Dietary Fibre

Some people think of fibre as a powder stirred in water to help with evacuation. This cannot be further from the truth. There are countless types of fibre, and they all contribute to a healthy digestive tract and overall health. Fibre definitely helps us to defaecate – no doubt about that! But it does so much more for us beyond number twos!

What is Fibre?

Fibre is a primary component of plant cells walls (1). Therefore, whole plant foods comprising fruits, vegetables, whole grains, legumes, nuts and seeds all contain fibre – of varying types and in varying amounts. Fibre is not digested in the small intestine, instead passing through into the large intestine where it can have varying effects. These include:

• Increasing satiety, making us feel fuller and less inclined to overeat 

• Modulating digestion and slowing transit time – thereby helping to control blood glucose and lipid (cholesterol) levels

• Increasing nutrient absorptive capacity by adjusting colonic pH

• Improving laxation by affecting faecal water and bulk

• Providing substrate for fermentation that feed gut microbes

Western diets are tragically low in fibre (2). In Australia, less than 30% of us meet the “adequate intake” of dietary fibre. Furthermore, this level of intake (25 g for women and 30 g for men) is likely much less than optimal (3). Scientists estimate that ancestral humans consumed over 100 g of fibre a day, and from varied fibrous plants (4). This becomes relevant when we compare the rates of chronic disease in countries that maintain a more traditional high-fibre diet (albeit closer to 50 g a day rather than 100 g). These communities sometimes do not encounter the chronic inflammatory diseases that are so rampant in our society. In fact, when African American participants were placed on a high fibre (55 g a day) diet, they reversed markers of colorectal cancer within just two weeks (5).

We NEED fibre to function properly!

There are generally two types of fibre: soluble and insoluble. Whole plants contain both - but in varying quantities. Insoluble fibre helps with laxation, and comes out very similarly as to how it went in! Soluble fibre, on the other hand, has a different trajectory. It feeds your good gut microbes, and they feed you right back!

The Gut Microbiota

You may have heard of the gut microbiota or microbiome. Let’s break down what it is. First of all, you may be shocked to hear that we are not simply human. In fact, depending how you look at it, you could say we are barely human. Of all the nucleus-containing cells that encompass us, only 1 in 10 are human (6). That’s right. So what makes up the majority of who/what we are? Microbes. Primarily bacteria, but also fungi, viruses, parasites, and archaea (1).

When you think of microbes, you probably think of hygiene (or lack there of!). But actually, we have evolved with microbes - existing in a delicate balance and harmony. A symbiosis. A classic “you scratch my back, I’ll scratch yours”. These microbes live all over our bodies, but the majority of them live in our colon or large intestine.

We inherit our gut microbiome when we are born from our mothers (7). This occurs via Mum’s microbiota from her gut, vagina (yep, it has one too!), skin, and breast microbiota-s. Furthermore, human breast milk contains compounds that do not provide any nutrition to the child, but rather develop the microbiota (8). These human milk oligosaccharides are highest in colostrum, humans’ (and all mammals’) first food.

Not all microbes are created equal. Some promote health and some promote disease - both within and beyond the digestive system. The key to gut health is a diverse microbiota of many different species, but with an abundance of health-promoting microbes. This allows for balance and harmony, leading to optimal functioning. When the gut ecosystem is outweighed by disease-causing species, this is called dysbiosis (9). Here, many negative outcomes can ensue.

You’ve probably heard of probiotics. Well, you can think of your good gut microbes just like that - microbial species that exert a beneficial effect on your health. However, you may not have heard of postbiotics. These are microbial byproducts. Healthy gut microbes produce byproducts that enhance health, namely short-chain fatty acids (10). They reduce inflammation, decrease risk of colon cancer, and can even enhance brain function.

Bad gut microbes on the other hand, produce substances that promote disease - increasing inflammation, leading to digestive upsets, and even promoting conditions like cardiovascular disease (11). These bad gut microbes are always around, but they are kept at bay when outnumbered by healthy gut microbes.

Your gut barrier is a micro-thin layer separating the contents of your gut from your blood stream. This represents the largest interface you have with the environment. A healthy gut microbe ecosystem keeps this barrier functioning well - preventing bad things leaching out and causing “leaky gut” (12). This is referred to as increased intestinal permeability, and is associated with many ailments including gastrointestinal conditions, but also autoimmune diseases, asthma, and some liver and skin conditions. This is why we need to do what we can to support a healthy gut ecosystem - and thankfully, we can do quite a lot!

Your Gut and Your Health

The phrase “health and disease start in the gut” is really not far-fetched. Your gut is involved in five key body functions:

• Metabolism

• Immunity

• Hormone regulation

• Gene expression

• Cognition and mood

I think we can agree these are pretty important!

Your microbiota ecosystem determines how well each of these aspects of health function. This is why many diseases like type-2 diabetes, cardiovascular disease, cancer, autoimmune diseases, allergies, endometriosis, most intestinal conditions and obesity are linked to dysbiosis (13). While evidence supports the consumption of a highly fibrous diet of early humans, it is also clear that we have co-evolved with these microbes for millions of years - literally since the beginning (14).

A case report highlights the important of the gut microbiota, in which a woman battling an aggressive and persistent intestinal infection, who was always of normal weight (BMI 26), received a faecal transplant from someone who soon after became obese (15). At her 16 month follow-up the patient had become obese (BMI 33), and besides many efforts to lose weight her obesity worsened twenty months later (BMI 34.5). This transference of obesity had been seen in animal studies, but never before in humans. It is now standard procedure to only donate faecal specimens from normal-weight people.

