Dear Mark: What’s the Deal with Fiber?

Fruits and VegetablesLast week’s guest post from Konstantin Monastyrsky, author of Fiber Menacegenerated a lively, boisterous, and at times combative comment section. I use these descriptors in the best sense possible, mind you; debate is healthy and necessary, even – nay, especially – if it’s impassioned. So right off the bat, I want to thank everyone who wrote in. I also want to thank Konstantin, whose views on fiber forced me to reconsider my own way back when I first encountered him over five years ago. Without his input last week, we wouldn’t be having this discussion, and many people would still be sitting on whatever side of the fiber fence they prefer, never even considering that another side exists. I know I might still be catching up if I’d never read his book all those years.

Many of you asked whether I endorsed the views espoused in the guest post. You wondered whether I’d shifted my stance on the Big Ass Salad. You wanted my take on the whole fiber thing, basically. So without further ado, let’s discuss fiber.

It’s often said that fiber is indigestible, that it serves no nutritive purpose – and that’s partially true. Humans can’t digest fiber. Our digestive enzymes and endogenous pancreatic secretions simply have no effect on roughage. Our gut flora, though? Those trillions of “foreign” cells residing along our digestive tract that actually outnumber our native human cells? To those guys, certain types of fiber are food to be fermented, or digested. That we feed our gut flora these prebiotic fibers is important for three main reasons:

1. Because the health (and composition) of the gut flora helps determine the health of the human host (that’s us!). It’s difficult to name a physiological function or health parameter that is not impacted by the gut microbiome, including but not limited to digestive, cognitive, immune, emotional, psychological, metabolic, and liver health. Our microbiota depend on fermentable fibers for food. It’s not clear what exactly constitutes “healthy gut flora,” and we’re still teasing out exactly how it affects the various physiological functions, but we know we need them and we know they need to eat something to even have a chance at helping us.

2. Because the short chain fatty acids that are byproducts of fiber fermentation, including butyrate, propionate, and acetate, improve our health in many ways. Butyrate in particular has been shown to have beneficial effects on insulin sensitivitycolonic transportinflammation, and symptoms of Crohn’s disease. It’s also the preferred fuel source for our native colonic cells. Basically, without enough butyrate (and, by extension, fermentable prebiotic fiber to make it), our colons don’t work as well as they should. This can lead to digestive impairments and perhaps even cancer. Mucin-degrading bacteria predominate in colorectal cancer patients, for example, while butyrate-producing bacteria rule the roost in healthy patients without cancer. Populations with lower rates of colorectal cancer also tend to have higher levels of butyratePropionate is helpful, too, though not to the extent of butyrate.

3. Because by feeding and bolstering the populations of “good bacteria,” we reduce the amount of available real estate for “bad bacteria” to set up shop. Gut bacteria don’t just float around in there. They cling to surfaces, nooks, crannies, and crevasses. They’re impossibly small, but they do take up space. After antibiotic treatment where both good and bad gut flora are indiscriminately targeted and wiped out, pathogenic obesity-promoting bacteria take advantage of the open space. That’s a worst-case scenario, but it shows what can happen when the harmony of the gut is disturbed (whether by antibiotics or lack of fermentable fibers).

Overall, because the health of our gut community is inextricably tied to the health of our minds and bodies, I think attaining fermentable fiber through the fruits and vegetables we eat is incredibly important. Heck, even the only food that’s actually expressly “designed” to feed humans – breast milk – contains prebiotic compounds whose main purpose is to feed and cultivate healthy gut flora in infants, which suggests that the need for prebiotics is innate. Coprolite (read: ancient fossilized stool) studies certainly indicate that our ancestors may have consumed a significant amount of prebiotics, and we even have receptors and transporters built-in to handle and accept the butyrate produced from fermentable fiber. Or, if you want to say that humans haven’t evolved a dietary requirement for fiber, that’s fine. But we have evolved to rely on gut flora to help our bodies work best, and that gut flora has evolved to require a steady, varied source of fermentable, prebiotic fiber. That can’t be denied.

have been suspicious of fiber in the past, though. Like Konstantin, I’ve discussed the folly of loading up on the kind of fiber whose only purpose is to rend the intestinal walls, doing enough damage to induce mucus secretion which acts as lubricant. I’m talking about insoluble fiber, of course.

Insoluble fiber is a bulking agent. You know how weight lifters swear by whole milk and beef for adding mass? Insoluble fiber is like that, only for poop. It makes for extremely impressive toilet bowl displays and potentially expensive plumber fees, I’ll admit. And some people “need” to feel like they’ve done something down there. They like to take a peek after a bowel movement and let the distinct sensation of accomplishment wash over them. But for digestive health? I’m unconvinced, and there’s not much evidence in favor of it. Optimally, stool is made up of mostly water and bacteria – not undigested food.

The health claims just don’t add up.

For one, insoluble fiber doesn’t ferment very well. That’s why neither we nor our gut microbes can digest, say, cellulose-rich grass – we don’t have the hardware, and neither do our gut flora. No fermentation, no short chain fatty acid production.

How about constipation? Bulking up your stool is supposed to improve symptoms of constipation, right? That’s why almost every doctor will tell you to “eat more fiber” upon hearing that you’re constipated. It’s gotta be evidence-based advice! Well, the actual evidence is rather weak. A recent meta-analysis concluded that while increasing dietary fiber does increase the frequency of bowel movements, it does nothing for stool consistency, treatment success, laxative use, and painful defecation. So it will make you poop more often, sure, but each bowel movement is going to hurt and you’re still going to need laxatives to do it. Another recent study found that stopping or reducing dietary fiber intake reduced constipation.

Or cancer? One recent study compared the fiber intakes and gut flora composition of advanced colorectal cancer patients to healthy controls. Healthy controls who ate high-fiber tended to have more butyrate-producing microbes than low-fiber healthy controls and high-fiber cancer patients, suggesting that it’s not “fiber” that protects against cancer but “fermentable fiber.” The cancer patients who ate high-fiber were likely eating insoluble, cereal-based fiber, which was not protective. This jibes with an older study’s results: while both fruit and vegetable fiber were associated with lower risks of cancer, cereal fiber – which is mostly insoluble – was associated with a slightly higher risk. Another study found similarly protective links between fruit and vegetable fiber and stomach cancer, but not grain fiber.

