Question about fasting protocols

Does anyone know or have an educated guess on if doing a 48-hour fast once weekly would produce better benefits compared to fasting on 2 separate days per week? I was just wondering if the 48-hour fast would do better than two 24-hours fasts (Monday & Thursday).


Autophagy and ketosis would be greater after the 48 hour fast since it takes time to enter both. There is some of both after 24 hours, but I don’t believe nearly as much. My guess: 48 hours.


The 48-hour fast also lowers insulin and glucose levels much more than the two 24-hour fasts. The problem is getting people to adhere to that. Which is why the so-called 5-2 diet came into being: it wasn’t better results, it was better adherence.

Define “better”?

Like EnrQay said, a bit more autophagy (my guess is not much autophagy in humans at only 24/48 hrs), definitely more ketosis, which drives many improvements in metabolic health/signalling. Your glucose and insulin sensitivity will improve (and weight loss), assuming you don’t overshoot over-nutrition on refeed. If you can manage to do 48 hrs, and if weight maintenance or some weight (fat mass) loss is the goal, I would do 48 hrs. Not sure your age and if you do any exercise (especially resistance), but just keep an eye on your skeletal muscle, you don’t want to be eating into any of it during this fasting intervention.

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I think a loss of muscle mass is unavoidable and that will negate any possible benefits from the fast imo.

There are many advocates of intermittent fasting that believe you can fast without losing muscle mass. Peter Attia believes you can do up to one week.
“Can you maintain muscle during fasting?”


I adhere to the 16:8 protocol most days. This past week my wife was away…so I decided to try a 2-day fast. Going into it, I thought it would be a difficult struggle and that I"d feel hungry and miserable. I was quite surprised by how easy it was. I generally only eat one meal a day (evening)…but I tend to much a bit throughout the day (some fruit, handful of mixed nuts, etc). But during my 48-hour fast, I realized that my munching is a habit…a want, not a need. When I set my mind to not munch, it was easy. I plan to do a 48-hour fast at least a couple times a month…maybe once weekly. I’d be interested to hear of other people’s experiences. Anyone done a 7-day fast? Was it difficult…?


Good question…to me, better is simply more time in autophagy…and the supposed health benefits that result from autophagy. I know there aren’t many quantifiable results in the short-term…at least not ones that I’m willing to spend $$$ on. For me, the process of writing my book Rapamycin, mTOR, Autophagy & Treating mTOR Syndrome gave me a much better understanding of the importance of time-in-autophagy…so I decided to experiment with a longer fast.

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Yes, but the tiny very important detail per Attia:

“particularly if you’re resistance training”

I think that the fast-mimicking diet (FMD) overcomes this problem. Today I’m on the fifth day of my monthly FMD, which I’ve done more or less continually for the last six years. I never exercise intensely during the FMD (in order to keep IGF-1 low), and I’ve noticed no muscle loss at age 58, with weight-lifting ability constant.

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I haven’t tried ProLon…but I am well aware of Valter Longo reputation and work. Thanks for your suggestion.

Just do the FMD for 72 hours. Its easy. Eat 2 times (max 3 times) a day just fats and fiber and do not exceed 600 kcal per day. Do not exceed 600 kcal!!!

What to eat:

  • Avocado have between 300 and 400 kcal
  • Olive oil and omega 3
  • green salad.

Make a salad with avocado, olive oil and green salad.

Do not eat:
cabs, proteins, …

This is the best fasting hack ever.


You’ll still lose muscle mass.

Peter Attia discuses here (45 mins) how TRF leads to a negative shift in body composition. Reduced muscle mass negatively impacts glucose sensitivity and increases frailty so you’re really robbing Peter to pay Paul.

For longer fasts (ie longer than 40 hours), I monitor a few things that are more important to me than potentiel benefits of fasting: work capacity, workout capacity and sleep quality. As long as I can work, work out and have good restoring sleep (according to Whoop), I keep fasting, and I start to eat (first meal: sauerkraut) as soon as one of those things seems to be compromised. I usually reach 80-90 hours.


