Saturday, September 30, 2017

Important Heath Effects of Dietary Fiber

Dietary fiber consists of non-starch polysaccharides (NSP) and many other plant components such as resistant starch, resistant dextrins, inulin, lignin, chitins, pectins, beta-glucans, and oligosaccharides.

Dietary fiber can contribute to your overall good health and longevity, and can have a positive impact on lowering risk of diseases related to Western diets, which include:[1]
  • Cancers[25,26]
  • Diabetes[27]
  • Tumor formation
  • Disordered laxation
  • Autoimmune diseases
  • Coronary heart disease[28]
  • Inflammatory bowel disease
  • Mineral related abnormalities
by feeding and promoting healthy gut bacteria.

In this article, we will cover the health effects of fiber from two prospectives:
  • Traditional wisdom 
    • Mostly from digestive system perspective
  • Gut Microbiota 
    • Mostly from immune system perspective

Traditional Wisdom

Proven benefits of dietary fiber include fewer colon polyps and thus less risk of colon cancer.  Dietary fiber is also thought to help prevent iron overload, which could promote inflammation in the colon that leads to mucosal damage, since fiber binds to iron and helps the metal pass out of the body through the digestive tract.[5]
  • Insoluble fiber
    • Insoluble fiber you consume is passed through your gut undigested and sweeps out it like a broom
    • Benefits
      • It is an effective laxative to relieve your constipation or irregular stools
  • Soluble fiber
    • Soluble fiber attracts fluid in your gut, creating a slow-moving gel
    • Benefits
      • It slows digestion, which allows vitamins and minerals to absorb through intestinal walls
        • For example, daily consumption of dietary fiber significantly increases calcium absorption and enhances bone mineralization during pubertal growth[11]
      • It can help lower plasma cholesterol levels and help to normalize blood glucose and insulin levels

Gut Microbiota

Intestinal epithelial barrier

The total surface area of the gastrointestinal system is approximately 300 to 400 sq. m.  However, only a single epithelial layer separates you from enormous amounts of antigens of both dietary and microbial origin.

Sitting on top of this cell lining is a layer of mucus that is also an important part of the intestinal epithelial barrier. This barrier's job is to regulate everything that passes between your intestine and the rest of your body.

Together with the immune cells located in your gut, which represents almost 70% of the entire immune system, the barrier helps control how your immune system reacts to anything foreign. When the barrier is weak or comprised, you have a condition called leaky gut syndrome which can potentially increase your risk of autoimmune diseases.

Short-chain fatty acids

Dietary fiber can be fermented into short chain fatty acids (SCFAs) in your guts. SCFAs have a number of health promoting effects:[1,14]
  • Lowering the pH of the colon
  • Inhibiting growth of pathogenic organism
  • Increasing mineral absorption
  • Serving as a vital fuel source for the colonic epithelium and key regulators of immune homeostasis
    • Which serves as the prototypical example of the symbiotic nature between the microbiome and the host in terms of diet and metabolism
Of the SCFAs, butyrate is considered to be the preferred fuel of cells of colon (i.e. colonocytes).  Without butyrates for energy, colon cells can undergo autophagy (self digestion) and die.[18]

Beneficial gut bacteria
Most gut bacteria reside only in the colon (which has a volume of 0.4 liters). SCFAs are produced by these beneficial colonic bacteria (probiotics) that feed on, or ferment prebiotics, which are plant products that contain adequate amounts of dietary fiber. 
In the video above, Dr. Sonnenburg found that microbes in the guts of Americans make more enzymes that degrade mucins, compared with those in the Hadza who still lead a historic hunter-gatherer way of life in Tanzania. These enzymes allow bacteria to harvest carbohydrates from the mucosal lining of the gut, rather than from plant fiber.[20]
In other words,
If you’re not feeding your gut microbiome with dietary fiber,” Dr. Sonnenburg said, “your gut microbiome is literally feeding on you,” 
which may result in changes in microbiota localization and barrier disruption in the distal gut. Interactions between resident microbes and host leading to immune dysregulation may explain several diseases that share inflammation as a common basis. 
Besides serving as foods to colonic bacteria, scientists have also found that polyphenols bound to the fiber may have a significant physiological impact within the large intestine, affecting microflora development and intestinal antioxidant status by producing metabolites that can be absorbed through the mucosa.[13]