If you desperately need to execute a double decker at the home of a sworn enemy, load up on insoluble fiber beforehand. Otherwise, stick to what insoluble fiber you’ll get as a byproduct of eating real fruits and vegetables.

How many fruits and vegetables should I eat, you might be wondering? And does that mean soluble, fermentable fiber, and lots of it, is fair game?

It depends. I know that’s not a sexy, easy answer, but it’s the right one. Allow me to explain.

The Sub-Saharan farmer who’s spent his life handling and milking goats, picking up and distributing manure, working the fields, plunging his bare hands into fresh loamy soil to plant a seed or pull a weed, taking his meals with soil still underneath his fingernails, eating lots of fiber-rich vegetation (often without washing it), and encountering not a single dose of antibiotics is going to have a more robust, varied gut microbiome and greater capacity to handle fiber than the suburban pencil pusher (perhaps that term needs updating – let’s go with keyboard rattler or desk jockey) who’s spent his childhood mostly indoors wearing a perma-sheen of hand sanitizer and sunscreen while eating a diet of peanut butter and jelly on white bread, mac and cheese, hot dogs, and pizza, and his later years wracked by chronic low level stress that disrupts his gut flora and alters his digestion.

Should you fear fruits and vegetables because of the fiber? Has your modern upbringing ruined your digestive capability forever? No, I don’t think so. It may have temporarily impaired your ability to handle fermentable fibers – increasing numbers of people are reporting trouble with the class of fermentable carbohydrates known as FODMAPs (check the FODMAP list at this PDF) largely because they don’t have the right levels/populations of gut flora – but it isn’t permanent. You just need to be aware of the complex, delicate interplay between the food fiber we eat, the composition and health of our gut flora, and our digestion. You should pay attention to your own digestion and how fiber affects it. You should introduce foods rich in soluble, fermentable fiber gradually and even cautiously. Allow time for your gut flora to adjust to the new food source. Expect flatulence.

But you should definitely introduce them.

Eventually, you’ll be able to fish a sample out of the toilet, snap a shot of it with your iPhone camera, and have your entire gut microbiome analyzed on the spot, complete with dietary fiber recommendations for optimal butyrate production and minimal flatulence, but that’s a long while off. Scientists are still figuring out which gut flora are best, which species are good and which are bad, what kind of fiber source they like, and how often and how much we should feed them. In other words, we’ve reached the stage of knowing enough to know that we know very little. In the meantime, we know “gut flora are important.” We have vague ideas of which populations are “good” based on correlative studies that link certain species with diseases. We know we need gut flora because of their endless interactions with the host, and that they need food. We know that the plants (and breast milk) we eat provide that food.

And that’s about it.

It’s enough to get started, though. I’d say between 75 and 100 grams of carbs from mostly vegetables and some fruits, plus the occasional emphasis on plants particularly heavy on the prebiotic fiber – stuff like raw onion and garlic, leeks, jerusalem artichokes, dandelion greens, raw plantains and green bananas – should provide sufficient food for your gut. If you have too much, you’ll know it.

Oh, and the Big Ass Salad is definitely here to stay.

That’s what I’ve got, folks. What say you?

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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100 thoughts on “Dear Mark: What’s the Deal with Fiber?”

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  1. I think everyone should look at their poo after passing it. It really does say a lot about the health of your gut.

      1. Yeah I like rating my own poo, rating other peoples poo quickly begins to turn my stomach. Especially after I saw one titled: “After three days of taco bell”.

    1. Yep, to deny that our gut flora need proper care and feeding puts one in the dark ages.

      The only problem I have with your post, Mark, are the terms ‘soluble’ and ‘insoluble’ as descriptors for ‘fermentable’ and ‘non-fermentable’. There is soluble fiber that are non-fermentable, and insoluble fiber that is fermentable. Also, some soluble, fermentable fiber is targeted more by pathogenic bacteria.

      If we look at the FODMAPs, some of them are good ‘gut-bug’ food, and some are not.

      Better descriptors for fiber recommendations would probably be ‘bifidogenic’, ‘butyrogenic’, or just ‘prebiotic’ fiber. These terms all relate to how beneficial gut microbes react to the food source.

      Termed as I described, it would be clearer to see that the most important fibers probably are inulin, pectin, oligosaccharides, gums, mucins, and resistant starch.

      Your recommendation of: “stuff like raw onion and garlic, leeks, jerusalem artichokes, dandelion greens, raw plantains and green bananas” gets us inulin and resistant starch. I’d like to give a shout-out here for properly prepared (fermented) legumes, raw potato and tapioca starch, parbroiled/converted rice, and…a daily apple (for it’s pectin content!)

      1. I would be grateful for more information on types of fiber. Big Ass Salads worked for me for a while, but then I got very constipated- possibly too much spinach & arugula. I tried eating onions for inulin, which if anything made things worse, and probiotics, which seemed have no effect. What acually did help were potatoes- white and yellow, not sweet. These days I avoid salads, eat vegetables cooked in broth, stone fruits and berries plus a potato every day or two. What is it about the potatoes?

        1. the resistant starch, your large intestine does a lot of good with it.

        2. I’m not sure we are actually correct on the terms of what constipation and other forms and speeds of digestition are.

          Who knows whether we and our primal ancestors are hard-wired to digest and poop within a certain timeframe and with a specific result? This probably varies from the exact types of food you eat, how much coffee/tea you had, whether you have regular meal times or not, etc.

          So, I think it’s hard to find an ideal digestition window as a sort of standard or “benchmark” in the first place which is then subject to individual eating, drinking and lifestyle habits.

          Thanks for sharing your latest advice and thoughts on the subject, Mark!

        3. Just my 2-cents: What is normal? My cats used to poo large, smelly droppings twice a day. They had a host of health issues. I put them on a 95% meat no grain diet and it all cleared up. They are spectacularly healthy. Now they only poo very small, non-smelly, hard poos once every 2 days (I have to clean the box 🙂 Now, I am aware that cats aren’t people and vice versa. Nor am I saying we don’t need fiber. I am simply pointing out that who knows what healthy poop looks like? Sounds like CW to me.

