For decades, fiber has been touted as an essential component of a healthy diet. The supposed benefits of a high-fiber diet have been drilled into us through recommendations by our doctors, government, and the food industry alike, yet many of these health claims have not been proven by research.
In fact, many studies have demonstrated that excess intake of fiber may actually be harmful, particularly for gut health.
The majority of the research supporting the benefits of dietary fiber come from epidemiological studies that link the consumption of fiber-rich fruits and vegetables with a lowered risk of certain diseases such as obesity, heart disease and cancer, particularly colon cancer. (1) Yet when tested in the lab, controlled intervention trials that simply add fiber supplements to an otherwise consistent diet have not shown these protective effects. (2) (3) (4)
The Institute of Medicine recommends a daily fiber intake of 38 grams for men and 25 grams for women (5), which may come from dietary fibers, both soluble or insoluble, or the addition of “functional fibers” to the diet. The IOM defines functional fibers as non-digestible carbohydrates that have been isolated or extracted from a natural plant or animal source, or they may be manufactured or synthesized. Examples of functional fibers are psyllium husks, chitin from crustacean shells, fructooligosaccharides, polydextrose, and resistant dextrins. (6)
These functional fibers are often added to processed foods as a way to bulk up the fiber content for consumers looking to meet the IOM intake guidelines. A recent report by NPR commented that despite the lack of significant evidence linking fiber intake to health outcomes such as reduced heart disease or cancer, many consumers are buying foods that are fortified with synthetic fiber additives under the guise of health promotion. (7) Three grams of added fiber is enough to allow these food products to claim to be a good source of fiber, and the food industry has used these fiber guidelines as a way to increase their sales of grain-based products in particular. (8)
Tan and Seow-Choen, in their 2007 editorial on fiber and colorectal disease, call insoluble fiber “the ultimate junk food”, as “it is neither digestible nor absorbable and therefore devoid of nutrition.” (9) Excess insoluble fiber can bind to minerals such as zinc, magnesium, calcium, and iron, preventing the absorption of these vital nutrients. (10) Large excesses of certain soluble fibers like pectin and guar may also inhibit pancreatic enzyme activity and protein digestion in the gut, leading to an anti-nutritive effect. (11)
The addition of insoluble and soluble fibers to processed foods may actually cause these foods to be even less nutritious than if they were not enriched with any fiber at all.
A high-fiber diet has also been described as a preventative strategy for the development of diverticulosis, a disease that is markedly more common in Western countries. However, when researchers tested the theory that a high-fiber diet prevented diverticulosis, they not only found that a high intake of fiber did not reduce the prevalence of diverticulosis, but that a high-fiber diet and greater number of bowel movements were independently associated with a higher prevalence of diverticula. (12) Interestingly, this study found no association between the presence of diverticulosis and red meat intake, fat intake, or physical activity, which are other factors commonly attributed to diverticulosis.
The researchers hypothesized that one possible effect of a high-fiber diet in the development of diverticulosis could be the quantitative and qualitative changes in gut bacteria due to the excessive fiber intake. Both insoluble and soluble fibers are shown to alter gut bacteria in as little as two weeks. (13) It is possible that the high levels of excess fiber and overgrowth of intestinal bacteria may have contributed to the development of diverticular pouches in the colon.
This hypothesis brings up another side to the fiber debate: the effect of dietary fiber on beneficial gut bacteria, as well as the bacterial fermentation of undigested soluble fiber into short-chain fatty acids such as butyrate. When we eat the soluble fibers found in whole plant foods, the bacteria in our gut ferment these fibers into short-chain fatty acids like butyrate, proprionate, and acetate, and greater amounts of fiber consumed will lead to greater short-chain fatty acid production. (14) In this case, naturally occurring soluble fibers are very important for feeding the friendly bacteria that live in our guts.
One of the risks of long term very low-carbohydrate (VLC) diets, in my view, is the potentially harmful effect they can have on beneficial gut flora. VLC diets starve both bad and good gut bacteria, which means these diets can have therapeutic effects on gut infections in the short term, but may actually contribute to insufficiency of beneficial strains of gut bacteria over the long term. Providing adequate levels of carbohydrate and soluble fiber to feed friendly bacteria is important for optimizing digestive health and maintaining the integrity of the gut lining through the production of short-chain fatty acids.
