KetoFasting: The Dark Side of Fasting & Ketosis (+How To Use Cyclic Ketosis To Fix The Issues)

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Dr. Joseph Mercola, my friend, multiple-time podcast guest, guy who thinks way outside-the-box and seems to always be discovering some new cutting-edge way to enhance human health and longevity, and one of the world's foremost authorities on alternative health, has just written a guide to using the principles of ketogenic eating, meal planning, and timing to treat disease, promote weight loss, and optimize health.

The new book is called “KetoFast: Rejuvenate Your Health with a Step-by-Step Guide to Timing Your Ketogenic Meals.

In the new book, he explores the profound health benefits that result when ketogenic living and well-planned fasting are combined. Topics include:

  • How our food is making us sick and what we can do about it…
  • The physiology and mechanisms of fasting, including stem cell activation…
  • How the cyclical ketogenic diet–with fasting included–differs from the conventional keto diet…
  • How fasting works and how safe it is for you…
  • How regular one-day fasts support fat burning and detoxification while minimizing hunger and side effects…
  • How to monitor your progress with lab tests…
  • And much more…

During our discussion, you'll discover:

-The fascinating history of fasting among different religions and cultures…8:25

  • Dr. Mercola's book was originally written to learn to optimize multiple day water fasting
  • Most religions integrate fasting into their practice (speaks to its efficacy throughout history)
  • It's one of the best ways to express care for your spirit, especially when combined with meditation, gratitude, solitude, etc.
  • Therapeutic fasting:
    • Calorie restriction to activate metabolic processes to catalyze the healing process
    • Fasting didn't become popular in the U.S. until the 1800s with the natural hygiene movement
    • Became more popular when Herbert Shelton popularized it in 1911
  • TrueNorth Health Center

-Autophagy, and why Dr. Mercola thinks of a fast as a “free stem cell transplant”…16:45

  • Different varieties of fasting:
    • Intermittent (the foundation)
    • You need more than intermittent to get the max effect of autophagy
    • Fasting mimicking diet, water diet
    • Hybrid of the two, minimize the harmful effects
  • Autophagy:
    • 3 types
      • Micro
      • Macro
      • Chaperone-mediated
    • You activate autophagy with the keto fast
    • Dr. Mercola does not recommend a long-term water fast
    • Free stem cell transplant is what happens during the regeneration phase, after the autophagy phase
    • The magic happens during the refeed and strength rebuilding; similar to a growth hormone injection
    • Do a 42 hour fast, in which you eat 300-500 calories 2x per week

-How fasting affects intestinal stem cell function…24:20

  • Extended fasting helps reduce gut permeability by stimulating brain/gut pathways
  • Consider fasting before other treatments or supplements for repairing the gut
    • Certain supplements will inhibit autophagy: colostrum, B12
  • AMP-k and mTOR
    • It's your friend; The higher the better
    • A nutrient sensor
    • Puts your body in “repair mode”
    • See Saw: AMP-k up, mTOR down, vice versa

-What nutrients you need to optimize autophagy…34:08

-How ketones protect the brain from excess hydrogen peroxide…46:00

  • Fats and carbs are fuel sources; broken down by enzymes
  • Oxygen receives electrons from the food you're digesting in the form of hydrogen (which is converted to water)
  • Most people are metabolically inflexible; can't burn much fat for fuel
  • Ketones increase Nicotinamide adenine dinucleotide phosphate (NADPH)

-Why Dr. Mercola changed his mind about the efficacy of water fasting as a metabolic intervention…50:55

  • We in the 21st century are exposed to chemical and industrial toxins not historically known to humans
  • Toxins are stored in our fat
  • When you fast, you release these toxins
  • Cause unpleasant side effects and symptoms
  • 2 phases:
    • Convert fat soluble to water soluble (not a problem)
    • Attach molecules to the toxin
  • You need frequent refeeds to fuel the process of eliminating the toxins and enhancing detox pathways
  • A keto fast (42 hours, 300-500 calories) 2x/week is far more powerful than an occasional multi-day water fast or even fast mimicking diet

