Dear Mark: Ketosis and Cancer, Probiotic Dosing Patterns

For today’s edition of Dear Mark, I’m answering two questions. First up, is the ketogenic diet an effective cancer treatment? There’s a lot of hype in the media and online world about ketosis, but what does the research really say? Then, I discuss a few different probiotic dosing patterns. Should you take them every day? Is there a benefit to switching brands from time to time? Should you ever megadose probiotics? How did ancient and preindustrial people “supplement” probiotics?

Let’s go:

Hi Mark,

I’ve read a few studies about the use of a ketogenic diet as an effective treatment option for cancer. Basically, the studies purport that cancer cannot survive on ketones, but instead require glucose to proliferate. I.e., eliminate glucose, starve cancer cells. I was hoping to get your opinion on this – can tumors really be subdued with strict ketosis?



First I’ll point out that there are over a hundred types of cancer. What’s good (or bad) for one type might not be good for the next type. So when we discuss the effects of ketosis on cancer, we have to be extremely specific. And above all, we must remember that none of this constitutes medical advice. I’m not qualified to give it and the science is extremely preliminary.

With that said, several lines of evidence have lead many researchers to conclude that ketogenic diets may have efficacy in cancer treatments.

But just because high blood sugar seems to exacerbate cancer progression doesn’t mean ketosis will halt or even slow it. Does it?

Numerous animal and in vitro studies have found that ketogenic diets or ketone administration can improve survivability, slow tumor growth, increase tumor cell death, and improve the efficacy of traditional cancer therapies. One study found that injecting ketones into chow-fed mice increased tumor growth. Interesting, but injected ketones on top of a non-ketogenic lab chow diet isn’t analogous to how ketogenic dieters produce ketones. I’m not sure we can draw any conclusions from that one.

There have been a few human studies, mostly testing the effects of ketogenic diets on brain cancer patients. The evidence is mixed.

In a group of 16 advanced cancer patients, ketogenic dieting improved quality of life, including emotional processing, in those who could tolerate the diet. In a recent pair of case studies, glioma patients showed tumor progression on a ketogenic diet. The tumors actually began producing enzymes necessary to metabolize ketones, suggesting that some gliomas can adapt to ketogenic diets and switch over to the new fuel source. In addition to reporting the case studies, researchers also reviewed the human keto diet/brain cancer literature as a whole, concluding that some brain cancer patients respond well to ketosis while others see no benefit. Those who do benefit enjoy slowed tumor progression. That said, only one of the human case studies covered in the review used ketosis as a monotherapy; all others used keto in conjunction with more traditional cancer therapies (radiation, chemotherapy).

As for why rodent cancer patients do so well on keto, they’re usually genetically homogenous lab creations, not “wild-type.” Their tumors all respond more or less identically to various inputs, whether they be radiation, supplements, or ketogenic diets. Humans are wild-type, and tumors from different humans have different degrees of ketone metabolism and thus different responses to ketosis. Those whose tumors express fewer ketolytic enzymes will likely fare better on ketogenic diets than patients whose tumors express more ketone-metabolizing enzymes.

Still, when used as an adjunct to cancer therapy, ketogenic diets appear to be safe and free of serious side effects. If I were diagnosed with a brain cancer, I’d probably try a strict ketgeonic diet. It’s safe, and very well might improve my prognosis, quality of life, and response to treatment. In other words, ketogenic diets under the supervision of your oncologist probably can’t hurt to try. But don’t assume you can “just go keto” and forego all other treatments.

The jury’s still out, but I expect we’ll get some real answers in the near future.

Hi Mark,

Any thoughts on the benefits/drawbacks of cycling probiotic intake? Either by cycling on-periods and off-periods…or by switching to new strains after a period of time?

Thanks in advance,


To my knowledge (and I try to stay apprised of the research in this particular area), researchers haven’t yet formally examined the question.

In the absence of hard data, I look to traditional and ancestral precedent. Not as the final word, but a starting point for informed speculation. So let’s speculate.

If the best-studied extant tribe of hunter gatherers — the Hadza — are any indication, it followed a steady pattern punctuated with mega doses. Mega-doses? The largest acute exposures to exogenous bacteria occur when the Hadza make a kill. To wash off the blood and bits of viscera caked on their hands, they use fistfuls of partially-digested plant matter from the still-warm guts as hand scrubbers. Not soap and water. Not hand sanitizer. Stomach sauerkraut teeming with microbes.

Then, they slice the raw stomach into bite-size pieces and eat it on the spot. No cooking, no parboiling to remove contaminants. Straight up stomach sashimi.

And finally, after removing as much fecal matter from the colon as possible, they toss it on open flames to cook for a few minutes. Charred on the outside but mostly raw along the bacteria-rich inner walls, the colon is sliced and served. That’s a literal megadose of colonic bacteria.

