How Your Body Maintains Muscle Mass When You Fast [overview + link to page w/ sources]

One of the big myths out there is that fasting will “burn” up your muscles, and you’ll waste away.

Sure, you can lose some muscle mass while fasting. But that’s mainly if you don’t have body fat to lose and you and/or you don’t take a smart approach.

I did some research for a recent blog post, so I thought I’d share a few of the physiologic principles here, along with a few related tips for success, as well as a link to the original post where you can find specific sources.

First, here are a few different things your body does to help maintain muscle mass while fasting:

1. During the first 12-24 hours, glycogen stored in your liver maintains your blood sugar. No problem (and no need to tap into muscle protein for energy). So for short fasts, there’s not really anything to worry about.

2. Once your ketones become elevated, they directly inhibit muscle breakdown. That means your body will selectively try to use other proteins instead (like protein from connective tissue, scavenged via autophagy, etc)

3. Ketones also make it so you don’t need as much blood sugar, because they’re an alternative energy source for your brain. That’s another way they preserve protein (which could otherwise be needed as a source of blood sugar, through gluconeogenesis).

4. After a while, growth hormone becomes elevated, which can help maintain muscles, and potentially help rebuild any that was lost after you finish fasting

Related to the above, here are a few things you can do to help maintain muscle mass when you fast:

1. For longer fasts (>24hrs), try to get your ketones up in advance. Ketones help preserve your muscles directly and indirectly (as described above), so the sooner you have them on board the better.

2. Continue exercising during and after your fast. Exercise stimulates muscle growth, even if you’re not eating anything. So physical movement may be the best tool you have to maintain your muscles–even when fasting.

3. Eat plenty of food (especially protein), before and after your fast. In other words, FEAST when you’re not fasting, and don’t try to restrict calories. Let your body know that food is available!

Overall, as long as you have some body fat to spare, you keep moving your body, and you eat enough food before and after your fast, muscle loss shouldn’t be a significant issue.

Here’s the link as well in case you’d like to take a look. :) That post also includes links to various scientific studies, and other sources.

https://fastingwell.com/fasting-muscle-loss/

Hope it helps!

Ben

(Naturally, this isn’t individual medical advice)