Stephan Guyenet has written an excellent blog post describing the benefits of butyrate and other short-chain fatty acids on the maintenance of healthy gut integrity. (15) Butyrate has anti-inflammatory effects, increases insulin sensitivity, and may delay the development of neurodegenerative diseases. It may also be helpful in the treatment of diseases of the colon such as Crohn’s, IBS or ulcerative colitis. (16)
Stephan believes that butyrate may play a significant role in healthy metabolic function, stress resistance, and the immune response. He also asserts that the epidemiologically observed benefits of a diet high in naturally occurring fiber are likely due to the higher butyrate production from these diets. In this case, a higher fiber diet could be protective and beneficial for health, particularly if the fiber is soluble.
So what does this mean for our own consumption of fiber?
Ideally, dietary fiber should be coming from whole food plant sources. Many foods in the Paleo diet are great sources of both soluble and insoluble fiber, such as yams and sweet potatoes, green leafy vegetables, carrots and other root vegetables, fruits with an edible peel (like apples and pears), berries, seeds, and nuts. Interestingly, butyrate itself is also found in high-fat dairy products such as butter and cheese, and can also be provided by the bacteria found in fermented foods. (17)
Although I recommend that most people get fiber from whole foods, there are some people that may benefit from soluble fiber supplementation – including those that aren’t able to eat fruit or starch due to blood sugar issues or weight regulation, and those with severely compromised gut flora or gut dysbiosis. In these cases I’ve found soluble fiber and/or prebiotic supplements to be helpful.
For healthy people, including a variety of fibrous whole plant foods, fermented foods, and high-fat dairy as tolerated should eliminate the need to supplement with extra fiber, especially those insoluble fibers that are from sources high in anti-nutrients. A Paleo diet with some level of attention paid to the quality and quantity of vegetables, fruits, and starchy tubers can provide adequate levels of soluble fiber to feed the friendly bacteria in the gut that convert these fibers into beneficial short-chain fats like butyrate.
Recommended supplements if needed:
Prebiotic: Klaire Labs Biotagen
Soluble fiber: Organic Acacia Fiber
Caution: it’s crucial to start with a very low dose of prebiotic or soluble fiber and build up slowly over time. This will minimize any potential adverse reaction that can occur with significant changes (even positive changes) to the gut microbiome. For Biotagen, start with 1/4 of 1/8 of a tsp (1/32 tsp.) and increase by 1/32 of a tsp every 4-5 days. For Organic Acacia Fiber, start with 1/4 of a tsp. once per day and build slowly from there.
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{ 33 comments… read them below or add one }
Thanks for a clear and well-researched article! Very interesting to read about the “fiber-added” processed foods – I haven’t noticed many of these on this side of the Atlantic, but I’ll be watching closely from now on.
David
What about white potatoes? I don’t handle yams or sweet potatoes well, but seem fine with white. Am I getting soluble fiber from them?
Thanks!
Great post. As someone who had a colon resection for diverticulitis (at 40), this is a particular interest of mine.
The fiber hypothesis comes from Dr. Dennis Burkitt, who was practicing in Africa as the diseases of civilization began to emerge there. In “Diseases of Civilization, their Emergence and Prevention”, he details the spread of diverticulitis, along with other diseases of the gut, as the locals eat less fiberous foods and more wheat flour and sugar. He presumes that the lack of fiber was the cause, and the medical profession ran with the hypothesis for decades (and still does: who needs proof?).
However, we know that wheat will adversely affect the lining of the gut, including the colon, and can also increase fecal volume. My doctors told me that I wasn’t eating enough fiber after my second acute attack. So I started eating more. Lots of whole wheat, and salad with seed oils. Several months later, as my diverticulitis continued to get worse, I had surgery.
Two years later I stated reading Stephan Guyenet’s blog. Stopped eating seed oils. I stopped craving carbs, and, by accident, stopped eating wheat. After 16 years, all my symptoms of diverticulitis ceased in two days. As my gut started healing, ingesting even minute amounts of wheat would cause cramping at the site of my resection, and a reemergence of my diverticulitis symptoms.