          Also, potato starch sounds like processed food. I’m not a big fan…

          Of course I’m no expert, but I truly believe good health comes from whole foods.

        4. Oh, and another thing, it is possible that when we poo less, we may not be constipated, we may be using most of our food and not have so many waste products left.

      2. *Raw* potato? That sounds considerably less tasty than not-raw potato…

        1. I think that was meant to mean raw potato starch and raw tapioca starch. A lot of people are using those to increase their intake of resistant starch without all the calories.

          There is a complete list of resistant starch contents in foods here:

    2. Yeah…my to do list is already to long. I think I’ll pass. (Tee hee)

  2. Once again you have provided a great deal of food for thought as well as the rest of the body!

  3. Execute a double decker at an enemies house! I almost #@#@ my pants when I read that. Great scoop on the poop.

  4. Yep, to deny that our gut flora need proper care and feeding puts one in the dark ages.

    The only problem I have with your post, Mark, are the terms ‘soluble’ and ‘insoluble’ as descriptors for ‘fermentable’ and ‘non-fermentable’. There is soluble fiber that are non-fermentable, and insoluble fiber that is fermentable. Also, some soluble, fermentable fiber is targeted more by pathogenic bacteria.

    If we look at the FODMAPs, some of them are good ‘gut-bug’ food, and some are not.

    Better descriptors for fiber recommendations would probably be ‘bifidogenic’, ‘butyrogenic’, or just ‘prebiotic’ fiber. These terms all relate to how beneficial gut microbes react to the food source.

    Termed as I described, it would be clearer to see that the most important fibers probably are inulin, pectin, oligosaccharides, gums, mucins, and resistant starch.

    Your recommendation of: “stuff like raw onion and garlic, leeks, jerusalem artichokes, dandelion greens, raw plantains and green bananas” gets us inulin and resistant starch. I’d like to give a shout-out here for properly prepared (fermented) legumes, raw potato and tapioca starch, parbroiled/converted rice, and…a daily apple — see

    1. And what about beta-glucans? Aren’t they a type of fermentable fiber? Oh how I wish someone would create a list of the various fermentable fibers and good dietary sources!

      Here, I’ll start one:

      Beta-glucans: mushrooms, barley and oat bran (Oops, did I say a bad word? I’m new to this Paleo movement and just starting to learn my way around…)

  5. Whew!! Thank goodness the Big Ass Salad can stay. That’s what I called them way before I read The Primal Blueprint, so I was very happy when I read that’s what Mark eats as well. I think I was almost primal before I knew what primal was. Thank you, Mark! Great read.

  6. Bottom line: “It’s not clear what exactly constitutes “healthy gut flora” “…

  7. I still don’t think Konstanin was recommending that we not eat fiber last week—just that we not go crazy trying to *make* it part of our diet. Eating normal amounts of fruits and vegetables is a healthy thing to do, and a reasonable amount of prebiotic fiber is just another benefit. I don’t think anyone said otherwise.

    1. +1 agreed

      I also think Mark’s tone here is more sardonic than Monastyrsky’s was. And I love it when Mark writes posts like this!

  8. execute a double decker at the home of a sworn enemy

    Am I the only one thinking Burger King here?

  9. In the spirit of promoting debate, can Konstantin chime in here to tell us whether he agrees or disagrees with Mark’s post… ?

  10. So basically fiber is necessary for those of us that poop our pants because our stool is too loose. Hopefully the fiber will build up the gut flora necessary to thicken up that stool.

  11. Just wanted to add that some lists of FODMAPs foods to avoid list lettuce as problematic for some people–as it definitely is for me. Let the N=1 guide you on that one, I guess.

    1. I concur! I love – LOVE – broccoli and cabbage, but cooked or raw, I get terrible gas and sometimes stomach pains/issues. Sometimes some people just don’t handle some foods well. Believe me, I wish I could.

  12. And I know this is against the rules, but I think Mark needs to be nominated for quote of the week for his “double-decker” statement. Almost laughed out a double-decker in my chonies when I read that!

    1. Mark, you HAVE to give yourself comment of the week, even though it was in your article. “Execute a double decker…..” Brilliant.

  13. Due to several oral surgeries and bone grafts this summer, I’ve had to take several rounds of antibiotics. Hated to do it but I had some infections that had to be dealt with. I eat primal and no junk food, but I’m sure my gut microbiome got zapped.

    What do I eat to help repopulate it with the “good guys”? I do take a high powered probiotic. But RAW onions for prebiotic? Can’t handle them raw. Is cooked ok?
    Thanks for any suggestions!

    1. Obviously a probiotic is a good start. But if you have a clean water source and access to your own garden or a farmers market where no pesticides and such are used… try eating a few ground plants without washing them. Sweet potatoes, onions, garlic, carrots… or things growing on the ground like squash, etc. Their contact with the ground will expose you to more microbes and micro-organisms than most probiotics can provide. Pick off the big stuff… wipe ’em down… even cook them if you want. But skip the whole washing them part. That said… only do this where you know you have a good clean soil free of pesticides and junk and with a known, clean water supply to the garden. Personally, I wash everything I buy at the store, but I wash nothing that I grow in my own garden. We also have a farmer’s market nearby and I’ve chatted with one farmer who uses no pesticides… he doesn’t even fertilize beyond tilling rotten veggies and stalks back into the ground. And he also doesn’t wash his fruits and veggies. They go from the ground to crates in his truck to my mouth.

    2. Agree with Andrew: eat *cide-free, poison-free dirt. You could also get some by taking a walk in the woods with a small container. As long as you aren’t crunching grit (bad for teeth), go ahead and eat with slightly dirty hands or even lightly season your food with dirt. Use your own judgement on sources, frequency, and amounts.

      To follow up on that, for some reason, bacteria (and viruses, and perhaps single-cell protists as well) are able to copy/incorporate some of the DNA of other species they come into contact with. This is why you can, for example, gain the ability to digest chitin by eating shrimp tails or insects. Cooking food that you are using as a probiotic still works because bacteria are able to copy (steal?) from dead cells or free-floating DNA. Besides, most everything dies in your stomach anyway.

