Dietary Fibre and Short Chain Fatty Acids 101

fiber short chain fatty acids health and disease gut health specialist SIBO specialist klebsiella citrobacter blastocystis naturopathic treatments

Dietary fibre and the short chain fatty acids that are produced as a by-product have many beneficial impacts on human health. For years now I have been writing on the benefits of different short chain fatty acids (butyrate, acetate and propionate) for gut health and the treatment of many gut conditions. Today we will be covering what exactly these short chain fatty acids are, which bacteria produce them and how they help to create a healthy gut ecosystem. 

You could spend your entire career exploring the production and effects of short chain fatty acids in the human digestive tract. In fact, people have done so. This article is intended to be an introduction to the ideas and is not intended to be a deep dive into the subject at hand.

Ok, now that little disclaimer is out of the way, onwards.  

Gut Health. It’s all about balance

Today we are talking about short chain fatty acids, produced by bacteria with the consumption of dietary fibre, prebiotics and starches. 

If you struggle to consume foods that contain these and experience symptoms such as bloating, nausea, abdominal pain, brain fog or aching joints, you may be suffering from underlying gut dysregulations such as SIBO, large bowel infections or bacterial overgrowths or even leaky gut

If you are looking for help treating these issues please get in touch with us at Byron Herbalist and we will see if we can help.  

What are short chain fatty acids?

Short chain fatty acids are the metabolites – the byproducts if you will – of fiber fermentation by bacteria in the gut. More on that later. The three short chain fatty acids that we will be talking about include butyrate, acetate and propionate. These make up over 95% of the short chain fatty acids in the gastrointestinal tract (1).

Butyrate.

This is the most well studied short chain fatty acid with numerous health benefits that we will cover shortly. It is produced by a number of bacteria including 

  • Roseburia spp
  • Eubacterium rectale
  • Eubacterium hallii
  • Coprococcus eutactus
  • Clostridium leptum
  • Faecalibacterium prausnitzii
  • Eubacterium rectale
  • Anaerostipes caccae
  • Coprococcus catus
  • Subdoligranulum

Acetate.

This particular short chain fatty acid is produced by a range of bacteria in the gut including 

  • Lactobacillus spp., 
  • Bifidobacterium spp.
  • Akkermansia muciniphila
  • Bacteroides spp.
  • Prevotella spp.
  • Ruminococcus spp.
  • Streptococcus

Propionate.

Propionate is produced by 

  • Phascolarctobacterium succinatutens
  • Bacteroides spp.
  • Dialister spp.
  • Megasphaera elsdenii
  • Veillonella spp.
  • Coprococcus catus
  • Roseburia inulinivorans
  • Ruminococcus obeum
  • Salmonella spp

Production of Short Chain Fatty acids from fibre

To be clear we are only talking about short chain fatty acid production in the gut. This is the result of the fermentation of fibre mainly. Fibre is difficult for us to digest. We leave that job to the bacteria that live in our intestinal tract. Most fibre makes its way to the large intestine where they can be utilised by different types of beneficial bacteria as food. This process, called bacterial fermentation, results in the production of different short chain fatty acids (2).

As a nice little example here. The human genome encodes for 17 glycoside hydrolases (enzymes that aid in the digestion of carbohydrates). Different Bifidobacteria species, such as B. longum, contain up to 56 genes that encode glycoside hydrolases (3).

Fiber is difficult to define. Erica and Justin Sonnenberg, Stanford University researchers, help to narrow down some working definitions in their paper – Starving our Microbial Self:The Deleterious Consequences of a Diet Deficient In Microbiota-Accessible Carbohydrates

First we have dietary fiber, which doesn’t mean much. The attempt to divide soluble fiber into insoluble fiber to distinguish between fiber that can be fermented by bacteria into fiber that cannot doesn’t hold up either – for awhile it was thought that only soluble fiber could be used by bacteria as food. 

The Sonnenburgs have come to the term MACs, or microbially accessible carbohydrates to define a type of carbohydrate that bacteria can use as food. 

The image they provide below is a great summary of their working theory on the benefits of fibre on human health and disease. 

Image taken from: Starving our Microbial Self:The Deleterious Consequences of a Diet Deficient In Microbiota-Accessible Carbohydrates.

Their theory, outlined in the image above goes like this. 

  1. Traditional populations ate a much larger amount of microbially accessible carbohydrates (think fiber here) compared to industrialised populations (think of the standard american diet aka the SAD diet here)
  2. This large amount of microbially accessible carbohydrates would in turn feed bacteria in the gut and increase the amount of short chain fatty acids. 
  3. This abundance of short chain fatty acids would then go on to impart health benefits and protect against western diseases. 