-What Dr. Mercola views as the “dark side of fasting”…55:00

  • Detoxification impairment
  • Compliance: people just won't do it
  • How Dr. Mercola recommends Ben improve his own fasting strategy:
    • Ben takes essential amino acids for protein during extended fasts
    • Don't eat meat protein (branch chain amino acids)
    • Take collagen protein
  • Drawbacks to long-term ketosis
    • Requires significant calorie restriction
    • Women can develop thyroid impairment
    • You simply weren't designed to do it
    • Fasting primes your body for improvement; the real magic happens in the refeeds

-What is “keto fasting,” and how cyclical ketosis addresses the above issues…1:00:13

  • You must be metabolically flexible
    • Eat in a 4-6 hour window per day for 4 weeks
  • Branch chain aminos: leucine, isoleucine, valine
    • Eat these on the refeed, not during the keto fast
    • Don't activate mTor along with autophagy
  • Cyclical approach:
    • Keto fast 2x/week
    • Every day intermittent fast
  • Strategies to deal with hunger or appetite cravings:

-How sauna use supports a fasting protocol, an ideal sauna setup, and sauna dos and don'ts…1:07:45

-And much more!

Click here for the full written transcript of this podcast episode.

Resources from this episode: 

-My previous episodes with Dr. Mercola:

KetoFast: Rejuvenate Your Health with a Step-by-Step Guide to Timing Your Ketogenic Meals for research studies

Ben's Switzerland healing retreat at Paracelsus

The Complete Guide To Fasting by Jason Fung

TrueNorth Health Center

My interview with Dr. Satchin Panda

SEED Probiotic blend

ATP science

-Dr. Mercola’s “autophagy tea” before my nightly fast to also limit mTor activation and increase autophagy:

Pomegranate Pulled Apart podcast from ATPScience


HVMN Ketones

“The Longevity Diet” by Dr. Valter Longo

Kion Aminos

Kettle & Fire Bone Broth

Aloe Gel

Lucy Nicotine gum

Saunaspace sauna

Near-infrared bulbs

Dr. Lawrence Wilson's book “Sauna Therapy For Detoxification & Healing”

Episode Sponsors:

Kion: My personal playground for new supplement formulations. Ben Greenfield Fitness listeners receive a 10% discount off your entire order when you use discount: BGF10.

Clearlight Saunas: You can be sure that I researched all the saunas before I bought mine and Clearlight was the one that stood out from all the rest because of their EMF and ELF Shielding and their Lifetime Warranty. Use discount code: BENGREENFIELD to get $500 off your sauna and a free bonus gift!

FitVine WineDon’t let the word “less” fool you – FitVine wines offer rich flavor profiles and the alcohol content (13.4 – 13.9% alcohol) you’d expect from a fine wine. Use discount code: GREENFIELD10 for 10% off your order.

Do you have questions, thoughts or feedback for Dr. Mercola or me? Leave your comments below and one of us will reply!

Ask Ben a Podcast Question

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71 thoughts on “KetoFasting: The Dark Side of Fasting & Ketosis (+How To Use Cyclic Ketosis To Fix The Issues)

  1. Daniel Ackles says:

    Does supplementing with creatine monohydrate stimulate the mtor pathway during days you would be fasted on collagen/ bone broth? If so, could I just not take creatine on the “fasted” days?

  2. Ben says:

    The paudarco that’s linked is not powdered. Does that matter?

      1. BEN DIEUGENIO says:

        Great I’ll buy that one next time. Do you ever have issues with the rest of the ingredients not dissolving? I’ve been mixing with 12-24oz of water and still always clumps and strings. It pretty much seems like only the quercetin gets dissolved all the way. All in all it tastes great but I feel like I’m only getting 1/4 of the benefits because of how much is left. Are these brands tried and proven? I’ve only had bad luck with bulk supplements and I’m pretty sure it’s the glycine causing this. I hope that these are the brands you use and not just the ones that give good affiliate bonuses as I genuinely trust you and bought them purely because of you and mercola. Hopefully the clumping is normal

  3. Dustin says:

    Dr. Mercola mentioned very briefly that a person wouldn’t want to be on berberine long term. Why not? I got my dad using this to help manage his blood sugar which is working really well but now I’m concerned as to what the disadvantage might be. Thanks for all your work!