I have no doubt now that, at least in my case, diverticulitis was caused by wheat consumption, which was exacerbated by the inflammatory effect of seed oils. I know a few other individuals in the same situation who had the same effect. One colleague was saved from a colon resection after he told the hospital to put him on a gluten-free diet while he was in the hospital awaiting surgery. His symptoms resolved in days, and he walked out without needing the surgery.
Can someone with mild Crohn’s disease consume prebiotics and soluble fibre? I had a small bowel resection 8 yrs. ago , and have tried Gaps / Scd diets on and off with limited success…
I love you Chris Kessler! You just reiterated why and how my current way of eating works for me. I have pyroluria. Before I was diagnosed and treated I had diverticulitis. The doctor told me, without even asking what my diet included, to avoid cheese and eat more fiber. He couldn’t have been more wrong. Raw cheese suits me fine but fiber from grains makes me toxic. I’ve had a laundry list of health issues that have been cleared up with GAPS diet, proper supplementation, and now finding Dr. Paul Jaminet’s work which work brilliantly for me.
I’m at the point that I go to the doctor for tests and then find people like you to get real results. It seems we should almost do the opposite of what mainstream medicine says to do.
“kresser.” love starts with the name
I’m married to a wonderful dyslexic man. Gave up correcting people long ago:)
Loved the book, Fiber Menace.
Hi Chris,
Thanks for the great article. My husband has very high LDLs (but also high HDLs), to try to lower the LDLs our Drs nutritionist recommended PGx, among other dietary additions (grapefruit, mushrooms, smaller amounts of coconut oil, etc). What’s your opinion of PGx? It doesn’t really say whether it’s a soluble or insoluble fiber. I took the recommended initial dose myself a few times & it caused gas & bloating but my husband seems to tolerate it well. PGx claims to lower cholesterol and help maintain a healthy weight…your opinion would be greatly appreciated.
Thanks!
Biotagen is FODMAP heavy. How about squashes like butternut and kabocha for those of us who are avoiding FODMAPs and still looking for fiber?
They don’t have as much fiber as the starches and FODMAPs, which is why they’re better tolerated by people with FODMAP or starch intolerance. But they’re a good choice. Can you tolerate starch?
I feel your pain, Eric… literally! I have problems with almost all “prebiotic” fibers including sweet potatoes and winter squash. I heard about a study showing high butyrate production from the resistant starch in cold cooked potatoes only to discover that it’s cold potatoes that make me sick – hot potatoes are no problem!
I’ve been wondering for a while – how does the butyrate content of ghee compare to butter oil? We use ghee all the time, and I’ve started snacking on it. Our family has established that ghee is worth the money. But those butter oil supplements are expensive, and I want some assurance that it would be worth something over and above what we already get from ghee.
So I think this article answers my question. If I am on a vlc diet due to blood sugar issues, then it would be a good idea to supplement? I was told by a chirpractor that is an integrative practitioner to taking fiber would stablize my blood sugar so it is more even. I have lowered my A1c from 11.9 to 5.6 with diet alone. Unfortunately, the fiber supplement has pectin and guar gum.
The fiber supplement he sold me has pectin and quar gum is what I meant to say.
Interesting article! So where does this put your recommendation on aiming for the brown business at the tail end of the tract? Sink or float?
Chris,
Speaking of fatty acid synthesis being important for gut and metabolic health: https://news.wustl.edu/news/Pages/23409.aspx
Hi Chris,
Stephan mentioned that our gut bacteria produce butyrate from both soluble and insoluble fiber. Is the focus on soluble fiber due to a higher rate of conversion into butyrate?
Yes, soluble fibers have a greater impact on SFCA production.
You’ve missed a really critical factor about fiber – it is not one ingedient or one type of ingredient. It is a class of ingredients that has very very different effects. Researchers are now talking about dietary fiber in terms of 3 mechanisms – bulking, viscosity and fermentation. Bulking fibers hold a lot of water and are excellent for regularity – i.e., wheat bran, cellulose and psyllium. Viscous fibers thicken the contents of the intestinal tract and help to lower the absorption of cholesterol and glucose – i.e., beta glucan, psyllium. Finally, some fibers are fermented (unlike wheat bran, cellulose, psyllium which are minimally or not fermented at all). The fermentation produces the short-chain fatty acids. Each fiber produces a different range of short-chain fatty acids (depending on the bacteria that are doing the fermenting and the type of fiber). For instance, resistant starch produces the most butyrate, while inulin and fructo-oligosaccharides (FOS) produce the least. A lot of research is occurring to identify the health consequences of this biochemical cascade. Inulin is fermented very quickly – which tends to cause gas, bloating and cramping. You can’t assume that fiber is fiber – a tremendous amount of data is proving that nothing could be further from the truth.