This is a theory they have been working on for quite some time and they have produced countless scientific papers helping to flesh out the details. You can check out more of their work here and here.

An example of increased consumption of microbially accessible carbohydrates in traditional cultures is baobab that is consumed year round by the Hadza. The Hadza are one of the last few hunter-gatherer cultures residing in Tanzania, Africa. The baobab, along with the fiber rich tubers, leads to an incredibly fiber rich diet, especially when compared to industrialised diets (5).

So a nice little summary here is that dietary fiber (or more specifically microbially accessible carbohydrates) can be used as a food source for different bacteria which then produce short chain fatty acids. 

Short Chain Fatty Acids and Health

Most researchers would agree that dietary fiber is beneficial. High level science (systemic reviews with meta analysis take a collection of studies that have been evaluated for quality and assess the combined outcomes) has shown again and again that dietary fiber is helpful indlucing

  • 2019 systemic review with meta analysis showing a deduction in rectal cancer of up to 20% (6).
  • 2018 systemic review with meta analysis showed soluble fibre could reduce blood pressure (7).
  • 2018 review of systemic reviews with meta analyses concluded that a high fiber diet is helpful in a range of diseases including cardiovascular disease, type 2 diabetes and pancreatic cancer (8).

The list could go on and on. Maybe an article devoted solely to dietary fibre would be helpful. 

But what does dietary fibre have to do with short chain fatty acids and their health promoting effects? 

The short chain fatty acids being produced from the dietary fibre being fermented by the beneficial bacteria in our gut may be the real driver of many of the benefits of fibre. 

Put another way. Fibre may be, in part, so important for human health because it is the main food source for bacteria which then produce short chain fatty acids. To be fair not all fibre can be fermented by these bacteria and fibre does have other benefits including bulking of the stool (thus decreasing constipation and straining).

Side note: This is why I like to include well tolerated fibres when I am treating methane dominant SIBO. You can learn more about my approach to that here.

Image taken from: From Dietary Fiber to Host Physiology: Short-Chain Fatty Acids as Key Bacterial Metabolites

Benefits of Short Chain Fatty Acids

In general short chain fatty acids can impart health benefits in a number of different ways. They can 

  • Decrease colonic pH
  • Inhibit the growth of pathogens
  • Improve integrity and function of colonic epithelial cells
  • Have anti-lipolysis effects
  • Increase insulin sensitivity 
  • Increase energy expenditure
  • Inhibit production of proinflammatory cytokines. 

Each of the three short chain fatty acids have their own effects, shown in the table below.

Image taken from: Bifidobacteria and Butyrate-Producing Colon Bacteria: Importance and Strategies for Their Stimulation in the Human Gut  

Butyrate.

Let’s start with butyrate as it is the best studied and most impactful short chain fatty acid. 

Butyrate is amazing. It has been shown to confer health benefits in a number of different ways. 

In the intestinal environment butyrate 

  • Is the preferred energy source for the colon epithelial cells 
  • Decreases the pH of the colon (which decreases bile salt solubility, increases mineral absorption, decreases ammonia absorption, and inhibits the growth of pathogens)
  • Stimulates proliferation of normal colon epithelial cells 
  • Prevents proliferation and induces apoptosis of colorectal cancer cells 
  • Affects gene expression of colon epithelial cells 
  • Plays a protective role against colon cancer and colitis
  • Improves the gut barrier function by stimulation of the formation of mucin, antimicrobial peptides, and tight-junction proteins 
  • Interacts with the immune system 
  • Has anti-inflammatory effects 
  • Stimulates the absorption of water and sodium 
  • Reduces oxidative stress in the colon 

Butyrate has also been shown to have beneficial systemic effects. It is hard to tease out whether these beneficial effects are simply from improved gut health or if excess butyrate makes it into the bloodstream. 

Let me explain by using an example of how butyrate can help prevent cardiovascular disease simply by improving the gut wall. 

Certain bacteria in the large bowel ferment dietary fiber and produce butyrate. We’ve covered that already. Butyrate has been shown to enter the cells that line the gut (called colonocytes). Here they upregulate tight junctions which keep the gut barrier nice and tight and functioning properly. This keeps less-friendly bacteria’s by-products such as endotoxin (also known as lipopolysaccharide or LPS) from entering the bloodstream and causing the inflammatory cascade that leads to atherosclerosis (10).

If you are more of a visual learner I have included a graphic from the paper that outlines the process described above. 

Image taken from: Bacterial butyrate prevents atherosclerosis  

Butyrate producing species have also been shown to be reduced in Crohn’s disease patients (11).