  4. Shawnda Kovacs says:

    This says that garcinia (one of the supplements in mercolas ‘tea’) inhibits ketogenesis. Thoughts on that?

  5. Rachael says:

    Hi Ben,
    I’m just listening to this podcast now and had to pause to write in to tell you how excited I am to hear you and Dr Mercola have both listened to the ATP science podcast. I’ve been a listener for a few years. Lots of insight to be had with these guys. Check out what their article (Matt) has to say about combining black pepper with turmeric…not good.
    Thanks again for all you are doing in this world of health, longevity and fitness!

  6. shawnda kovacs says:

    Sorry! One more question! I’m reading
    I’m 110 lbs and probably 16% body fat. I thought with keto, I should be eating 72 g of protein per day. But the above article almost seems like I should be even closer to 60? Is that right? And are you saying, I should be even lower on non strength training days or just on fasting days with cyclical protein?

  7. William says:

    Do you strain the autophagy tea or simply stir and drink?

    1. I usually don't strain and blend it together.

  8. sam y says:

    Hi Ben ,Dr Mercola, Dr Axe

    Any thoughts on this recent article that says cheat days on keto-diets may increase blood vessel injuries. Participants size is small though. If so, will regular dosing of vitamin c counter this risk.
    MNT : Keto diet: A ‘cheat day’ may undo benefits and damage blood vessels

  9. Greg P says:

    In this episode you say that Leucine is a BCAA and should be avoided during a fast but I use your Kion Essential Amino Acids and it says Leucine is one of the Essentials. So does that mean don’t take your Essentials during a fast?

    1. There are a couple very key differences… The BCAAs without the presence of the other EAAs does not get well absorbed/utilized by the muscle for protein synthesis, and is effectively burned as fuel in the form of carbs (and spiking blood glucose)… Kion Aminos do indeed contain Leucine (a very important amino acid for building muscle), but it is at an amount that won't cause spike blood glucose and is in presence of the other EAAs, meaning it is actually well-absorbed/utilized by the muscles.

  10. Mary E says:

    I ordered the items for the autophagy tea but in the recipe there was no mention of how much water to add and is the recipe for one serving? Thank you for all the health hacks….keep up the amazing goodness.

  11. KP says:

    Dr Mercola not concerned with apparent ketogenesis inhibition with Garcinia? See article below

    1. Per Dr Mercola: “You are citing a forty year old study… Time to update your sources:

      Hydroxycitric acid, extracted from the dried fruit rind of Garcinia cambogia, has been demonstrated to inhibit de novo fatty acid synthesis, promote fat oxidation and decrease appetite.
      Márquez, F, Babio, N, Bulló, M and Salassalvadó, J 2012. Evaluation of the safety and efficacy of hydroxycitric acid or Garcinia cambogia extracts in humans. Critical Reviews in Food Science and Nutrition 52, 585–594

      Hydroxycitrate, an inhibitor of ACLY that causes cytosolic AcCoA depletion, protein deacetylation, and massive autophagy in all studied organs in mice
      Onakpoya I, Hung SK, Perry R, Wider B, Ernst E. The use of garcinia extract (hydroxycitric acid) as a weight loss supplement: a systematic review and meta-analysis of randomised clinical trials. J Obes 2011;

      The depletion of nucleo-cytosolic acetyl-CoA activates AMPK and inhibits the mechanistic target of rapamycin (MTOR) complex I (MTORCI), hence arresting anabolic reactions and stimulating autophagy.
      Galluzzi L. Pietrocola F. Bravo-San Pedro J.M. Amaravadi R.K. Baehrecke E.H. Cecconi F. Codogno P.
      Debnath J. Gewirtz D.A. Karantza V. et al. Autophagy in malignant transformation and cancer progression. EMBO J. 2015; 34: 856-880”

      Hope this helps!