Each persons digestive tract will have its own characteristics – how you can tolerate fermentation, the composition of your microbiota, etc. I’m not an expert on disease conditions of the intestinal tract, but I know that different fibers have very very very very very different effects and that your analysis lumping them all together is terribly out-dated.
Thank you Rhonda W,
I will begin adding plenty of wheat and cardboard to my diet.
Why would you add cardboard to your diet? And wheat bran is mostly good for constipation. I’d go for fermentable fibers from foods or supplements. It’s the fermentation which produces butyrate and other short-chain fatty acids. And solubility doesn’t determine whether a fiber is fermented or not. One paper found that insoluble resistant starch produces more butyrate than other types of fermentable fibers. (Cummings JH, Macfarlane GT, Englyst HN. “Prebiotic digestion and fermentation” Am J Clin Nutr 2001;73(suppl):415S–20S.) Soluble oligofructose produces the least amount of butyrate. Other studies have found that resistant starch turns on the genes in the large intestine that produce GLP-1 and PYY, which are hormones important in hunger management, insulin sensitivity and carbohydrate metabolism. These hormones may be responsible for the improvements in insulin sensitivity and satiety that have been published with resistant starch. The latest insulin sensitivity study found a 56% improvement in insulin sensitivity in overweight and obese men fed 3 tablespoons of a RS2 resistant starch ingredient. Non-fermentable cardboard and wheat fiber won’t cause changes carbohydrate metabolism – they aren’t fermented. Again – different fibers do very different things.
“You’ve missed a really critical factor about fiber…”
Rhonda, Chris didn’t miss it. It’s in there. You missed it…
“And wheat bran is mostly good for constipation.”
It’s also really good for causing rickets in children.
The point in part of this post, which you also seem to have missed, is that the benefits of fiber have been largely over-sold by docs who came up with a hypothesis but never bothered to test it.
I agree with you that the medical establishment has over-sold fiber. But, don’t throw the baby out with the bathwater (just like Atkins did). Some fibers are incredibly important and have a TON of evidence supporting their consumption, especially when you know enough about fiber to be able to select the ones that will help to address specific conditions.
For instance, Kim was asking about fibers to stabilize blood sugar. Viscous fibers (like guar gum and pectin) make claims that they lower the absorption of glucose and that should mean that it promotes health. There’s a big flaw in their claim – eating lower glycemic foods does not correlate to reduced risk of diabetes. People with healthy levels of insulin sensitivity can handle a wide fluctuation in the glycemic response of their foods. People with insulin resistance are less flexible.
However, one ingredient – RS2 resistant starch – which is regarded as a natural insoluble dietary fiber – has 6 clinical studies showing that it directly improves insulin sensitivity – other fibers don’t do this – especially non-fermentable fibers. Insulin levels are lower beginning 30 minutes after you eat it and lasts into the next day. This absolutely helps to stabilize blood sugar levels and is beneficial. The latest study found a 56% improvement in insulin sensitivity after eating 3 tablespoons of RS2 resistant starch in overweight and obese (but not diabetic) men. Fiber in general will NOT give you this benefit – but resistant starch will.
Animal studies are taking it one step further – two just published showing that when compared to high glycemic starch, RS2 resistant starch reduced lesions, photoreceptor abnormalities and advanced glycation end products – all of which precede age-related macular degeneration (AMD). (Weikel KA et al, Investigative Ophthalmology & Visual Science, 2011.Epub ahead of print December 28, 2011 doi: 10.1167/iovs.11-8545. and Uchiki T, et al. Aging Cell Feb 2012; 11(1):1-13. doi: 10.1111/j.1474-9726.2011.00752.x ) The connection between insulin sensitivity and AMD is very real, and incorporating resistant starch into your diet (if your intestinal tract is healthy enough to manage the fermentation process) improves insulin sensitivity and helps your body manage blood sugar better. The research has been done with the isolated ingredient (which people sprinkle onto their foods, blend into smoothies or oatmeal, etc), or eaten as naturally occurring in foods like beans, under-ripe bananas, and intact whole grains.