A Fibre-Centric Diet

Good gut microbes thrive on two things - dietary fibre and resistant starch (10). They are their preferred food! These are called prebiotics. Dietary fibre is found in whole plant foods: whole grains, legumes, fruits, vegetables, nuts and seeds.

Not all fibre is the same, and not all good gut microbes eat the same fibre. Therefore, to foster a diverse gut ecosystem, you need to eat a diverse array of plants. It has been shown that plant diversity in the diet determines the health of the gut. One study found that those eating over 30 unique plants a week had the most diverse gut microbiota (16).

Whole grains and legumes appear to have the most microbe-proliferative effects (17). Cooked (boiled) then cooled potatoes, grains and pasta contain resistant starch. This resists digestion in the small intestine, providing a delectable meal for your good gut bugs.

So get out there and diversify your plants, increase your whole grain and bean consumption, and up your fibre! Don’t go too quickly, however. Your gut microbes need time to adjust and adapt so they can provide the tools you need to digest this extra fibre you’ll be eating. If you’re not used to beans - ease into it, build up your tolerance, and get more good microbes on board!

Make a list each week to see how many unique whole plants you and your microbes eat. Can you get over 30?

If you would like guidance to improve your digestive system and reap the benefits of a healthy gut, I am available for nutrition consults. I am also able to support you with many other health and wellness concerns. Click here to find out more.

By Jessica Zabow
Clinical Nutritionist (BHSc)
& Yoga Teacher (RYT500)

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References:

1. Williams, B.A., Mikkelsen, D., Flanagan, B.M., & Gidley, M.J. (2019). “Dietary fibre”: moving beyond the “soluble/insoluble” classification for monogastric nutrition, with an emphasis on humans and pigs. Journal of Animal Science and Biotechnology, 10(45), 1-12. https://doi.org/10.1186/s40104-019-0350-9 

2. Grundy, M. M-L., Edwards, C.H., Mackie, A.R., Gidley, M.J., Butterworth, P.J., & Ellis, P.R. (2016). Re-evaluation of the mechanisms of dietary fibre and implications for macronutrient bioaccessibility, digestion and postprandial metabolism. 116(5), 816-833. https://doi.org/10.1017/S0007114516002610

3. Nutrient Reference Values. Dietary Fibre. (2019). https://www.nrv.gov.au/nutrients/dietary-fibre

4. Leach, J.D. (2007). Evolutionary perspective on dietary intake of fibre and colorectal cancer. European Journal of Clinical Nutrition, 61(1), 140-142. https://doi.org/10.1038/sj.ejcn.1602486

5. Makki, K., Deehan, E.C., Walter, J., & Backhed, F. (2018). The impact of dietary fibre on gut microbiota in host health and disease. Cell Host & Microbe, 22(6), 705-715. https://doi.org/10.1016/j.chom.2018.05.012

6. Sender, R., Fuchs, S., & Milo, R. (2016). Revised estimates for the number of human and bacteria cells in the body. PLoS Biology, 14(8), 1-14. https://doi.org/10.1371/journal.pbio.1002533

7. Dunn, A.B., Jordan, S., Baker, B.J., & Carlson, N.S. (2017). The maternal infant microbiome: Considerations for labour and birth. American Journal of Maternal and Children’s Nursing, 42(6), 318-325. https://doi.org/10.1097/NMC.0000000000000373

8. Wicinski, M., Sawicka, E., Gebalski, J., Kubiak, K., & Malinowski, B. (2020). Human milk oligosaccharides: Health benefits, potential applications in infant formulas, and pharmacology. Nutrients, 12(1), 1-14. https://doi.org/10.3390/nu12010266

9. Lobionda, S., Sittipo, P., Kwon, H.Y., & Lee, Y.K. (2019). The role of gut microbiota in intestinal inflammation with respect to diet and extrinsic stressors. Microorganisms, 7(), 1-17. https://doi.org/10.3390/microorganisms7080271

10. Silva, Y.P., Bernardi, A., & Frozza, R.L. (2020). The role of short-chain fatty acids from gut microbiota in the gut-brain communication. Frontiers in Endoocrinology, 11(25), 1-14. https://doi.org/10.3389/fendo.2020.00025

11. Tang, W.H.W., & Hazen, S.L. (2014). The contributory role of gut microbiota in cardiovascular disease. The Journal of Clinical Investigation, 124(10), 4204-4211. https://doi.org/10.1172/JCI72331

12. Camilleri, M. (2020). The leaky gut: Mechanisms, measurement and clinical implications in humans. Gut, 68(8), 1516-1526. https://doi.org/10.1136/gutjnl-2019-318427

13. El-Salhy, M., Ystad, S.O., Mazzawi, T., & Gundersen, D. (2017). Dietary fibre in irritable bowel syndrome. International Journal of Molecular Medicine, 40(3), 607-613. https://doi.org/10.3892/ijmm.2017.3072

14. Gordo, I. (2019). Evolutionary change in the human gut microbiome: From a static to a dynamic view. PLoS Biology, 17(2), 1-5. https://doi.org/10.1371/journal.pbio.3000126

15. Alang, N., & Kelly, C.R. (2014). Weight gain after faecal microbiota transplantation. Open Forum Infectious Diseases, 2(1), 1-2. https://doi.org/10.1093/ofid/ofv004

16. McDonald, D., Hyde, E., Debelius, J.W., … Knight, R. (2018). American gut: An open platform for citizen science microbiome research. mSystems, 3(3), 1-28. https://doi.org/10.1128/mSystems .00031-18

17. Zinocker, M.K., & Lindseth, I.A. (2018). The western diet-microbiome-host Interaction and its role in metabolic disease. Nutrients, 10(3), 1-10. https://doi.org/10.3390/nu10030365