Doctor's Note

This mechanism is similar to how "normal" levels of fiber consumption (huge by modern standards) relieve the body of excess estrogen, which may explain reduced breast cancer risk in those eating plant-based diets. Fiber also helps improve intestinal transit time (stool size matters!) and protects against diverticulosis. An explanation of the nitric acid effect can be found in The Power of NO and the magnesium data is in How Do Nuts Prevent Sudden Cardiac Death?  and Mineral of the Year: Magnesium, and Friday's video-of-the-day Nuts and Bolts of Cholesterol Lowering covered the cholesterol angle. The next two follow-up videos will use the same trash-picker analogy to explain the actions of phytosterols. If you haven't yet, you can subscribe to my videos for free byclicking here.

For more context, check out my associated blog posts: Stool Size and Breast Cancer Risk and Treating Parkinson's Disease with Diet

  • Michael Greger M.D.

    This mechanism is similar to how “normal” levels of fiber consumption (huge by modern standards) relieve the body of excess estrogen, which may explain reduced breast cancer risk in those eating plant-based diets. Fiber also helps improve intestinal transit time (stool size matters!) and protects against diverticulosis. An explanation of the nitric acid effect can be found in The Power of NO and the magnesium data is in How Do Nuts Prevent Sudden Cardiac Death?  and Mineral of the Year: Magnesium, and Friday’s video-of-the-day Nuts and Bolts of Cholesterol Lowering covered the cholesterol angle. The next two follow-up videos will use the same trash-picker analogy to explain the actions of phytosterols. If you haven’t yet, you can subscribe to my videos for free by clicking here.

    • SJ M.D.

      Well – now we also have an explanation for “Big poop small hospital, small poop big hospital”…..

      • Veganrunner

        Dr. gregers blog, Bowel Movement and The Scoop on Poop is a timely review on fiber.

  • BPCveg

    To use the river analogy, if fibre speeds up the flow, is it possible that too much fibre in the diet could lead to reduced absorption of vital nutrients?

    If so, what is the optimal amount of fibre to consume?

    • Veganrunner

      BPCveg, such an interesting question. After I started on my morning “blended salad” i must have really increased my fiber. I had to increase my thyroid medication. When I went on the sythroid website it said an increase in fiber could cause decreased absorption. Crazy right?

      • Mands121

        Veganrunner, crazy right? Not exactly.
        Your increased fibre consumption seemed to cause decreased absorption of your medication. This backs up the point of the video.

        • Veganrunner

          Exactly!

      • 4ever learning

        No, Veganrunner, I don’t think it’s crazy as the preferred origin of your thyroid hormone would be internal and not through the mouth with eventual passage through the stomach and intestines.

        As for optimal amount of fiber, BPCveg, I don’t think most people are even close to having enough fiber, never mind worrying about too much. My thought is that the body “knows” what it needs and will become more or less efficient at absorbing nutrients if one supplies the right foods. 

        • BPCveg

          Probably true about most people not getting enough fiber, but many of those following Dr. Greger are eating lots of fruits and vegetables in an effort to optimize our diets.

          If you listen to Dr. Greger’s argument in the video between 2:05 and 2:11, he is arguing that the waste excretion is rate limited and therefore increasing bulk flow through higher fiber intake will help this process along.  I am asking the reciprocal question. Since we know the rate of nutrient absorption is also rate limited, wouldn’t too much bulk flow (caused by overconsumption of fiber) reduce the net amount of absorption?

          • 4ever learning

            BPCveg, I agree there is a ballpark figure for optimum fiber and I understand your argument. However, rate limiting via transit time is a variable, but probably not the only variable. If transit time is shortened, I might speculate that the body will recognize this and change the efficiency of absorption of the nutrients. For example, doesn’t the body modify the amount of non-heme iron absorbed in a vegan diet based on need? 

          • BPCveg

            4ever learning: I think you make a good point about absorption rate being modifiable to a large extent, which is probably a protective mechanism of the body to prevent overload of certain nutrients.