Kim should be supplementing with Hi-maize resistant starch, an insoluble type of dietary fiber that is fully fermented, produces the most butyrate of all fibers tested, and significantly improves insulin sensitivity within less than an hour.
Rhonda, it would be good of you to note that you’re a representative of National Starch Co, which makes high-amylose corn starch.
@Rohnda
Thank you for providing additional information.
Chris,
Thanks for the great post! For the past year I have struggled with a C.Difficle infection and I now have post-infectious IBS. I have a very hard time finding a “Happy medium” it is either all flow or no flow and nothing in the middle. The fiber content in my diet something I constantly try to monitor to help maintain healthy bowels. Thanks again for fighting for the little guy.
I chatted with a nutritionist today who stated that fiber rich foods help remove toxins from the body. I know that claim may ring a bit unscientific (it did to me), but I honestly want to evaluate if there is any literature backing that idea. Do you have any opinions on whether this is bogus or legit?
To respond to Morgans’s question, yes, fiber from dark leafy green vegetables can help with a detox regiment to move the bowels. I use a product called Phytogreens by Seroyal and have people add the greens powder to smoothies. The chlorophyll part (found in green plants) helps bind to toxic waste products that come from the liver and the fiber part helps move the bowels. It is used in heavy metal detox protocols, mold detox protocols, candida, and it also helps with decreasing cholesterol. Some of the sickest patients that I see don’t move their bowels regularly.
I say that everything in excess is bad but a diet based on fiber from alkaline foods is the best way to go; after all, the body needs to be in the alkaline state in order to be healthy (PH between 7.35 – 7.45) and a fiber intake of about 25 gr/day.
I thought acacia was an allergen – or is it just its pollen?
I have a friend who was on standard american diet growing up, never liked vegetables as a kid, etc, etc, etc. Then after she got married and had children, she really got into taking care of her and her family’s health, proper nutrition, etc. Gradually, they started to eat more and more vegetables, berries, nuts, seeds and other high-fiber content foods. When she turned 35, she was taken to a hospital with a terrible bout of diverticulitis, which came as shock to everyone because she is so young and they all ate so healthy. Now she has to stay away from fiber and a lot of foods that are good for healthy people but not for somebody with her condition. Anything that has seeds of some sort in it causes flare-ups now. She can eat only very little of fiber and has to be very selective with the source. I was wondering if Mr. Kresser would have some thoughts on it, recommendations or a link to diverticulitis diet. Just trying to help my friend!
Hi: I am interested in understanding Pysillum Seed/husk. I am on the SCD diet and they do not like Pysillum because they believe it may be feeding the bad bacteria along with the good.. This is what they say on the website “Pysillum are loaded with cellulose and lignin which some bacteria thrive on. We accept that the cellulose in vegetables and fruit can be handled OK but a concentrated form such as husks would not be in order.” So, does that mean none should be eat at all. For instance I noticed that some recipes are including small amounts of Pysillum to bind together the flours they are using. The Julian Bakery makes a Paleo Coconut Bread made from Coconut flour and the use Pysillum to bind the Coconut flour. Sort of like using “Gums” which you also mentioned above. I personally cannot use any gums. So, the Pysillum is interesting, but I don’t want to use if it’s going to cause an over growth of bad bacteria. Or a problem with not absorbing the nutrients I need from important foods I am eating. I’ve heard that is a problem too. Anyway,, could you please explain to me if Pysillum is safe to use and why for binding baked goods such as bread. Thank you for your help, Cathi G. Ventura, CA
Hi Mr. Kresser,
I was just wondering what your thoughts are on coconut meat, which contains loads of fiber. I’m living a paleo diet lifestyle, and I’m very interested in knowing if this is a food that will be hazardous to my GI health (I eat about 200g/day of coconut meat). I know that you are a busy man, so a simply smiley would suffice if the fiber from a coconut is of benefit.
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