Sources of Dietary Fiber 

In recent years, it become clear that in order to be truly healthy, you need a healthy gut. Dietary fiber is used as food for your beneficial bacteria, and a healthy microbiome is essential to optimizing your health. For example, they produce compounds that help regulate your immune function and even improve brain health.
Dietary fiber can be found from the following food sources:
  • Insoluble fiber 
    • Blackberry seeds, celery, dark-green leafy vegetables, green beans, skins of onions, and whole grains
  • Soluble fiber
    • Apples, barley, beans, berries, citrus fruits, cucumbers, oats, nuts, peas and psyllium.
Note that many whole foods contain both soluble and insoluble fiber.  Dr. Mercola recommend consuming a minimum of 35 grams of fiber and ideally > 50 grams from whole foods per day.[12] Also, be warned that your gut may not be used to these amounts of fiber, you will want to gradually increase to those levels, as they can cause gas and bloating and even constipation until your microbiome readjusts.


  1. V Kumar, A K Sinha, H P Makkar, G de Boeck, K Becker. Dietary roles of non-starch polysaccharides in human nutrition: a review. Crit Rev Food Sci Nutr. 2012;52(10):899-935
  2. How The Gut Microbiota Affects Our Health with Dr. Erica & Dr. Justin Sonnenburg
  3. Gut Bacteria Can Fluctuate With the Seasons
  4. Paleopoo: What We Can Learn from Fossilized Feces
  5. Why You Should Always Use Organic Red Onions
  6. J. I. Wurzelmann et al., "Iron Intake and the Risk of Colorectal Cancer," Cancer Epidemiology, Biomarkers and Prevention, 5, no. 7 (July 1, 1996): 503-7.  PMID: 8827353.
  7. Justin Sonnenburg on "The Good Gut"
  8. Mucins in the mucosal barrier to infection
  9. Scientists bust myth that our bodies have more bacteria than human cells
  10. Dr Greger on dietary fibers
  11. S A Abrams, I J Griffin, K M Hawthorne, L Liang, S K Gunn, G Darlington, K J Ellis. A combination of prebiotic short- and long-chain inulin-type fructans enhances calcium absorption and bone mineralization in young adolescents. Am J Clin Nutr. 2005 Aug;82(2):471-6.
  12. Fat for Fuel (Dr. Mercola)
  13. F Saura-Calixto. Concept and health-related properties of nonextractable polyphenols: the missing dietary polyphenols. J Agric Food Chem. 2012 Nov 14;60(45):11195-200.
  14. J R Goldsmith, R B Sartor. The role of diet on intestinal microbiota metabolism: downstream impacts on host immune function and health, and therapeutic implications. J Gastroenterol. 2014 May;49(5):785-98.
  15. The Good Gut: Taking Control of Your Weight, Your Mood, and Your Long-term Health
  16. Justin Sonnenburg and Erica Sonnenburg Publications
  17. Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates
  18. Donohoe, Dallas R.; Garge, Nikhil; Zhang, Xinxin; Sun, Wei; O'Connell, Thomas M.; Bunger, Maureen K.; Bultman, Scott J. (2011). "The Microbiome and Butyrate Regulate Energy Metabolism and Autophagy in the Mammalian Colon". Cell Metabolism. 13 (5): 517–26. 
  19. Lupton, Joanne R. (February 1, 2004). Microbial Degradation Products Influence Colon Cancer Risk: the Butyrate Controversy. vol. 134 no. 2: J. Nutr. pp. 479–482.
  20. Sonnenburg JL, Xu J, Leip DD, Chen CH, Westover BP, Weatherford J, Buhler JD, Gordon JI. Glycan foraging in vivo by an intestine-adapted bacterial symbiont. Science. 2005;307:1955–1959.
  21. ‘Ridiculously Healthy’ Elderly Have the Same Gut Microbiome as Healthy 30 Year-Olds
  22. Gut microbes could help trigger multiple sclerosis
  23. Constipation and Its Remedies (Travel and Health)
  24. Which Food Fights Cancer Better? (Travel to Health)
  25. Aune D, Chan DS, Lau R, et al. Dietary fibre, whole grains, and risk of  colorectal cancer; systematic review and dose-response meta-analysis of prospective studies.  BMJ. 2011;343:d6617.
  26. Aune D, Chan DS, Greenwood DC, et al.  Dietary fiber and breast cancer risk: a systematic review and meta-analysis of prospective studies.  Ann Oncol. 2012;23(6):1394-402.
  27. Yao B, Fang H, Xu W, et al.  Dietary fiber intake and risk of type 2 diabetes: a dose-response analysis of prospective studies, Eur J Epidemiol. 2014;29(2):79-88.
  28. Threapleton DE, Greenwood DC, Evans CE, et al. Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis. BMJ. 2013;347:f6879.

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