      Also, fermented foods count as probiotics as far as I’m concerned, and are prebiotics pretty much by definition.

      1. Depending where you live in the world would depend on advising on washing your home grown veggies.

  14. Having read last week’s post, my take away was that we shouldn’t be intentionally seeking out fiber as a supplement but to get it naturally from our food. The fact is, most of the carbs you consume will naturally come wrapped up in some form of fiber. An apple is a perfect example. If you take a dozen apples and squeeze them for their juice and drink it, you get sugary water in a form that affects insulin almost as much as eating a spoonful of processed sugar. But eat a single apple by biting into it and chewing it and you get some sugar that takes longer to be processed by the body due to the fiber its wrapped up in. Its better for your teeth (chewing) and the carbs (sugars) are processed more slowly and thus affect insulin in a better way. Do I want the ground wood pulp fillers (ie: sawdust) of processed junk food? Heck no. Do I want to take the husks that are normally considered trash surrounding the seed (ie: Metamucil) and to add it to a glass of water and drink it down? No way. But a salad full of spinach or an apple? That’s the way nature intended it to be consumed. And consider how grains used to be eaten at times. There was a time where you’d take the grain and crush and grind it in your hand and blow off the chaff (ie: the husk) and eat the seed/meat inside. In this sense, grains were a source of carbs wrapped in fiber, but it was the outside… the husk… that was discarded along the way. Its only our industrious companies that want to eek every last dollar out of every possible by-product that decided husks and sawdust and such should be ground up and processed and added to our foods as fillers and emulsifiers or sold as supplements.

  15. The line that got me giggling was “It makes for extremely impressive toilet bowl displays and potentially expensive plumber fees”. Thanks Mark!

  16. As for prebiotics — rejoice hazelnut lovers. Eat em raw and with the skins intact — the skins are loaded with prebiotics. They’re my fave so of course I’m a bit biased…

  17. Thank you for treating this subject with your usual care and circumspection.

  18. Fascinating article. My source of priobitics, in addition to veggies and fruits, is kefir. I sort of “make” myself take it due to worry about gut bacteria, especially when I slack off on my veggie intake. Perhaps I don’t really need to?

  19. Perfect. You pretty much described my upbringing, digestive health and how I solved it! Eliminating fiber, understanding which ones were not promoting health and slowly reintroducing new ones and to this day I can tolerate ‘normal’ levels of fiber.

  20. So, insoluble fiber like lettuce and cabbage is ok?

    After having gallbladder transplant I cannot tolerate starch at all, and most of the vegetables that have soluble fiber are starchy vegetables. Im confused..

  21. Does anyone have a child (or themselves) suffer from Encopresis? It’s basically chronic constipation where softer stools start pushing through and it looks like the child is soiling their pants, but they’re not doing it on purpose. My 9-year old has struggled with this for several years now, so this study intrigues me as I’m trying to find the “A-HA!” thing with him. We previously did the whole Miralax/Enema things as his Pediatrician originally prescribed but his condition wasn’t improving, the process was becoming traumatizing and after becoming Primal last year it was clear to me this could not be the best way to handle things. We’ve done mega-doses of probiotics with high fiber most recently (still not much success) but then I see this article and I feel like I’m back at square one that we’ve been doing EVERYthing wrong all along. Anyone else helped someone with chronic constipation through a lower fiber diet?

    1. Cooked rhubarb helped me when things were bad – though I needed some sugar with them. As do raw kiwi fruit – but no additional sugar needed.

    2. Definitely STOP with the insoluble fiber supplements IMHO. Make sure your child stays hydrated, I don’t mean slogging down water constantly, but a consistent amount between meals. You might also consider waiting to drink fluids until a half hour after meals. Of course, no soft drinks and NO milk. Maybe cut back on the strength of the probiotics for a while but make sure it has the right kinds and number of strains (some research will point you to those). The are also some homeopathic soil organism products out there, but you don’t want to hit him will too many things / changes at once, make incremental changes. Probably hard to find … if they even exist … a good holistic-based gastro-intestinal pediatrician.

    3. I suffered with constipation-related IBS since my early teens (I’m 42 now). I went on a cruise in 2001 and didn’t have a BM in 7 days. Trips were excruciating because all gut movement would come to a halt. Coffee and cigarettes are what I used to help me s**t.

      I did the low-fat, low-sugar, high-fiber, lots of healthy whole grains, veggies/fruit, etc. I dropped 10lbs and didn’t fix my IBS. The first thing I did was remove bread. That was the start. I literally started to empty out. My stools were looser than before. 3 weeks later I went Primal, removed all grains and within 6 weeks had a flat tummy for the first time in my life. I’m healing slowly. There is less there. It comes out easier (we’re talking straining to the point of bleeding – hopes this isn’t too much TMI). At least I assume I had IBS. The gastroenterologist who diagnosed me (when I was about 23. Took 4 years to get that diagnosis) didn’t want to do any “unnecessary tests” at the time so he made a guess based on my symptoms. Of course I went right along with him (BRAN DOES NOT HELP CONSTIPATION!! IT MAKES IT MUCH, MUCH WORSE!!)

      And I have Reactive Hypoglycemia so most fruit is out. Even berries will start the spikes/crashes and cravings.

      In my body less fiber means less pain and easier BMs. It means less toilet paper used. It means less bloat.

      I do have to admit that my gut loves sweet potatoes (don’t know about white ones. Never really liked them). I can tolerate the carrots and the squash and such – all lightly cooked. But not grains, not beans, and very few raw veggies.

      1. And I always look at my stool – my man thinks I’m gross but it is amazing what you can find out. I will even get a bit closer to it before flushing. That is why I no longer eat sunflower seeds and sesame seeds. My man’s stepdad was stumped as to how we manage to suck the nutrition out of corn and leave the shell intact. WTF!!! I had to tell him “you don’t”. I don’t think he believed me. If it shows up in the toilet looking exactly like it did when it went in the mouth then I won’t eat it. (I’ve even seen undigested greens in it)

    4. Colleen,
      I personally recovered from constipation by taking Magnesium. My dear old mother suggested it and it worked. I no longer take Milk of Magnesia, just magnesium citrate tablets, 2000 – 3000 mg daily.
      I initially tried high fiber, … disastrous.