            I suspect, however, that there is an upper limit to absorption of most nutrients. In the case, of iron, I speculate that a vegan who is trying to raise iron levels by consuming non-heme sources and who is consuming an extreme quantity of fiber may struggle to absorb enough non-heme iron since the iron absorption rate may saturate, while the clearance rate, due to extreme fiber, may be too high.

          • 4ever learning

            You made your point! :)

        • Veganrunner

          Seeing that all I eat is vegetables, fruit, legumes, grains( no gluten) nuts and seeds there is absolutely no way I could further increase my fiber. And Nothing processed.

      • WholeFoodChomper

        Veganrunner, did it say that it was overall fiber intake that might affect thyroid hormone absorption, or was it dependent on when you last ate your high fiber meal? For example, to not alter the absorption of my thyroid hormone, I take it on an empty stomach and do not eat anything afterwards for at least 1 hour. I also take my vitamin B12, omega 3s, and vitamin D 5 or more hours later to not affect the thyroid hormone absorption rate as well.

        • Veganrunner

          Overall fiber. I do the same. Pill in the morning and I eat and drink nothing for at least 2 hours. I hadn’t changed anything else in my diet.

          • WholeFoodChomper

            Interesting,indeed. Sounds like I’ll need to keep a closer look at my thyroid hormone levels as well.

    • Mands121

      BPCveg, the fact that the comparison of the Paleolithic diet Vs Modern diet is what Dr. Greger shows on the video, I therefore assume that the 104g of fibre in the Paleolithic diet is what we strive to achieve.

      • BPCveg

        Correct me if I am wrong, but isn’t the common rationalization for paleolithic diets that humans have been following these diets for vast periods of time and therefore should have evolved (i.e. physically adapted) to eating that way?

        My understanding of the established darwinian evolution by natural selection is that  for an adaptation to occur, the fitness of
        individuals (i.e. the ability to pass on their genes to offspring) must be changed. It doesn’t seem to necessarily be true that following a specific dietary pattern for any length of time will result in changes in our genetics. 

        For example, suppose we humans continue to use computers for another million years. Will that mean that humans will have evolved to use computers? These kinds of vague evolutionary arguments never convince me.

        I am interested in learning about diet by understanding physiological mechanisms that can be rigorously tested on humans that are alive today!

        • Mands121

          I agree we have evolved to eat the paleolithic diet.
          I did see once in a documentary about “survival of the fattest”. Where during the last ice age the fattest of the population tended to survive because they lived longer off of their fat supplies. http://www.youtube.com/watch?v=Nkh9fz9WkwA

          I can only imagine that if we use computers even for a short amount of time, our brains change/adapt to this. It is well known that London black cab drivers brains grow as they learn,  http://news.bbc.co.uk/1/hi/677048.stm

          The fact we are all different, (body types, metabolisms, gut flora, good/bad hormone production, etc) says to me to follow proper research and advice, like nutritionfacts.org.

          Your belief system about evolution and the past and how you react to certain food should guide you the rest of the way.

          • http://www.facebook.com/pedro.flores.9461 Pedro Flores

            i highly doubt that humans can actually evolve to use computers since we live in an environment where our survival doesn’t even remotely depend on our ability to use computers.

    • BPCveg

      I am now thinking that high fiber intake could even reduce the number of calories that we absorb from food. This could partly explain why those following diet tend to gain less weight than omnivores, even after controlling for calorie intake and energy output.

    • http://www.facebook.com/profile.php?id=526970694 Vicki Reesor

       BPCveg, I suspect that the amount of fibre in a given diet is self-limiting.  Anybody eating “too much fibre” would be calorie deficient, and would self-adjust for this.  It’s my understanding that an appropriate balance of calories and phytonutrients in the diet arising from a variety of plant-based whole foods will naturally contain “just the right amount” of fibre, and will result in appropriate nutrient absorption.  But this is mainly just my “gut” feeling…

  • john

    i almost died from eating too much fiber. my stool was so big that i couldn’t even flush my stool in the toilet. thanks to gut sense by after reading the fiber menace book. i recovered by my haemorrhoids and constipation. 