      1. Lorina says:

        I have a question about the linked HCA/Garcinia Cambogia: I bought the linked brand without looking at the ingredients. When I got i found it had maltodextrin. Is this the variety you would buy? Is maltodextrin safe?

  12. Vincent Robert says:

    Hi Ben,

    very good talk!!

    Do you have any discount for the SaunaSpace?? And which one is best… SaunaSpace or Clearlight Sauna??

    Thanks for your time!

    Keep the passion!

    1. I don't personally use SaunaSpace, but trust Dr Mercola's recommendation. I have a Clearlight Sanctuary and love it. It has EMF mitigation, gets nice and hot, has a cool sound system (if that's your thing) and the model I have is large enough to do yoga/stretching… which takes it next level.

      1. Vincent says:

        thanks for the info!!

    2. Read my article and watch my interview with Sauna Space owner

      He will be launching less expensive sauna soon and better bulbs on June 1

      1. Vincent Robert says:

        Thank you Dr Mercola!!
        I have ordered my near infrared SaunaSpace!!

  13. Will says:

    Would you ever consider doing a round table with different professionals. You produce alot of content and it seems like good content. Im a novice in this world at best and don’t have alot of time and money to invest in products or reading articles on pub med (teacher and father of 2 boys) But so much information is being thrown at me from these podcasts its hard for me to dig into one area. The guest you had at your house that discussed the carnivore diet had a really compelling argument from his point of view. I even heard him put down some of Mercola’s ideas especially regarding the Autopaghy tea. Dr. Merola comes on days later and presents his ideas which contradict the Dr. thats into the carnivore diet. It makes my head spin. Would love for them to sit down and go back and forth agree or disagree. I am also interested in buying a sauna or building one. I went to Dr. wilsons site based off of Dr. Mercola’s recommendation. Dr. Wilson to me recommends making your own sauna with materials to me sound awful-PVC pipes, polyester fleece, paint cloth from home depot, crappy lights, cutting cords and splicing. wouldn’t this just create awful off gassing chamber?

    Thank you for what you do Ben

    1. It's a cool idea… While it may seem overwhelming trying to figure out who's way is best, I think it's important to note that no diet is perfect for everyone. The very thing that works for one person could cause an autoimmune response in another. That's why I try to feature guests that offer unique perspective, even if some of it may seem contradictory to other guests ideas.

    2. You misunderstood Paul. I am actually interviewing him soon. He did not contradict what i said. I don’t recommend these polyphenols continuously, only when you are fasting. Paul is currently not fasting. I will discuss that with him on my interview

  14. Shawn says:

    Autophagy***** oops

  15. Shawn says:

    Great podcast!

    Does having MCT oil in your coffee or bulletproof coffee break apothogy fasting? Thanks Ben.

  16. Philippe says:

    Hi Ben and Dr. Mercola!

    Great podcast once again! Are you guys aware if there’s a way to test our NAD+ levels in the body to see which supplements and/or protocols really moves the needle and which doesn’t? I’ve been looking on google and it doesn’t seem to have much information on testing NAD+ levels… or I’m not looking at the right place. Can it be done via a simple blood test or it is more complex than that?

    Thanks for your input on that and looking forward for your next podcast together!

    1. Telomere length and inflammation would probably be the top two.

  17. SlyNate says:

    Can you comment on the potential liver toxicity of Pau d’ Arco? I seem to have read that when consumed over the long term you can run into liver issues.

    Is this a non issue and how frequently do you recommend drinking this tea? Take it every night or cycle of at times as well?

    1. I have not seen that, but feel free to fwd research and I will take a look. Often the dosage is important to pay attention to.

  18. Joe says:

    I had never heard the comment about butyrate blocking autophagy. I have been doing IF but with some butter during the fasting period (in my coffee). Would you advise against that in order to get the maximum autophagy benefits?

    1. Grass fed butter is not going to be especially insulinogenic and won't knock you out of Ketosis. But, yes, technically the butter will break your fast and may diminish some of the autophagy.