    5. I found lots of fat helped me tremendously. Gives me energy and I don’t get constipation at all. In fact, that is my sign if I’m not eating enough fat. That and carb cravings. And weight gain… I think even if we know better, we are still programmed to think fat is bad. Hell, even after all this time I feel guilty when 1 throw a tablespoon or 2 of butter on my meat and veggies, but it makes me feel so healthy. I don’t know if this will help, but I really feel for your son…

    6. Have you ever tried cocnut water with pulp? It is sweet, it hydrates, and it has a decent amount of magnesium. I learned the hard way about its natural laxative affect.

    7. I have a child who holds. He doesn’t know any different because he got immediately constipated the day he started solid foods and stopped pooping because it hurt. He’s now five and he’s been off and on Miralax since 9 months old. He’s been solidly on Miralax for the last 9 months to un-stretch his colon and the Dr. says now to start taking him off it really slowly while adding in fiber so that he gets used to regular stools but I started that and he didn’t go for 3 days so I pulled out the fiber and upped his Miralax back to where it used to be. I’m sooooooooooo confused and feel like Colleen that we’ve been doing everything wrong. I know a lot of his problem is this unconscious physical habit of holding that started as a baby and he has apparently not really unlearned that but I hear all this confusing info about fiber and the Dr. wants him having a dose of psyllium in addition to the Miralax. I have no idea what to do. He drinks plenty, I can’t get him to use a stool at the toilet for a squat position as the Dr. suggests. I would also love any guidance anyone has.

      1. Our oldest was holding his poop in when potty training. He had eczema as a young, breast-fed baby. When we started solids, he got a lot of wheat-based products. Poop was inconsistent, and eczema was omnipresent, then, but it was going into a diaper. As we started potty training, he would hold it in for days until he couldn’t any longer. A few times his breath would smell like poop. It was terrible. His attitude also got worse and worse the longer he held it. After an hour long force to sit on the toilet session, he would poop and be so sweet again. The pediatrician recommended Miralax, which certainly works, but is a terrible long-term solution. However, we didn’t know what else to do at this time. He would get a small dose most mornings with his milk.

        Fast forward to me learning about primal/paleo and observing the changes for me. I realized my own bowel function suffers from wheat and dairy intake. I got my wife on board with the changes and we cut wheat and non-fermented dairy almost completely out of the kids’ diets. Since then, pooping has been much, much better. He goes nearly every day now, as do his younger siblings. Also, his eczema barely exists at all, anymore. The same is true of our youngest, who is a boy. The middle kid is a girl and she never has shown the same sensitivities as the boys, but she doesn’t drink milk or eat wheat either. In our studying eczema previously, I found research that kids with eczema have more attention problems and lower grades in school. Of course they do, their body is on fire on the inside! How uncomfortable and distracting.

        Your post was about poop however. We bought a book called “It Hurts When I Poop.” It has a story about a boy that doesn’t like to poop and it talks about how pooping is housekeeping for the body. It’s a pretty simple illustration and worked with our son when he was about 2, the lesson still sticks today, though we don’t have problems with this now (he is 4). We spent a lot of time sitting with him to help give him the moral support to get the poop out. All of that is helpful, but the poop will only improve with a good diet. Cut grains, dairy (we still eat a light amount of cheese), sugary drinks like apple juice and legumes. Do have them eat plenty of protein, vegetables, fats (macadamia nuts, coconuts flakes and avocados are a favorite at our house, even with the 1 year old) and have them drink water. We just keep water available and they do a great job staying hydrated on their own. One other thing is sometimes wiping was painful. We have found the Preparation H wipes with witch hazel work very well for cleaning and do not irritate the bottom. I usually use toilet paper for the first few wipes and the wet wipes for final clean up unless his bottom is irritated. He used to have a rash in that area until the dairy was cut completely. This is less of an issue now.

        The learned response part is tough and took us a good while to get past it. It’s important to support them in the effort and be patient. It’s going to take a while to unlearn their first reaction to it, but it definitely can be done. My wife made a sticker chart and pooping on the potty would result in a treat at some interval. All of the prompting has been unnecessary since we got his diet corrected to paleo norms. He just goes in and gets it done. Good luck!

        1. Thanks so much for the detailed reply. We have been wheat (gluten) free since before he was born. I haven’t had the heart to make everyone give up dairy though. Yogurt and cheese are some of the staples my kids love in their school lunches. We eat plenty of fat, protein and veggies. We are largely grain-free as well except I let my kids have rice crackers. I guess it’s those little things that might be exacerbating the problem. I just think I’ll have a mutiny on my hands if I take away dairy and rice crackers when every other kid is drinking juice boxes and eating goldfish or teddy grahams or whatever wheat-laden treat you can think of at school, there won’t be anything left to send for lunch….. I know it’s better for them but they don’t understand that, they only feel deprived.

        2. You are very welcome. That part of life is so much better for him and for us, I can only hope someone else can benefit from our experience.

          My kids’ diet is hardly sugar-free, but most of it comes from fruits and we try to skew a lot of that toward berries. My observation is that sugary stuff promotes constipation. I think cutting fruit juices was one of the more important moves along with milk and wheat. I think cutting the yogurt would help, partly because it is dairy and partly because they add so much sugar to it. There are some less sweetened yogurts out there, but they are hard to find. I don’t think the rice crackers are particularly harmful, but you never know until you try.

          I understand how it is to have your kid eat differently than others. We have emphasized to our son how those foods hurt him. The eczema made it easier. We talked to him about how his skin hurt when he had a rash and that it was because the food was making his body hurt from the inside. He used to rationalize “just a little bit wheat” quite well for a while so he could eat a cupcake or some crackers. Every time he did, he would get a light rash and/or the one on his bottom would show up. We emphasized that irritation and discomfort was caused by the food. Now, he is quite good at avoiding it. We also told him everyone’s body is different and that some people can tolerate some things that others cannot.