Butyrate production may help improve sleep – animal study (12).

Butyrate may help increase bone mass (think osteoporosis) by upregulating T-regulatory cells which trigger a cascade of cell responses (involving transforming growth factor beta, Wnt10b and cytotoxic T cells) that leads to increased bone building rather than breaking down – in vivo study (13).

Image taken from: Make (No) Bones about Butyrate  

Acetate. 

Acetate has beneficial effects on the intestinal environment. It can 

  • Be used as an energy source for the cells that line the colon 
  • Decrease the pH of the colon – This increases mineral absorption, decreases ammonia absorption, inhibits pathogen growth) 
  • Is anti-inflammatory 
  • Increases colonic blood flow and oxygen uptake
  • Can be used as a substrate by other bacteria to make butyrate

The last point, that acetate can be used by bacteria to make butyrate is something that I have been fascinated by. This concept touches on the cross-feeding theory which I absolutely love. 

The best way to describe cross-feeding is by using Bifidobacteria as an example. 

Bifidobacteria is thought to be a beneficial bacteria. I’m not a researcher so I’ll go out on a limb and call it beneficial. There is ample evidence to support this statement!

Feeding up Bifidobacteria in the large bowel is simple enough. It is considered a primary decomposer and can ferment and grow on many different types of starches, fibres and prebiotics

Bifidobacteria produces the short chain fatty acid acetate, which along with its other benefits on human health can also be used as a substrate by other bacteria to produce the amazing butyrate. Bifidobacteria also liberates the tough to consume foods for these beneficial bacteria to consume as well. 

There are a number of different types of cross-feeding but the end result is the same. Bifidobacteria growth produces substrates that other beneficial bacteria need to grow and produce other helpful short chain fatty acids.

Image taken from: Bifidobacteria and Butyrate-Producing Colon Bacteria: Importance and Strategies for Their Stimulation in the Human Gut  

Propionate. 

Finally propionate has intestinal effects including 

  • Is a minor energy source for the colon epithelial cells 
  • Decreases the pH of the colon (which decreases bile salt solubility, increases mineral absorption, decreases ammonia absorption, and inhibits the growth of pathogens)
  • Prevents proliferation and induces apoptosis of colorectal cancer cells 
  • Interacts with the immune system 
  • Has anti-inflammatory effects 

Systemically its effects include 

  • Promotion of satiety 
  • Lowers blood cholesterol levels
  • Decreases liver lipogenesis 
  • Improves insulin sensitivity 

That is a pretty impressive list. Each of these points are specific treatment outcomes in a range of gut treatments. 

One that jumps out to me and my interest in gut infections is the point that different short chain fatty acids can inhibit the growth of pathogens.

How short chain fatty acids inhibit the growth of pathogens

Hundreds of people have been in touch with me regarding their gut health issues. 

One approach that many of these people have taken (under the guidance of a clinician or self-directed) is the direct antimicrobial approach. For each one of these individuals this approach has, at least in part, failed.

Here the concept of the gut ecosystem and short chain fatty acid production comes into play again (my favourite subject). When treating bacterial overgrowths and infections, short chain fatty acid stimulation can help to balance the ecosystem, shifting the ecosystem in a particular way that inhibits pathogens.

Any questions or comments? Leave them in the comment section below

References and Resources

  1. Gut Microbiota, Short-Chain Fatty Acids, and Herbal Medicines
  2. From Dietary Fiber to Host Physiology: Short-Chain Fatty Acids as Key Bacterial Metabolites
  3. Bifidobacteria and Butyrate-Producing Colon Bacteria: Importance and Strategies for Their Stimulation in the Human Gut  
  4. Starving our Microbial Self:The Deleterious Consequences of a Diet Deficient In Microbiota-Accessible Carbohydrates
  5. Seasonal Cycling in the Gut Microbiome of the Hadza Hunter Gatherers of Tanzania
  6. Rectal Cancer: 20% Risk Reduction Thanks to Dietary Fibre Intake. Systematic Review and Meta-Analysis
  7. The effect of viscous soluble fiber on blood pressure: A systematic review and meta-analysis of randomized controlled trials
  8. Dietary fiber and health outcomes: an umbrella review of systematic reviews and meta-analyses
  9. From Dietary Fiber to Host Physiology: Short-Chain Fatty Acids as Key Bacterial Metabolites
  10. Bacterial butyrate prevents atherosclerosis  
  11. Reduced Abundance of Butyrate-Producing Bacteria Species in the Fecal Microbial Community in Crohn’s Disease
  12. Butyrate, a metabolite of intestinal bacteria, enhances sleep
  13. Make (No) Bones about Butyrate

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