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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