          Other adults have been at least as challenging to convince. We have been able to use the marked improvement in his skin as a good selling point for grandparents, etc., to honor our wishes regarding food. Maybe make some changes on your end and, if you see improvement, then you can sell the idea the same way. “Our child couldn’t poop regularly and had to be on somewhat toxic medication to help. If they avoid these foods, they can poop fine and avoid toxin exposure. It’s important.”

          Best of luck!

    8. Your post was quite a while back. I hope your son is feeling better. Miralax is not safe for anyone with digestive problems.

      I developed digestive issues and eventually, colon problems. It turned out my body cannot handle Chicory Root at all. Chicory Root is being added to almost all “prepared/processed” foods including Kashi protein bars, cookies, etc. It is, also, in Fiber One bars, most brands of ice cream, store bought bread, frozen vegetable lasagna, etc, etc, etc.

      Inulin added to food harms my body. I feel like this prebiotic thing is very much like “margarine is good for you and butter is bad”. That was untrue. I believe the prebiotics added to food will prove to be equivalent to the trans-fat disaster for Americans health.

      I went through years of increasing digestive problems. The doctors, originally, told me I would never have very serious problems because I ate so healthy. I ate lean meats, lots of veggies, good amount of fruit, etc. They, also, said to kick up my whole grains a bit just to be sure. Things gradually got worse.

      The more I added whole grains and protein bars to my diet, the sicker I got. It caused 2 1/2 years of colon infections. At that point, the doctors kept saying “you must be eating badly”. No. I did what they told me to do and got sicker and sicker.

      After 2 1/2 years of antibiotics and anti-nausea medication, ER visits, hospitalizations, unbearable pain, exhaustion, and misery I had colon surgery. They only removed 9″ of my sigmoid colon.

      I’m doing pretty well. My body will not tolerate chicory root at all. Chicory root is evil. 🙂 My body will not tolerate kefir at all. It can’t handle Stoney Field Farms Yogurt, but I can’t figure out why on this. I can eat Fage yogurt.

      I have, now, given up yogurt and probiotics. They cost a fortune and did not save me or restore my gut flora.

      It’s been 2 years since my surgery. Whole grains are not ok for me at all. Fermented products create a crisis, and the damage does not fully go away. I will not be trying any more “health foods”.

      Now, I am trying to restore my gut flora based on foods that were around in the 1950s and 1960s when I was growing up. Yes, that does make me older than some. 🙂
      I am 64 going on 26. It works for me. 🙂

      Post op, I ate grilled salmon and mashed potatoes with butter. Scrambled eggs for breakfast and salmon/ potatoes for lunch and dinner for about a week. It worked so well, I afraid to try anything else.

      Before the surgery, they had me go 12 consecutive days on clear liquids 4 times in 3 months. My body was not ok. I am ok now. I do have problems sometimes. I don’t go to the doctor because the do believe in Fructan Malabsorption. I’m not sure I have a malaborption issue. I can eat a ripe banana which has inulin. I can not tolerate inulin that is added to food.

      I’d appreciate if the jocks here could refrain from saying that if I were perfect like you, I would never have been ill. That approach is why I haven’t posted here before.

    9. Hi Colleen, our 5yo has this issue too. We’ve also done stool softeners and ‘ kid friendly’ laxatives to clear the blockage, with little success – if anything, I think it made him soil more. We think it happens because he gets ‘ too busy’ to go to the loo. Anyhow, we have had more success with hi fibre cereals (insoluble fibre) to flush It out and I make him flavoured milk with potato starch, plenty of unripe bananas, apples, oh and a very good 14 strain probiotic. Its hard as he is pretty fussy with veggies and meats but eats broccoli, carrot and I puree and hide other veg and legumes in sauces and stuff! Definitely seeing progress. I hope we can establish better toilet habits this way and slowly wean him off the hi fibre cereals! He also has try times on the toilet at morning and evening and he takes the iPad in to make it less confronting. Best of luck, it is not a quick fix!

    10. My daughter used to suffer with stomach pain and after increased fiber, she would still have pain even though she would have enormous poops. They would be soft, so I thought there was no way she could be constipated. After x-rays confirmed that she had so much bulk in her intestines a physician’s assistant told me not to give her all that fiber and to start feeding her more berries, apricots, apples… basically things with a lot of pectin in it. He said that we don’t need all that fiber and kids are more sensitive to it. After increasing pectin foods and decreasing fiber her stomach pains went away and she was fine. No more massive poops either.

  22. Thank you for always linking REAL sturdies to your articles. It really is appreciated

  23. I think “double decker” should have been “upper decker” – much more appropriate for your sworn enemy!

  24. I’ve gone for long stretches eating only meat and my bowel movements have been perfect.
    I’d even go so far as to say exquisite and beautiful.

    The first few days without all the usual fiber can be a bit tricky though.
    Takes discipline to get through that.

  25. I’m concerned we’re missing a correlation here. The post states that gut flora composition from fermentable fibre is critical to “good” health. But is it possible that you only need this particular flora if you consume fibrous foods?
    In other words, the claimed “good” flora might only be good if you’re a fibre consumer, but if you’re not, is it possible that the particular flora is unnecessary?

    1. I agree with this viewpoint – it is all to easy to come to erroneous conclusions when you are looking at the evidence through the ‘lens’ of a long-standing, preexisting set of circumstances.

      I also find that my bowel movements and stools are much ‘healthier’ without dietary fibre (usually, I consume hardly any – either via plants or supplements). However, when I deviate from my habitual food choices and do eat something with fibre (nuts, for example), I pay for it with gut pains, bloating and hard, difficult to pass stools!

  26. I just leaded up with some insoluble fiber…and since I’m my own worst enemy I’m dropping an upper-decker on myself!

    Good God! That had me howling!

  27. Thanks for this Mark!

    Did you know you were seeing the future back a couple years ago when you wrote about ‘parboiled rice’?

