidly.
  • Exercising on an empty stomach like walking or steady state cardio can also help you to get into ketosis faster.

After you flip the metabolic switch of starting to use more ketones for fuel, you’ll increase fat burning and protect your muscles because the body has access to an abundant fuel source which is your own body fat.

(2) Autophagy and Muscle Loss

The second reason why you may lose muscle while fasting is the inhibition of autophagy.

Autophagy is the cellular cleansing mechanism that recycles old and damaged cells into energy.

Studies have found that autophagy is needed for maintaining muscle mass[iv].

  • If you’re doing a caloric restriction diet but blocking the effects of autophagy, then you’re going to keep yourself in a semi-starvation state because your body will never switch into ketosis. This leads to gluconeogenesis and so on – the bad stuff.
  • If, however, you allow autophagy to kick in, whether that be through strict water fasting or a fasting mimicking ketogenic diet, then your also stimulating the other growth hormones we’ve been talking about so far and it’s going to preserve your muscle.

What it means is that if you want to burn fat, or if you want to prolong your lifespan, then you’re actually better off by avoiding all calories whatsoever.

Even as little as 50 calories of 2-3 grams of leucine will stop autophagy and shift you into a fed state. It’s going to be better for fat loss, for muscle sparing and for longevity, to avoid all calories during your fasting window.

Can Fasting Make You Build Muscle

But what about the opposite? Can fasting actually make you build muscle?

It depends on how hard you train and how many calories you eat during your feeding window when your not fasting. I’ll leave the nutrition aspect of it for a future video because I want to look at the hormonal side at the moment.

The body’s main anabolic pathway is mTOR (mammalian target of rapamycin). It’s going to trigger all cells in the body to grow – muscle, fat tissue and even some tumor cells. You want to maintain a healthy balance between too much and too little mTOR if you want to build muscle and live longer at the same time.

Studies have found that fasting lowers the expression of mTOR and IGF-1, which are both needed for cellular growth[v] by increasing one of their inhibiting proteins called IGFBP1.

A Hypothesis

Now, wait a moment…How can fasting help you to build muscle if you’re suppressing these hormones? I might be completely wrong here but here’s my hypothesis or bro-pothesis.

  • Fasting also improves your insulin sensitivity, which makes you better at utilizing glucose as energy and triggering protein synthesis.
  • mTOR and IGF-1 are both insulin dependent pathways, which means that you’ll become more cost-effective at their expression – you begin to need less mTOR to have a greater effect on building muscle. And I would suggest that combining it with autophagy allows you to gain the life-span prolonging benefits while alleviating the side-effects of aging.

So, you want to constantly maintain this balance and awareness about your body’s sensitivity to these pathways.

Intermittent Fasting and Muscle Loss

Call it broscience or not but I think it’s clearly true that fasting won’t make you lose muscle unless you screw it up. Unless you just randomly wing it and break the rules of your physiology.

Here’s how to prevent muscle loss while fasting

  • You want to get into ketosis ASAP when doing intermittent fasting.
  • You have to keep autophagy elevated and active
  • You don’t want to be releasing too much cortisol which will counteract testosterone
  • You should be eating a diet that teaches your body to burn fat and ketones for fuel for at least the majority of time so that when you do have to skip a meal or not eat for 3 days then you’re not going to cannibalize all your gains

If you want to learn more about how to build muscle with intermittent fasting and the ketogenic diet, then my book KETO BODYBUILDING is a must-read.

keto bodybuilding
keto bodybuilding

P.S. Check out my Keto // IF Program to learn how to do intermittent fasting properly

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