    2. That is because you, like most people that discuss this, are not scouring the literature

      When supplemented to starved cells, the short-chain fatty acid butyrate, which can be catabolized to AcCoA, maintained high cytosolic AcCoA, increased protein acetylation, and inhibited autophagy.

      Mariño G, et al. Regulation of Autophagy by Cytosolic Acetyl-Coenzyme A Molecular Cell
      Volume 53, Issue 5, 6 March 2014, Pages 710-725

  19. irina says:

    Dr. Mercola always picks up on Volter Longo’s accent! It is not nice after all. Dr. Mercola should appreciate his fellow Italian for his achievements and not to pick on something insignificant as pronunciation of some words. Interesting, Dr. Mercola never says anything about S. Panda that has the strongest accent of all to the point that in order to understand him you need to read subtitles( Ronda’s podcast) or Ben’s written subscript.

  20. Daniele says:

    The ice cream sounds awesome! Do you have recipes for it?

    1. Combine Dr Mercola's Autophagy Tea ingredients (listed in shownotes) with cacao and six egg yolks, a can of coconut milk, a little bit of collagen for the joints, add a little extra sweetener in that. Blend that and then put it in the freezer in a stainless steel bowl overnight.

      1. Jennifer says:

        He mentioned that Hydrogen Peroxide is BAD – what if you have a doc that wants to do IV Hydrogen Peroxide to get rid of a massive panel of IgG Viruses in an attempt to help with autoimmune disease?

        1. That is different. We are talking about oxidized peroxyl radicals in the body.

  21. Matt M. says:

    Hey Ben, around the 29 minute mark you bring up that H.I.I.T. in very short spurts could be effective while in a lightly fasted state. Is this one of those times where you fast from dinner till lunch around 1130 the next day and not eat again till after my workout around 1630? At which case I do the H.I.I.T. before the weights and also what would you recommend for the H.I I.T.?

    1. Here's a good resource from Dr Mercola:

  22. Dave says:

    A question about Dr Mercola’s proposed eating/fasting protocol. I can understand how it would help address compliance and reduce burden on detox pathways. The part that puzzles me is that I’m pretty sure Valter says that autophagy doesn’t really pick up until day 4 of FMD, therefore it would seem this protocol would negatively impact autophagy. Any thoughts resolving this apparent discrepancy?

    1. According to Dr Satchin Panda, mild autophagy begins around 12 hours fasted. Obviously you would get more and more as time went along… However, its the ketotic and low calorie nature of the refeed as your body will remain in ketosis, down-regulate mTor, etc. despite technically breaking the fast, while delivering nutrients to help stimulate recovery.


    I do the same thing as you do with the ice cream but I make a whipped cream with coconut cream and put all my powders in it and then put in my coffee as my treat. I do same with whipping cream on the days I do dairy.

  24. Mark says:

    Is black coffee still ok to drink on fasting days?

    1. Yes, it will not spike insulin/kick you out of ketosis and caffeine helps with brown fat mobilization.

  25. Michael Harding says:

    Hi, this may be a really stupid question but I feel compelled to ask anyway. Is water the best liquid to use when mixing all of the ingredients from the “autogaphy tea”?

    1. I'd recommend water.

  26. Robin says:

    HI Ben

    Does one drink the tea right before bed? IF so, isn’t that breaking the fast? Also, does Mercola recommend a 24 hour fast 1-2x/week? If so, would one take aminos or other supplements during that time?


    1. Intermittent Fast daily (12-18 hrs approx) then do the Keto Fast 2x's/wk. The tea can be the last thing you consume before starting your nightly fast. The Aminos would make a great vegan protein source during the low calorie fasting days.

  27. Leland Ave says:

    How do I get 300-500 calories from protein and not get BCCs?

    – Store bought bone broth would have BCCs, but I guess the ratios make it okay?

    – Collagen? And the point of the collagen is to help with detox not to stave off muscle loss should I also be training.

    – Home made bone broth is hard to figure the macros and calories of. My chicken broth always has fat in it.