    You said: “Parboiled rice is interesting. Parboiling involves partially boiling the intact rice seed – husk, bran, and all. This, in theory, is supposed to incorporate some of the bran’s nutrients into the interior. The parboiled rice is then dried and milled, producing a white rice with greater nutrient content than regular white rice. How does it pan out? …It kinda works. There’s very little mineral change from white rice (perhaps even a reduction), but some of the vitamins seem to increase by parboiling. Interesting.” (Read more:

    Well, it turns out that the parboiling process actually creates resistant starch in the rice by heating it under pressure and then cooling it. Wikipedia explains it like this:

    “The starches in parboiled rice become gelatinized, then retrograded after cooling. Through gelatinization, alpha-amylose molecules leach out of the starch granule network and diffuse into the surrounding aqueous medium outside the granules[4] which, when fully hydrated are at maximum viscosity.[5] The parboiled rice kernels should be translucent when wholly gelatinized. Cooling brings retrogradation whereby amylase molecules re-associate with each other and form a tightly packed structure. This increases the formation of type 3-resistant starch which can act as a prebiotic and benefit gut health in humans.”

    So, for your up-and-coming rice-eaters, my money is on parboiled, AKA converted rice. Lowest GI of all rices, more nutrition, and a hefty dose of prebiotics.

  28. All I know is that I suffered the worst constipation of my life eating my parents way… high fibre Pritikin type diet all through my teens. We avoided fats and ate lite everything and I ate lots of carbs and starchy veggies. My teenage years I was eating the healthiest food of anyone I knew… went to McDonalds twice before I was 16… parents did aerobics 7 nights a week… etc etc etc. My mother who had bowel cancer in her late 40s should have been the picture of bowel health… talk about eat some serious fibre….

    As soon as I switched to low carb, and upped my good fats, my toileting habits significantly changed. Admittedly I suffered terrible constipation and gut pain for the first few weeks (and bought some fibre drink thing to combat it) but after those first weeks I settled into a new rhythm bathroom wise.

    I go less often and the amount is less. I never strain, worry or have to read an entire chapter of a book to “go”.


    There are many great things about primal eating… this is up there with the weight loss (35kg) one of the best things about eating this way. Thanks Mark… 🙂

  29. Another great article Mark. Love the fact that you are a healthy person yourself so I know I can trust what you write.

  30. Wow! I thought people were passionate about fiber. They are way more passionate about their poo.

  31. This came from

    A commenter said:

    “I think that Mark Sisson and Paul Jaminet will both say that eating as they describe will provide one with all the pro- and prebiotics one needs to thrive.

    I think differently. I think their plans are a good start, and adequate for long-term good health, but more indepth looks at the role of prebiotics on proper gut function, and evidence from our ancestors petrified poop, shows that our gut microbes evolved on a diet high in fermentable fiber (prebiotics) and that about 20g per day is needed to optimize the growth of beneficial microbes and keep pathogenic types at bay.

    A Primal Blueprint Big Ass Salad, or a Perfect Health Diet day with one pound of veggies, depending on food choices, could net someone about 5g max in prebiotics.

    Take a look at this paper:

    It shows the average intakes of inulin and oligofructose (the main non-RS prebiotics) for SAD eaters in the mid-90?s. The average intake was about 5g–with 70% of that coming from wheat products!

    The advice of the 80?s and 90?s to ‘eat more fiber’ really did nothing to increase our intake of prebiotic fermentable fiber, but led to the inclusion of all types of filler fibers in bakery treats and snacks–to make them ‘healthy’ snacks.

    So, when you adopt a paleo style diet, whether PHD or Primal Blueprint, you take away grains and replace them with more veggies, but at a deficit of overall prebiotic fibers. Then we demonized legumes, potatoes, rice, and starchy fruits like bananas and plantains which takes away any hope of resistant starch for prebiotics.

    What I am proposing, is that a healthier way of eating can be had by continuing with the Big Ass Salads, but also add in known RS sources: beans, bananas, plantains, potatoes, rice, as desired, and a bit of raw starch if you are slacking in the real food compartment or just want to up the ante a bit.”

  32. Amazing to read this just when my husband had started complaining that his ‘toilet habits’ weren’t like they used to be and he thought he was constipated! Now I realise that what we are both experiencing is normal after a few weeks of eating in a primal style.

    Loving this life style change 🙂

  33. Really interesting!

    When I first was trying to change my gut health (GAPS diet), I couldn’t get enough onions. I would make a bunch of veggies and onions and I’d end up picking out all the onions because that was what tasted good to me. I wonder if my body knew I needed them?

  34. The replies to this post tell me that most people do not understand the concept of prebiotic fiber.

    Using a nutrition label to get adequate fiber for prebiotic purposes will do the exact opposite of what you are trying to do…it will get you loads of non-fermentable fiber and fiber that is fermentable by the wrong species of gut microbes.

    As Mark said in the blog above:

    “You should introduce foods rich in soluble, fermentable fiber gradually and even cautiously. Allow time for your gut flora to adjust to the new food source. Expect flatulence….But you should definitely introduce them.”

    Studies show that an intake of 10-30g/day of prebiotics is optimum, and it takes 3 weeks to even out the microbial populations. Plan on a 3 week phase-in period, start at lower amounts. Too much too soon will result in major gas and bloating.

    And Mark said:

    “Eventually, you’ll be able to fish a sample out of the toilet, snap a shot of it with your iPhone camera, and have your entire gut microbiome analyzed on the spot, complete with dietary fiber recommendations for optimal butyrate production and minimal flatulence, but that’s a long while off.”

    Actually, it’s not that far off–the American Gut Project will mail you a swab kit and analyze your gut flora and compare you to the rest of the world based on eating habits, $99.

    and Mark said:

    “Scientists are still figuring out which gut flora are best, which species are good and which are bad, what kind of fiber source they like, and how often and how much we should feed them. In other words, we’ve reached the stage of knowing enough to know that we know very little. In the meantime, we know “gut flora are important.” We have vague ideas of which populations are “good” based on correlative studies that link certain species with diseases.”

    There are thousands of species in our guts–some we will never understand. But we do know, without a doubt, that healthy people have guts dominated by a strain known as ‘Bifidobacteria’ and that unhealthy guts are associated with ‘Enterobacteria’. These microbial populations are easily reversed with diet. A diet low in prebiotics and high in SAD foods causes a gut filled with Enterobacteria, leads to leaky gut, auto-immune conditions, lactose intolerance, poor glucose regulation (insulin resistance), hypercholesterolemia, and poor absorption of minerals. A diet high in whole foods with minimal sugar and loads of plant prebiotics ensures a gut dominated by Bifidobacteria and better glucose regulation, lipid oxidation, robust immune response and healthier colons.