    • WholeFoodChomper

      My goodness, how much fiber were you eating?  Was it all plant-based, or where you also taking supplements? Where you drinking enough water?

    • anonymous

      all the advice I’ve read about fiber is to add it slowly to allow the body to adjust.

  • Sandra Derr

    I look forward to your lessons in my e-mail daily. Thanks for being so talented at explaining things I probably would not understand. I started a vegan lifestyle over a year ago and love feeling validated for my choices to eat lots more fiber.

  • BPCveg

    Noted vegan physician, Dr. Caldwell B. Esselstyn, Jr, claims on his website (Q&A section) that we should avoid smoothies because “The fiber is so finely pureed that its helpful properties are destroyed”.  Is there any scientific evidence to support this claim?

    • veganrunner

      That goes against Dr. Gregers videos, as well as Dr. Fuhrman who says absorption of important nutrients is increased by 50%. Dr Esselstyn comment doesn’t even make physiological sense. Regardless, fiber still goes through the same intestinal track and is not absorbed. 

      One reason people drink smoothies is because you can get a lot of nutrients in a very concentrated form. As far as my running goes–oatmeal doesn’t sit well and I can drink a smoothy and run right away. I appreciate that you all love to cite research but personally I don’t have the time, so you will need to check it out for yourself. (but then again you didn’t check Dr. Esselstyn’s comment out so maybe I am in the clear! ;-) 

    • veganrunner

      Hi again BPVeg,

      A book I have found helpful on so many of these topics is Integrative Gastroenterology written by Gerard E. Mullen, MD (he is a gastroenterologist.) He has also written The Inside Track which is a easy read for the less medically inclined. He deals mainly with healing the gut but the physiology of how the gut works is explained well. 

      • BPCveg

        Veganrunner: Thanks for this book recommendation. Seems quite holistic, based on the table of contents.

        By the way, the reason I didn’t cite Dr Esselstyn’s website is that it is a commericial site and Dr. Greger prefers to limit posts that contain such links; a challenging goal, but I respect him for it.  

        • veganrunner

          Oh but I bit. I couldn’t find anything on Medline. That is what I love about this website–Dr. Greger and crew does all the work so “we don’t have to!”

          Another interesting aspect is the role fiber plays with intestinal bacteria. We traditionally think of its role in moving things along but it also “feeds” the good bacteria in our gut.

          Yes Integrative Medicine is holistic but I find that refreshing. Dr. Greger is an integrative physician in that he recommends nutrition for what ails you. In addition herbs are discussed here frequently. The majority of physicians would never discuss the role nutrition plays in our health. 

          I am a physical therapist with a practice that specializes in orthopedics. My practice is based on the best current research. We know that stress plays a huge role in our health. Again integrative medicine. So ideally MD’s would discuss all aspects of ones health but we barely get any more than a perscription for a medication. (except for Dr. Hemo and Dr. SJ. They are the best!)   

    • j oraknabo

      I’m not sure what the exact study is he’s citing here, but starting at 6:48 on this video http://www.youtube.com/watch?v=X6ogG1wEcXo, Jeff Novick makes an interesting point about how the satiety of an apple is changed by blending it.

      • BPCveg

        j oraknabo: please see my response to you below.

  • BPCveg

    Excellent points.

  • BPCveg

    (comment removed)

    • WholeFoodChomper

      You may want to write an email to the Disqus (http://disqus.com/) to see why your links are not posting and what you can do about it. Sometimes my links do not post or get cut off as well.  I think it has to do with the comment platform (which is being provided by Disqus) and not the NutritionFacts web-site.  Specifically, you can go here (http://help.disqus.com/ ) for technical help with posting comments using Disqus.

      • BPCveg

        Thanks again!

  • BPCveg

    Thank you very much for providing this video. I agree that Jeff Novick tries very hard to convince us that simply blending apples can lead to different satiety than eating the whole apple. However, for reasons I describe believe he falls short. 