Underlying those megadoses was a consistent, close relationship to the microbial world around them. Extended breastfeeding. Co-sleeping with your entire family. Digging for tubers, gathering honey, hunting. That’s the backdrop against which they interacted, lived, handled: the dirt, dust, bugs, plants, animals, and each other, all teeming with microbes.

If hunter-gatherers obtain their “probiotics” passively by residing in the natural, de-sterilized environment, others cultures get theirs via fermented foods.

In Korea, kimchi is a staple food eaten with every meal.

Japan has soy sauce, natto, miso, and other interesting items.

In much of the Mid East, India, the Mediterranean nations, Russia, and Eastern Europe, fermented dairy (yogurt, cheese, or kefir) is eaten or drunk every day.

Western Europeans have their cheese habit.

The Mongols conquered the world on fermented mare’s milk.

For the most part, exposure to probiotic happened daily for most people throughout history, whether via fermented food staples or passive contact with environmental microbes, often both. I can’t think of anyone more divorced from their natural microbe-replete environment than modern Westerners. We think kimchi is “smelly.” We buy pickles soaked in vinegar, not lacto-fermented brine. We live in a world of hand sanitizer, antibiotics, draconian hand washing measures, cupboards full of antimicrobial chemicals. We spend our lives almost entirely indoors. We often need probiotic supplements supplements just to be normal. (And because I personally wanted the best and it didn’t exist in the marketplace, I created Primal Flora.)

Now, if you’re the type to demand randomized clinical trials for every decision you make, stick to daily “normal” dosing. Every probiotic study I’ve seen uses 1 to 2 pills a day. That’s the only concrete data we have to go on, and we know that works if the strains being used are useful for the effect being sought. Could cycling work better? Perhaps, but I haven’t seen any evidence and simply eating a variety of fermented foods (each with its own stable of microbes) is a kind of cycling. Might megadoses speed up colonization and realization of health benefits? I wouldn’t be surprised.

As I see it, there’s precedent for both steady intake of probiotics and infrequent megadoses. Probably both at once. Less so if you’re eating fermented food regularly.

Thanks for reading, everyone. Take care and have a great rest of the week. As always, I’d love to get your input on today’s questions!

TAGS:  dear mark, Keto

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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25 thoughts on “Dear Mark: Ketosis and Cancer, Probiotic Dosing Patterns”

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  1. Is it true that we should not take probiotics if we have SIBO, that the bacteria risk colonizing our small intestine?

    I feel like it’s counter intuitive with everything you said here, but then, hunter gatherers don’t normally get SIBO I guess.

    1. I have SIBO and cannot tolerate even small amounts of probiotics without rediculous amounts of brain fog. I’ve been using resistant starch, specifically 2T potato starch, a few times a day and I can definitely tell a difference. Soil based ones every once in a while, but not ones with lactobacilli and bafidobacteria. Everything I’ve read up until this article the other day said those are the specifically overgrown ones in the small intestine.

      Maybe it’s a dosage thing. I’d love to hear Mark’s thoughts on this!

      1. I’m exactly like you, yogourt or soy based yogourt give me horrible migraines but I’m ok taking Primal Flora. It’s been a while now that I suspect I have SIBO but it seems impossible to self treat really.

        1. I totally empathize with self-treating.

          I guess it really depends on if the small intestine is actually mostly sterile (which seems unlikely). Resistant starch, balancing out my hormones, and supporting detox pathways has helped me tremendously, but not entirely.

          The comments section in that article I mentioned actually has some interesting detailed advice from the author. She recommends adding in certain strains in very small dosages gradually in stages.
          Definitely might give it a try one day!

          Good luck in your healing. Just thought I’d mention it because I know how hard SIBO is to deal with.

      2. “I don’t recommend spore forming soil probiotics either, as these have the ability to turn pathogenic.”

        So I should not take Primal Flora according to her. And here I was happy to finally have found a probiotic I can take without bad side-effects. That’s the biggest problem with self-treating, the amount of contradictory information you will find on the internet is overwhelming!

  2. I make alternately homemade sauerkraut or a lacto-fermented garlic radish pickle in mason jars. They are really good on salad or a topping for meat. I find that I have better BMs when I make this a regular part of my diet

  3. Investigations have moved beyond just KD.

    Non-Toxic Metabolic Management of Metastatic Cancer in VM Mice: Novel Combination of Ketogenic Diet, Ketone Supplementation, and Hyperbaric Oxygen Therapy

    And with any trials, rodent or human, involving a reported ketogenic diet, the makeup of the KD must be put under a microscope. Most lab rodent KDs are junk (basically Crisco). D’Agostino had to have a KD custom formulated. And don’t get me started on alleged placebos in typical studies …

  4. Japanese pickles are really easy and a good way to use an overabundance of garden cucumbers. Just peel and slice them, then layer into a bowl. Salt each layer according to preference. (Cukes can take a lot of salt, so don’t be afraid to use quite a bit.) Set a snug-fitting plate inside the bowl on top of the layered cucumbers and put a weight on top of the plate. (I use a 48 oz. can of tomatoes.) Refrigerate for a few days, pouring off the water as it accumulates. The longer you refrigerate, the crunchier the pickles will become.

