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Avid | 6 months ago (raw) | root | parent | reply | flag 
 This is false, the body needs amino acids for brain and organ function, the muscles are the body’s amino acid reserves. I’ve done OMAD, 16/8 20/4 and 72 hour fasts, I’m not saying they are bad for you, ketones are good fuel, but ketones aren’t a replacement for amino acids.
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Avid | 6 months ago (raw) | root | parent | reply | flag +1 
 The amount of muscle loss may be imperceptible if you re-feed and resistance train, but it’s happening at a low level when you haven’t eaten in the last 8-12 hours.
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freddms | 6 months ago (raw) | root | parent | reply | flag +1 
 Exactly. I think we are agreeing on more than we disagree!
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freddms | 6 months ago (raw) | root | parent | reply | flag +1 
 I have been fasting for 36-45 hours every week for over 3 years. I get into Autophagy in about 20 hours (I have learned to know when I'm in ketosis and then into Autophagy - after checking bloodwork many times). I'm 62 this year. Wife same age, fasting 3 years too. No problem. Muscle is fine but I'm also in good shape and work out nearly daily (but often not after my second day fasting). I would not go over 48 hours fasting based on the books I have read.

I'm not saying your body 'never' uses muscle to create amino acids during a fast. Your muscles are ALWAYS regenerating themselves so there is a constant replenishment of muscle. What I'm saying is you will not lose your muscles mass intermittent fasting or fasting for a day or two - largely due to the anti-catabolic effect of fasting (see below).

I also believe most of the data out there on amino acids are from companies selling amino acid compounds. Which is fine - I guess if you are a power lifter or your fat body mass is very low, you may need them? They are not going to hurt if you keep calories very low to get the benefits of fasting!

I think this is complicated and we are talking over each other and as the clip below shows, "It depends." Depends on your health, if you exercise, and getting to know your body.

And yes ketones are not a replacement for amino acids.

From ChatGPT.

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The question was, "Does proteolysis happen during extended fast?"

Proteolysis, the process of breaking down proteins into smaller peptides and amino acids, does occur during fasting.

In fact, studies suggest that proteolytic pathways are stimulated in most tissues during fasting, except for muscle tissue. In muscle tissue, the breakdown of proteins is inhibited during fasting, which is known as the “anti-catabolic effect” of fasting. This is because muscle protein breakdown is suppressed by the hormone insulin, which is decreased during fasting.

During fasting, the body breaks down proteins in other tissues, such as the liver, kidneys, and adipose tissue, to release amino acids that can be used as an energy source. This process is mediated by lysosomal pathways of proteolysis, which are activated during short-term starvation, and chaperone-mediated autophagy, which is activated during long-term starvation.

In summary, proteolysis does occur during fasting, but the specific pathways and tissues involved vary depending on the duration and type of fasting.