    I found the study he cites “The effect of fruit in different forms on energy intake and satiety at a
    meal”, 2009,
    Appetite 52: 416–422.
    Full text available at:
    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2664987/pdf/nihms97426.pdf

    In the youtube video from 11:03
    to 11:12, Novick describes the manner of applesauce creation as follows:

    “so
    they bought one of those fancy blenders, you know which ones, and they put the
    apple in it and they turned it on and it wizzed” 

    However, the paper that he cites gives a very different description of the applesauce preparation on page 3, paragraph 3:

    “In order to make the applesauce, apples were
    peeled and baked in a covered dish for 45 min at 177 °C. The apples were
    weighed before and after baking to measure the amount of water that was lost
    during baking, and water was then added to the apples to account for any water
    loss that occurred. The apples were then pureed to produce applesauce.”

    Sorry, but this isn’t the same as just blending apples!

    • j oraknabo

      Thanks for pointing that out. Considering that just moments before that, he mentions the advantage of the water in soup, I’m surprised he wasn’t aware that water had been removed from the apples.

      While I’ve clearly understood the problem with removing the fiber in the juicing process, I’ve always been a little skeptical about claims about blending. If blending destroys the helpful properties of food, then are people who thoroughly chew their food going to be severely malnourished.

  • BPCveg

    Thank you very much for providing this video. I agree that Jeff Novick tries very hard to convince us that simply blending apples can lead to different satiety than eating the whole apple. However, for reasons I describe believe he falls short.

    I found the study he cites “The effect of fruit in different forms on energy intake and satiety at a meal”, 2009, Appetite 52: 416–422.
    Full text available at:
    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2664987/pdf/nihms97426.pdf

    In the youtube video from 11:03 to 11:12, Novick describes the manner of applesauce creation as follows:

    “so they bought one of those fancy blenders, you know which ones, and they put the apple in it and they turned it on and it wizzed”

    However, the paper that he cites gives a very different description of the applesauce preparation on page 3, paragraph 3:

    “In order to make the applesauce, apples were peeled and baked in a covered dish for 45 min at 177 °C. The apples were weighed before and after baking to measure the amount of water that was lost during baking, and water was then added to the apples to account for any water loss that occurred. The apples were then pureed to produce applesauce.”

    Sorry, but this isn’t the same as just blending apples!

    • WholeFoodChomper

      BPCveg, that is an issue for Disqus and not Nutrition Facts.  I’ve had the same annoying problem.  I emailed Disqus about it and they said that they are looking into it. You may want to let them know that you are having the same issue to get the ball rolling quicker.

      What has worked for me in the past is to delete the text and replace it with sort of symbol (since Disqus will not allow you to leave a blank comment).  Then go to your Disqus profile and delete the comment.  All it will do is alter the comment to Guest (which will unlink it from your profile and prevent you from making any changes to it in the future… so be careful if you choose this method.)

      • BPCveg

        WholeFoodChomper: Thanks a lot for the great tip!

  • WholeFoodChomper

    Great video and information, as always. It’d be great if this video had the tag “Paleolithic” attached to it. It’d be great to be able to search videos for this term in the search function and under the “Video Topics.” ;-)

  • JamesKB

    Probably a pointless question, as people who eat a high fruit and veg diet likely have a lot more minerals and vitamins floating around their blood, but does this mean nutrient absorption is impaired on a high fibre diet, because of the speed up?

  • http://www.facebook.com/scott.higgins.9210 Scott Higgins

    I’m a huge fan of your work and have since changed my diet to a vegan based diet. My question if for my mother. She has been eating a vegan based diet for three years now with very low amounts of oil, yet her cholesterol is still in the mid 200′s. She takes medication for a “low thyroid”. Do you have any recommendations on how to lower her cholesterol through diet???

    Thank you for all your work!!!

  • Sallie

    What about the cholesterol-lowering effects of soluble fiber? If insoluble fiber speeds up motility and soluble fiber slows motility to increase satiety, how does soluble fiber mediate its cholesterol-lowering effects?

  • dogulas

    Where did paleolithic diets get all that calcium? Was it really likely from massive amounts of greens?