    – Essential aminos – this could be like 150g of aminos. That’s a lot, no?

    1. Bone Broth most prominently features the amino acids arginine, glycine, proline and glutamine, and has negligible BCAAs. Essential Amino Acids with relatively low amounts of BCAAs are also acceptable.

      1. David Odell says:

        How do you get 500 calories from Bone broth?

        1. I wasn't suggesting that be the only source, just giving an example… You can also use collagen protein, vegan based protein (like pea protein), Essential Amino Acids (though not calorically dense)… Also Dr Mercola said primarily protein, so some healthy fats and non-insulinogenic plants should be fine too.

          1. Rob says:

            Jason Fung says protein breaks your fast and stops autophagy cold.

            Like 23-27min in this podcast

            I’m confused.

          2. This is a bigger issue if you're consuming animal-based protein, as it's higher in BCAAs. In large amounts they can create an insulinogenic response which mitigates the benefits of fast/ketosis. Dr Fung mainly advocates for complete calorie restriction fasting, but if you are going to consume something, you would again want to opt for something non-insulinogenic like C8 oil, grassfed butter/ghee, etc.

          3. I discussed this with Jason

    2. They key is BCAA quantity. As long as you have only a few grams you will not stimulate mTOR. Bone broot/collagen are very low in BCAA and high in glycine and proline hydroxyproline. It is KEY though to ONLY use organic grass fed collagen or bone broth as glyphosate will concentrate very high levels in connective tissue of CAFO animals. Most products on the market, even many best selling ones, are loaded with glyphosate

  28. Rich says:

    Hi Ben,

    You said you are not taking nicotinamide riboside anymore. So you are officially off the NR bandwagon? Reason being?

    1. I'm still getting it from Dr. Mercola's autophagy tea, and I also do an average of one monthly injection and use the NAD patches

      1. Rich says:

        I know he has made the podcast rounds, but it would be great for you to interview Dr. Sinclair to discuss NMN and NAD.

  29. Jsn says:

    Weight loss… This is always touted as a good thing. Like when he says every time I do this this I lose 3-5 lbs. Many of us want to be healthy and take advantage of these benifits but don’t really have any weight to lose. Can we get a segment on how to do some of these things without losing weight? Like if I’m on a 2500 calorie diet just to maintain 135 what are some methods I could employ? 4k calories on refeed days? I can’t imagine that’s healthy and I have to think that many of your listeners are like me, already fit, already highly active, hard gainers as it is that can’t sustain weight loss. Are there any resources you can point to for us?

    1. Not all strategies are best for all people. Yes you would want a bigger refeed the other days. Intermittent Fasting (approx 12-18hrs) still has great benefits for autophagy, insulin regulation, etc. and could be more sustainable for you.

  30. Berkley says:

    Is the transcript for this available?

  31. p says:

    Ben, you need to move on from this topic.

  32. blake says:

    Do you have any evidence that the MTOR pathway has detrimental effects in humans?

    Or that a ketogenic diet is beneficial for longevity?

    It seems the same circle of health bloggers which appear in the “do not trust” lists keep prattling on about insulin, autophagy, ketosis, sugar, “type 3 diabetes” and fasting; based purely on mechanistic data combined with speculation.

    These 2 have both gone completely off the deep end in regards to credibility and evidence-based recommendations.

    1. John P says:

      “It seems the same circle of health bloggers which appear in the ‘do not trust’ lists ”

      Who gets to make those lists, though? And why do plant-based/vegan docs never make those lists–even though they do plenty of cherry-picking (see “What the Health” for example). There’s plenty of evidence that fasting and calorie reduction are beneficial. Mercola is giving his own version which may or may not be one of the better ones. He’s not one of my favorites, BTW. He pushes too many supplements and has a few weird ideas. But that doesn’t mean he’s wrong about everything.

    2. You can search for all of these things at PubMed… Check this out: and

    3. Rather than going by your gut feelings why don’t you invest a few hours or even better a few hundred hours like many of us have and review the appropriate Pub Med literature. Strongly suspect you will be singing a different tune.

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