Thanks for sharing your personal experience and insights. At the end of my recent 48-hour fast (my first), I realized that I could have gone on longer…I was not ravenously hungry. I will keep your metrics of work capacity and workout capacity in mind when I attempt a longer fast.


you’re on a site called rapamycin news… if you’ve taken rapamycin, every cell it reaches thinks you’re completely out of fuel. i’m no expert. but seems to me the SWITCH that says you’re out of fuel is much more powerful than things that lead to that switch. like fasting. that’s point #1. point #2 is we have no idea how much fasting does what. people say “generally this” and “generally” that. from what I’ve read, 3 days of fasting is a snap for your body. i’ve gone a day without eating no prob. i’ve only done 3.5 days max tho. seems to me rapamycin should beat a fast for less than 5 day hands down. What I try to do is never have more than 2 meals a day. and no snacks (almost ever. i’m human. but snacks are dumb is my motto) You just don’t need food too bad unless you wanna baby your mood. and less food = longer life. that is about the only thing known about longevity. everything else is just educated guesses and heresay it seems to me. but again, NOT and expert. Just a computer programmer interested in nutrition.

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I highly recommend this book:
The Intermittent Fasting Revolution: The Science of Optimizing Health and Enhancing Performance

and video:

Mark Mattson is the top expert in the field of fasting.


I am thoroughly unconvinced by the benefits of fasting for longevity. In the ITP, calorie restriction must be initiated early in life to positively impact life span. Additionally it creates small and frail mice that are likely less resilient outside the artificial environment of the laboratory.

There is now ample evidence that shows that TRF is no better than traditional dieting for weight loss when calories are matched. Further most people who follow TRF tend to consume the majority of their calories at dinner. This goes against the body’s circadian rhythm so negatively affects sleep and leads to sub optimal energy partitioning. Finally, anecdotal evidence from many respected practitioners (e.g. Peter Attia), plus some recent preliminary research, suggest that fasting and TRF both lead to a loss of lean body mass.

As MK says, why use a ‘dirty’ drug like fasting for autophagy when a specific drug like rapamycin is available and effective? I certainly do not believe that the benefits are additive.

MK was talking about metformin (being a dirty drug). And by saying that rapamycin is a clean drug, you have to forget that we don’t have any biomarkers (yet) and that while it does have a clearly defined mechanism of action (TOR, complexes 1 and 2), we actually still don’t know how that really works and this reasoning for rapamycin is a bit circular, as TOR is defined by rapamycin (Target of Rapamycin)…

In contrast, fasting is something our metabolism has had millenias to adapt to, to make the best of it. That makes it quite “clean” in my view. And I kind of like the research in this domain.

I too want to keep muscle mass, but I’m not obsessive about it, that is, I don’t want to maximize muscle mass either, just avoid a loss. Thus I tend to favor alternating fasting (with rather aerobic exercise) and protein loading (with resistance training). And from where I stand, I don’t see research confirming or infirming this stance. For now.

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True, on longevity, I’m also not convinced. After all, if CR (caloric restriction) doesn’t improve lifespan starting at middle age (in clinical studies) why would fasting?

But for healthspan it (fasting) seems a reasonable bet. One more piece of data here this week:

The new research is published in Natureand was conducted by Imperial College London researchers. They observed how fasting led to the gut bacteria increasing production of a metabolite known as 3-Indolepropionic acid (IPA), which is required for regenerating nerve fibers called axons—thread-like structures at the ends of nerve cells that send out electro-chemical signals to other cells in the body.

This novel mechanism was discovered in mice and is hoped to also hold true for any future human trials. The team state that the bacteria that produces IPA, Clostridium sporogenesis, is found naturally in the guts of humans as well as mice and IPA is present in human’s bloodstreams too.

The length of the regrown axons was measured and was about 50% greater in mice that had been fasting.

Professor Di Giovanni said, “I think the power of this is that opens up a whole new field where we have to wonder: is this the tip of an iceberg? Are there going to be other bacteria or bacteria metabolites that can promote repair?”

Research Paper:

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