    These pickles will likely be more heavily fermented if you leave them on the counter, but they won’t get as crisp.

  5. Thanks for such a balanced reply to the cancer & ketosis question. For anyone who’s interested in delving into the science behind “the metabolic theory of cancer” (as opposed to the genetic mutation theory), I’ve been running a series on my blog for a while. I’ve covered a lot of the biochemistry — in layperson-friendly ways — ultimately laying the groundwork to build the case for why ketogenic diets should be much more utilized as adjunct therapy than they are now. And let me stress that: I don’t think ketogenic diets, by themselves, are enough. But they should be implemented more often than they are as a *part* of the multi-pronged strategy. They have helped a lot of people have a better quality of life and tolerate the conventional treatments better. (Fewer debilitating side-effects, and they may also actually increase the efficacy of chemo drugs.) I think ketogenic diets would hold a great deal more promise for human cancer patients if they were implemented *immediately* upon diagnosis, rather than used as a last resort for people who are already in stage 4 metastatic illness. Sadly, the oncology world largely still fears ketogenic diets, and they are not exactly going around telling people that cancer cells are sugar junkies at the same time they’re encouraging these folks to down corn syrup-laden Ensure shakes just to keep weight on. It’s almost like, they hold back on even *mentioning* the ketogenic approach until someone is almost at death’s door, because it’s like, “Well, you’re not long for this world anyway; couldn’t hurt to try this crazy diet *now.*” Oy.

    Ketogenic diets are absolutely not miracle strategies for fighting cancer, but for goodness’ sake, they ought to at least be explored. Patients should be given the scientific rationale for trying them, so they can make an informed decision for themselves as to whether it’s something they want to try. At the very least, they should be educated as to the role of glucose as the preferred fuel for many cancers, so they can choose whether they’d prefer to stick with Ensure and ice cream, or maybe switch over to fatty pork chops.

    The blog series starts here, and each post contains a link at the end leading to the next one:

    The specific post people might be most interested in, regarding cancer cells’ affinity for glucose is this one:

    People can check out a lecture by Dr. Thomas Seyfried, one of the leading researchers in this area:

    The book that sparked my interest in this is Tripping Over the Truth, by Travis Christofferson. Absolutely fascinating stuff:

    1. Thanks for the link- I’m interested in this topic too. Also intermittent fasting reportedly helps reduce the dreadful nausea and vomiting associated with some types of chemo. Is there any supporting research for that, do you know?

  6. If I came down with cancer, I would do the things the doctor recommends … AND immediately enter long term ketosis. There doesn’t seem to be any downside to ketosis, it’s easy to do and has long term health benefits anyway.

    The only thing more effective, as far as I’ve read, is long term fasting, like sessions of 20 to 30 days.

      1. Book recommendations, not links. I’ve read quite a bit about a technique I hope never to use. I try to fast 24 hours once a week, that works for my schedule.

        “The Miracle of Fasting” by Paul Bragg is excellent. He was Jack LaLane’s teacher by the way. Paul Bragg’s message is very similar to the Primal Blueprint in a lot of ways.

        Three more books that I do not recall off hand at my local library. Do a search at your library, all the titles have “fasting” in them.

        The idea of fasting to beat cancer is really simple, your body starts looking around for material to burn as fuel, and anything it considers useless (like cancer cells) gets disassembled and burned.

  7. For cancer I’m thinking of a 20 day fast followed by a healthy dose of eating raw stomach contents.

  8. None of us know whether our digestive system enables revival of those dried bacteria, packaged in the probiotic capsule. Imagine a situation, where years of junk food, culinary abuse, binging, etc., leads to such an imbalaced gut, that the supplemented micro-organisms prefer not to wake up.
    Therefore, if you want to colonize your gut in “safe mode”, start by eating yogurt, made with the capsule’s content. This way you also benefit a few orders of magnitude more bacteria.
    If you like thick yogurt, don’t forget to heat the milk. Add the bacteria once cooled.

  9. I enjoyed your article on “Probiotics”. There are so many probiotics, in stores today, each to help with some ailment, digestion, gas, bloating, and more. It would make more sense getting them from a variety of quality foods. Isn’t that what doctors tell us, to do to obtain our vitamins and minerals?

