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Extended Fasting Causes Muscle Loss

Extended Fasting Causes Muscle Loss

Extended fasting has gotten a lot of attention lately. Extended fasts are fasts with little to no calories for longer than 24 hours. NOTE: This is referring to extended fasting of longer than 24 hours, not intermittent fasting which is totally fine as long as you hit your protein goal for the day.

Some extended fasting practices recommend only eating every other day. This may cause a drop in weight; however, some of that loss will be muscle loss, not what you want.

I am not sure if it is because it feels like a simple way to lose weight or why it is so popular in the keto community. I personally have never done extended fasting. I like to eat food and I do not want to lose muscle.

There was the most interesting study comparing alternate day fasting, where participants ate zero calories on alternate days, versus lowering calories every day and not doing any fasting. (CLICK HERE for the study)

The reason many people do extended fasting is to enter a stage of autophagy. Autophagy is when you turn over bad or damaged cells. The body takes the cells apart, removing any damage and rebuilding new cells from what is left. This can be an effective tool for people who are very sick with illnesses such as cancer, organ damage, etc. The body can in some cases turn over these bad cells and make new healthier ones. Fasting also induces more apoptosis which can be even more helpful in these cases. Apoptosis is where the body kills and removes damaged or bad cells that cannot be recycled.

But there is way too much put into autophagy from fasting gurus. It is put out there as “the fountain of youth” and you only get the benefits of it when eating nothing for long periods. This just isn’t true. First, autophagy is happening all the time at varying levels. Yoshinori Ohsumi, the Nobel prize winner for his research on autophagy, estimates that we turn over all our protein cells in our body in about 3 months. And that is for an average person doing NO fasting! Another study estimated that up to 20% of our daily basal metabolic rate (BMR) is from autophagy. And as you can see in this study, the alternate day fasting group experienced no favorable changes in autophagy gene expression!

Guess what stimulates autophagy as much if not more than fasting? Exercise and strength training! And you build muscle instead of losing it! THIS study showed that exercise increased autophagy in the brain and peripheral tissues. THIS study (and THIS one, and THIS one and many others) show the increase in autophagy from exercise. In THIS study subjects got continuous glucose infusions while doing exercise and had greater autophagy signaling that those doing a 36 hour fast. Exercise intensity more important than diet (fasting) for activating autophagy as THIS study shows.  It states, “the most effective strategy to activate autophagy in human skeletal muscle seems to rely on exercise intensity more than diet”.  I personally would rather eat a filet mignon for a lean protein boost and lift weights to enhance my cellular health.

And we have seen this time and time again with clients. Mike sent us his results after one week where he did a 3 day fast. He lost only 1 pounds of fat, but lost over 3 pounds lean mass. We see this ALL the time with clients that have to rebuild muscle they lost with extended fasting.


More studies like THIS one have shown this including this study that showed people lose over a pound of lean mass in the first day or two of fasting, then about 1/4 pound per day after that. So if starting the fast keto, you might be able to assume you will lose 1/4 pound lean mass per day from the start (instead of over a pound at first). But even if this is true, 1/4 pound of muscle is significant.

Extended fasting may be a helpful tool for someone with cancer or a serious illness that wants to purge unhealthy cells; however, if weight loss is your goal, extended fasting will just result in making you weaker with less muscle mass. Less muscle mass means a lower BMR so you will need less calories just to maintain your weight. So as with anything, your goals are important. For fat loss, general health, or keeping disease away, eating a well formulated ketogenic diet is what you want. Long Term Fasting isn’t needed.

We don’t recommend extended fasting for weight loss or general health. The negatives out weigh any small benefits from autophagy. If autophagy is your goal, do some strength training and exercise instead. 

A better way to lose fat would be a protein sparing modified fasting approach.

Click HERE to learn more about Protein Sparing Modified Fasting.


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Maria Emmerich

Maria is a wellness expert who has helped clients follow a Ketogenic lifestyle to heal and lose weight for over 20 years. She has helped thousands of clients get healthy, get off medications and heal their bodies; losing weight is just a bonus. She is the international best selling author of several books including "Keto: The Complete Guide to Success on the Ketogenic Diet.".


  • Julie Harris says:

    It makes sense that people would lose muscle mass because the study says it was conducted on lean people. I would guess that they didn’t have much fat to burn. I would like to see the same study on over-weight or obese people who have fat stores. It is stored energy and it is there to be burned. There are some many differing opinions and each camp says they have the science to back it up. Oi vey!!

    Thanks so much to you and your family for all that you do to help educate and encourage those of us who struggle with our health!!

  • Michael Fitzgerald says:

    Sooooo interesting!

    Glad to see that the studies support what I have personally experienced and seen anectdotally with over 40 years of weight training and being around people who do resistance training.

    From what I’ve seen, people who do resistance training AND eat lots of protein have better physiques, more lean muscle mass, and more energy than people who fast.

    • Maria Emmerich says:

      100% And we have had tons of clients who followed that advice and lost a lot of muscle and are now following us to regain that lost muscle.

  • Cathy P in AZ says:

    Maria and Craig – you have changed my world with PSMF and helped me break a very long weight loss plateau! I feel so much better than I did before doing longer fasts. I am seeing such a big difference with higher protein, weight training and short HIIT workouts. Thank you for always giving us such valuable information. ❤️👏🏼

  • Brian says:

    I see several links to different studies but I am not seeing the link to the specific study this article is based on. Can you provide that link?

  • Sarah Hardy says:

    I’d like to see what the results would be on overweight or obese people.
    Another thought I have is, that I think people forget is that our skin and blood vessels are in part made of proteins. So it stands to reason that we would lose some “muscle mass”. As we shrink our skin shrinks and so do all those blood vessels and capillaries that were supplying blood to those ever expanding fat cells. I’m still skeptical of this study, as it seems that there might be an agenda here. 🤷🏼‍♀️
    Thank you for all you both do and thank you for sharing with us.💞

  • Wenchypoo says:

    ….and one more shout-out for P:E–my husband has only been doing it casually for about a month, and his doctor said yesterday (at his appointment) that he lost 8 lbs.–this without him even really putting his nose to the P:E grindstone. I know this doesn’t sound like much, but he lost 40 lbs. on keto, regained half of it back, and has been stagnant throughout the pandemic. I guess his body has become resistant to weight loss. At least the scale is once again moving in the right direction! Let’s hope it KEEPS going that way.

    I’ve been making your PSMF recipes, but not really adhering to our macros (lazy P:E, I guess). I’m down 10 lbs., and he lost 8. I guess just by simply raising the protein, and cutting the fat, we’re still seeing some kind of benefit. Imagine if I were to really knuckle down and adhere to our macros…

  • Magdalena says:

    Thank you for this information. Makes sense! So, my question is do you think I can still making 16/8 fasting?

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