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Dietary Fibre, Prebiotics & SCFA's

What does dietary fibre, as a source of prebiotics, and subsequent short-chain fatty acid (SCFA) production, do for us? Let's discuss the components individually first, and then address the benefits.


Dietary Fibre

Dietary fibre is the indigestible parts of plant foods that we eat. There are different categories of dietary fibre.


1. Soluble fibre

Forms a gel and acts on our stomach to swell and make us feel full longer, and on our bowels to smooth the passage. It also stabilises our blood glucose and cholesterol levels. Example include: fruits, vegetables, and lentils.


2. Insoluble fibre

Keeps our bowels moving by making its way through to our large intestine (colon), where it absorbs water, swells and brings on the peristaltic wave-like motion, that will eventually trigger a poop. Examples include: wholegrain foods, nuts, seeds and the skins from fruits and vegetables. Insoluble fibre also feeds the bacteria present inside our large intestine (or colon), and those bacteria then generate SCFA's. We can tell if someone is deficient in SCFA's by having a microbiome sample (poop sample) reviewed. We don't want to be deficient in SCFA's, as we can get ongoing health issues.


3. Resistant Starch

Another class, not classified as fibre but acts like it, is Resistant Starch. It acts similarly to Insoluble Fibre, making its way to the colon for its effects to be seen. Here it ferments, and produces healthy bacteria - this is bacteria 'being in the right place, at the right time.' Examples include: rice and potatoes that have been cooked, cooled, then reheated again. Easy hey? Also undercooked pasta, under-ripe bananas, breads, legumes and oats.


We need to be eating all different types of fibre discussed for our health. It's important to be drinking water as well when eating fibre, else you can become constipated. The important point when eating fibre, is to have small amounts from lots of varied sources. This is where the topic of choosing 30 different plant foods per week come in. Certain fibre foods are 'favourites' of different healthy bacterial species in our gut microbiome, so you can promote the growth of individual beneficial species by your food choices. You can read more: https://www.m-pathnaturopathy.com.au/post/30-plants-a-week-challenge


Link between Dietary Fibre, Prebiotics and SCFA's


Dietary fibre, provides a source of prebiotic fuel for beneficial bacteria in our gut microbiome. Bacteria present in our large intestine, consume the insoluble fibre and resistant starch. In this way, the fibre is acting as a prebiotic - providing a source of food for bacteria in our digestive system to consume.


While it's not necessary for you to know the names of different types of probiotics, they include: Fructooligosaccharides (FOS), Inulin, Galactooligosaccharides (GOS), Pectin, Resistant Starch (RS), Arabinoxylan (AX), and Proanthocyanin (PAC). Should we get a poop sample back saying you are deficient in a certain beneficial bacteria, or SCFA, we know which foods based on the relevant prebiotic to provide you.


As an aside, it is important to note the difference between a prebiotic and probiotic. Prebiotics are food sources for bacteria, while probiotics are the actual bacteria provided to inoculate your bowel.


The end products of that prebiotic consumption are the Short Chain Fatty Acids (SCFA's), which are very beneficial for us. The SCFA's most commonly seen in our bodies are Acetate, Propionate, Butyrate, and should be in the percentage ratio of 60:20:20 for optimal health.


We can see through the flowchart below, the dietary fibre we begin with, the source of prebiotic provided, and the SCFA generated. We can test for SCFA production, and the types of beneficial and harmful pathogens in a poop sample (along with a lot more valuable information).


Flow chart highlighting foods that are prebiotic food sources to gut bacteria to produce short chain fatty acids
Food sources of prebiotics that when fermented by gut microbes produce SCFA's

What can go wrong?


In some people with Small Intestinal Bacterial Overgrowth (SIBO) which is the major contributor to Irritable Bowel Syndrome (IBS), bacteria present in the small intestine (which shouldn't be there), consume the insoluble fibre on its way to the colon. Through this process, gases are produced that are destructive to our small intestine, and are uncomfortable for the person as they become gassy with abdominal pain. This is bacteria 'being in the wrong place at the wrong time.'


Picture of a colon showing where FODMAP's ferment versus where Resistant starch and pectin ferment
FODMAP foods can cause issues in some individuals

This is not at all a case of fibre being bad for you. In fact, it's the opposite. Bacteria can sneak out of the large intestine where they should be, and into the small intestine where they shouldn't be, if they are starved of food sources beneficial to them, or the food on offer in the small intestine is attractive (too much sugar for example). If you aren't eating enough insoluble fibre or resistant starch this may occur.


We can tell if this issue is impacting on you by performing a SIBO test. You may have an indication yourself if you are gassy after eating meals, or experience pain around where your appendix is located - this is also the junction between the small and large intestine (oleo-caecal valve). If bacteria are present in our small intestine, consuming all sorts of foods, including FODMAP fibre, we can also become deficient in our minerals e.g. iron deficient. See my post in SIBO for further discussion: https://www.m-pathnaturopathy.com.au/post/sibo-what-s-the-story


If you have SIBO or IBS, then the dietary fibre that may not be helpful until rectified, is known as FODMAP foods (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols). If this is the case we have to consume low FODMAP foods for a short period until the bacteria are removed. This needs to be done with the help of a qualified naturopath to avoid fibre and nutrient deficiencies.


Pro-inflammatory and Anti-inflammatory effects on our bodies

Our gut microbiome is full of bacteria that digests proteins and fibres. We need a healthy balance. If we are consuming too much protein, we can have pro-inflammatory effects (not good as shown by red arrows below). We need to balance our protein consumption with fibre to feed the bacteria that will have an anti-inflammatory effect (good as shown by green arrows below). The easy way to consider this is with your dinner plate - 1/3 of your plate for protein and 2/3 of your plate for dietary fibre.

Image shows how ASCFA's are produced from a plant dietand how negative pro-inflammatory molecules are produced from an animal diet
Pro-inflammatory and Anti-inflammatory effects from dietary choices on our bodily systems.

Benefits of a high fibre diet

Adjusting our diets to include benefits from more dietary fibre, include improvements for many chronic disorders like neurodegenerative conditions, obesity, diabetes, immunological conditions, and intestinal disorders. This can be seen with:

  • Daily bowel movements, that are formed - no constipation or diarrhoea.

  • No reabsorption of toxins into our bloodstream for the liver to cope with

  • No 'leaky gut'

  • No Inflammatory Bowel Disease (IBD)

  • Healthy mucosal surfaces including our lungs

  • Insulin sensitive (not resistant) meaning we can regulate glucose well

  • Good moods and brain function

  • Absence of inflammation in your body. We don't want our immune system 'trigger happy' when it's not required, else when it is required the response is so much bigger than normal which presents potentially dangerous consequences.

  • Weight control is good, with minimal central abdominal fat


What we eat influences the gut microbiome enormously. Our gut microbiome loves fibre. Do you have symptoms that are telling you that your food choices aren't the right ones?


Feeling ready for a poop test? I can order functional testing for you to identify how your unique dietary fibre and prebiotic food choices and subsequent SCFA production is impacting on your body. If you would like to discuss this further, then please don't hesitate to make a booking with me.



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