  10. This is anecdotal of course, but when I was diagnosed with breast cancer in March of 2014, I immediately went on a ketogenic diet. In fact, as soon as I found the lump I stopped eating any carbs but leafy greens and veggies. I was fortunate to have a very fast turnaround-found the lump on 3/14 and had the surgery on 3/31. I had a special test run by my surgeon-we sent a 1.5 cm2 sample to Rational Theraputics in California to test for chemo sensitivity. They usually test 10-12 different chemo agents/combinations but were only able to run 4 on my sample. The reason? The tumor cells were largely necrotic (dead). The tumor was very fast growing and it is possible that it outstripped its blood supply or that might have been a contributing factor, but I think that depriving the very fast growing cells of fuel was a factor. It certainly didn’t hurt. Plus there was the added benefit of feeling like I was in control of something. Getting diagnosed with cancer is scary and suddenly you have little control over what is happening. But I could control what went into my mouth and I did. I am approaching one year following the last chemo treatment (10/31/14) and so far, so good. I still try to stick to low carb but I’m not doing the full blown keto diet I was on at first.

  11. I’ve been following the keto/cancer thing for a while now, so a few comments for those that want to dig further… is one of the best places to start for a complete inventory of thinking and links on the topic of keto-related cancer treatment…
    …however, diet and lifestyle seem likely to be much more effective for preventing cancer in the first place than stopping it once it has progressed to a late stage. The human trails so far as I know have all been in people with very late stage cancer, however populations with primal-style (not necessarily keto) diets tend to be low in cancer.
    Paul Jaminet’s cancer series at is also interesting reading, and he points out that some aspects of very low-carb (e.g. under 60 or so net carbs per day) may likely promote cancer by weakening the immune system. This seems to be loosely supported by a variety of ultra-low-carb and populations that had very good health but were not particularly long-lived. The solution seems to be to go a bit higher carb (i.e. 100-150 grams net carb per day) and perhaps go cyclically keto, from time to time by lowering the carbs/protein a bit and using coconut oil/MCT oil/exogenous ketones. Ketones apparently may have an anti-cancer gene expression aspect. Paul also raises the point that in some cases, what is anti-cancer for someone who does not have advanced cancer (e.g. some nutrients) , may actually support cancer once it is at a later stage, so that is something to look into closely.
    Once of the advantages to ketones for brain cancer is that they cross the blood brain barrier, which is one of the problems with anti-cancer drugs, and it seems that of the anecdotal reports of people with cancer remission on a keto program, most of them seem to be brain cancer cases, which is not to say it won’t be helpful elsewhere, but still interesting.

  12. Your gut bacteria “population” is also impacted by the level of fermentable fibre that your “feed” them each day, i.e., Vegetable matter that your eating each day.

  13. Nice article Mark. I’ve been interested in glioblastomas for a while and I’m not totally surprised that one of the patients in the Schwartz et al (2015) paper showed continued progression of his tumor, regardless of whether he expressed ketolytic enzymes. Ketosis was achieved via a combination of calorie restriction (good) and Ketocal (dubious). What I could find on Ketocal indicates that it is composed of over 25% trans-fats and 12% polyunsaturated fats. Sure, these likely convert to ketones, but I’m not sure the ketones can overcome the negative effects these substances have on the mitochondria, which is where the ketones do their “magic.” I mean, 25% trans-fat? I guess J.M. Smucker found a way of disposing of his Crisco. Cheers.

  14. Thank you to the readers for their thoughtful questions and to you Mark (and your diligent employees), for your attention to them. I must say, I truly appreciate your approach to presenting the information that you find on various research (and have for more than three years now); the efforts you make to express: what you believe results point to; that not all science is good and not all is applicable across the entire board; if results or conclusion drawn in articles appear viable or not; your personal opinions or your beliefs; and what conclusions we could infer, draw, or not come to at all are very helpful and very true to what it means to share information in a meaningful, informative, fair way. Examples:

    “What’s good (or bad) for one type might not be good for the next type. So when we discuss the effects of ketosis on cancer, we have to be extremely specific…”

    “Interesting, but injected ketones on top of a non-ketogenic lab chow diet isn’t analogous to how ketogenic dieters produce ketones. I’m not sure we can draw any conclusions from that one.”

    “Could cycling [of probiotics] work better? Perhaps, but I haven’t seen any evidence…”

    Mark, this is why I always come back to read your blog and recommend it to anyone I know who may listen. I hope you always remain inspired to do this. It inspires me to continue doing the same in my life with regard to any topic I discuss, both as someone with a science background and as someone with an interest in this area of health (at least as a hobby/health-seeker/spreader-of-what-I-believe-to-be-good-information). Thank you for all do. Please, please continue!