    And Mark said:

    “We know we need gut flora because of their endless interactions with the host, and that they need food. We know that the plants (and breast milk) we eat provide that food.”

    Here’s my thoughts on how to easily take charge of this issue:
    1. Eat your daily BAS
    2. Eat fermented foods (yogurt, kefir, sauerkraut, etc..) often.
    3. Avoid sugar, flour, and vegetable oils
    4. Specifically target foods high in resistant starch…greenish bananas, raw/dried green plantains, cooked and cooled potatoes and rice, and properly prepared legumes. RS is easier to get in larger amounts than inulin and other prebiotics!
    5. They sell all kinds of prebiotic supplements. Most contain 1-3g of inulin, pectin, or gums. Some are resistant starches made of special corn or barley. If you want to supplement your prebiotic intake, I like unmodified potato starch (not flour), tapioca starch (AKA tapioca flour), and plantain flour. These need to be added to a smoothie or a cold drink–can’t be heated. 1TBS contains about 8g of prebiotics, and will not cause blood glucose to spike in the least. These real-food items are cheap and last a long time, prepackaged supplements contain fillers (often wheat) and are expensive.

  35. I think guy flora is the basis for a procedure that takes healthy weight people’s stools and puts it in obese people. I think the theory is the healthy person’s flora will help reset the balance of good vs bad in the over weight person’s gut.

  36. I never had constipation issues before I went Primal over a year ago, but after about a month or so my bowel movements became very difficult. My poop is hard and painful to pass, and when I wipe there is only a bit of blood – It’s almost like I don’t really need to wipe at all!

    Not sure what to do about this; I’ve just been tolerating it ever since it started.

  37. Okay, I guess this is the best post for me to ask my very basic question:
    Do I have to eat vegetables?
    I really don’t like them and have only ate them because I was trying to be a good boy. The ones I do eat since going Paleo are sweet potatoes, onions and garlic (just because they season my meat nicely).

    I eat fruits rarely, maybe 2 or 3 times a week.

    In the past I always ate salads, broccoli, blah, blah, blah,… but I rather not. I know that they’re are rich in minerals and stuff, but am I okay without them?

    I am taking a good Probiotic supplement, Vitamins D3 and C as well as Omega 3’s.

    It’s kind of obvious the answer I’m looking for, but I’m willing to what’s best regardless.

    Thanks to all 🙂

  38. Help! Impacted bowel in 85 year old…Been reading all these comments avidly waiting for some comments about the value of chia seeds but no mention! How come? I was hoping that I might find some insight for helping with my elderly Mum’s issue of impacted bowel for which she was hospitalised for afew weeks ago. She has some narrowing of the colon. She has been prescribed Movicol sachets which look just like chia gel when made up. But she’s not taking them regularly as had afew issues with overflow. The consultant (we are in the UK here) had never heard of chia and dismissed them as non evidence based mumbo jumbo

  39. I have always known that I need to either eat a salad or a big plate of fresh fruits for lunch every day that’s the only way I stay regular. I have Hashimoto’s Hypothyroidism and one of the side effects is constipation but if I eat my fruits or salad I don’t have that problem.

  40. Super disappointing in Mark for missing the mark and addressing a bigger picture. Everything about fiber and what it should be doing for your body and what it fails to do… Nothing in the article about Fiber being ESSENTIAL for DETOXification. NOWHERE in this article is the word Detox even used! C’mon Mark, dig a little deeper and look at the next level or what fiber is doing for us not just surface idiocy about how big your stools are. Your system needs to flush and cleanse toxins through which fiber, in addition to water, does. I was inadvertently poisoned by pesticides and had to heal myself and did extensive research into detoxing and thank God, came back from that horrendous experience.. Fiber is key to your body ridding itself of waste buildup in the intestines. Additionally, I was having major issues from lack of fiber in my rectum area, dealing with fissures… After multiple issues and two doctors visits and having surgery there, not a single MD said fiber would help prevent these issues…After increasing my fiber, not a single issue there in an area that MD’s said would be chronic my whole life. We must be our own doctors and do our own research to heal ourselves. TRUST ME, Get your proper fiber intake!

    1. Katie C. Exactly. Try checking out fiber microbiome on google . Fiber has an incredibly important symbiotic relationship with our brain and every other organ we have. Google them. Also, there is research going right now linking high fat western style diet (meat) to colon cancer because of the deoxycholic acid (DOC) involved in changing the DNA lining our gut walls. These mutations change the activity of cancer-related genes. Google “Bile Acids link high fat diet to colon cancer”. Godo luck

    2. Hope you see this. How much fiber you were taking before and how much you increased?

    3. Katie,

      Hope you see this. How much fiber you were taking before and how much you increased?

    4. Katie,

      I Hope you see this. How much fiber you were taking before and how much you increased?

  41. Hi, i’m doing a low carb, healthy fat diet, but I have constipation, very hard stools and I don’t what to take for it, I’m so confused one expert says this the other one says something else, what do you recommend?.

  42. So… What about FODMAPs? You mentioned garlic and onions are a great way to feed your gut bacteria, but what about FODMAP-sensitive individuals (like me)? I have been observing myself for quite a while, been on an extremely low FODMAP diet and every time I try to reintroduce for example garlic or onions – I can’t. Even in reasonable quantities, I get extreme bloating and gas that prevents me from leaving the house and having any social life… Not to mention the discomfort and the constipation that most FODMAPS cause for me. The literature on FODMAP-sensitive guts is very limited, so it would be great if you could elaborate on it. I mean the correlation of the kind of fiber you recommend and the FODMAP sensitivity. In my case, it seems that it’s only harming me and my gut…

  43. Hi Mark,
    I’m now totally confused! I accept Kellogg was a loony but what about all the rest of folk (including you, Mark) who support fiber?
    Since going keto (successfully to nutritional daily and optimal regularly) I’ve become constipated and stopped losing weight. I’m just about to add Psyllium to my keto pancakes – am I completely wrong? And where do I find the evidence?