How Do Plant-Based Diets Affect Our Gut Microbiota? Part Two

In Part One we looked at various aspects of how our intestinal microbiota was affected by the food we put in our mouths, particularly with regard to variations that occur between plant- and meat-based diets and in relation to the macronutrient, carbohydrate. In Part Two, we’ll take a look at the microbial effects of the other two macronutrients:

  • protein, and
  • fat

as well as the following:

  • polyphenols
  • postbiotics
    • SCFAs 1
    • phytoestrogens
    • isothiocyanates
    • aryl-hydrocarbon receptor ligands
    • Coprostanol and secondary bile acids
    • trimethylamine N-oxide (TMAO), and
    • vitamins


In previous blogs 2 3 4 5 , we’ve looked in great detail at the effects of protein (both animal and plant) on human health. Studies mentioned in the latter blogs have shown how consumption of animal protein (especially in large quantities) is associated with a wide range of common diseases.

When it comes to the effects of protein on gut microbes, the majority of studies suggest 6 that plant protein consumption has a strongly positive correlation with improved healthy microbial diversity.

Impact of dietary protein on intestinal microbiota and health outcomes. SCFAs short chain fatty acids, TMAO trimethylamine N-oxide, Tregs T regulatory cells, CVD cardiovascular disease; IBD inflammatory bowel disease. Source: Singh RK, Chang H-W, Yan D, Lee KM, Ucmak D, Wong K, et al. . Influence of diet on the gut microbiome and implications for human health. J Transl Med. (2017).

The following bacteria are commonly increased in number within the gut microbiota of those individuals consuming a high animal protein diet:

  • Alistipes 7
  • Bilophila wadsworthia 8
  • Bacteroides 9
  • Clostridia 10

The latter are bile-tolerant microbes 11 . Bile increases when animal-protein consumption increases, when compared with increased plant-protein consumption, so it’s no surprise that a meat-based diet will mean that bile-tolerant microorganisms will increase in number 12 .

On the other hand, the following bacteria are commonly decreased in number within the gut microbiota of those individuals consuming a high animal protein diet:

  • Roseburia 13
  • Eubacterium rectale 14 , and
  • Ruminococcus bromii 15

The latter are important for metabolising dietary plant polysaccharides 16 . Again, it’s no surprise that these plant polysaccharide-loving bacteria will frequent the guts of plant-eaters.

It’s a zero-sum game

Another factor which needs to be taken into account is that diet is a zero-sum 17 game: the more protein in your diet, the less room there is for healthy plant carbohydrate. The result of this will be a decrease in butyrate-producing bacteria, and thus an increase in the proinflammatory bodily state and an increased risk of colorectal cancer 18 .

When individuals have eaten pea protein, for instance, it’s been shown 6 that there is a corresponding increase in beneficial Bifidobacterium and Lactobacillus, while the pathogenic Bacteroides fragilis and Clostridium perfringens reduce. The result of this is that there is an increase in intestinal SCFA levels (more on SCFAs below). The latter study drew the conclusion that eating plant-derived proteins reduces mortality when compared with eating animal-derived proteins.


Both quantity and quality of consumed fat have been shown 18 to have significant impact on the composition of gut microbiota.

When you eat a plant-based diet (and here we’re talking about whole, unprocessed plant foods), it will be naturally low in fat. This favours the beneficial Bifidobacteria 19 .

Plant-based fats

The fats from a plant-based diet are made up of mainly mono and polyunsaturated fats. On a phyla level, the result of this is that the Bacteroidetes:Firmicutes ratio 20 increases, while on the genera level, lactic acid bacteria (Bifidobacteria and Akkermansia muciniphila) increase  6 .

Nuts about gut bacteria

Previous blogs 21 looked at how walnuts are particularly good plant-based sources of omega-3 fatty acids (the ALA within them being converted to DHA and EPA within our bodies); however, it doesn’t stop there. Walnuts, and other nuts in general, have been shown 22  to increase Ruminococcaceae and Bifidobacteria while, at the same time, decreasing Clostridium species.

Saturated fat & your guts

Whilst coconut contains unusually high levels of saturated fat for a plant food, saturated fat is almost exclusively found in animal foods.

Studies suggest 23 that saturated fat activates systemic inflammation (by inducing pro-inflammatory cytokines such as IL-1, IL-6 and TNF-α) and thus makes us much more vulnerable to systemic infections 24 and metabolic disorders 25 , such as type 2 diabetes and obesity.

Consuming high levels of saturated and trans fats – something increasingly common in the Western diet – increases the risk of cardiovascular disease and has been shown 6 26 to:

  • increase 
    • Bilophila
    • Faecalibacterium prausnitzii 27 , and
    • Firmicutes
  • decrease
    • Bacteriodetes
    • Bifidobacterium
    • Bacteroides
    • Prevotella
    • Lactobacillus ssp. 28 , and
    • Bifidobacterium spp. 29


Polyphenols are secondary metabolites of plants and are generally involved in defence against ultraviolet radiation or aggression by pathogens 30 . These and other naturally occurring plant metabolites in plant foods have been shown to provide cardiovascular protection 6 as well as both anti-inflammatory and anti-pathogenic effects 31 .

In plant foods, polyphenols increase:

  • Bifidobacterium, and
  • Lactobacillus

Whilst all plants have polyphenols, some of the most common polyphenol-rich foods include:

  • fruits
  • seeds
  • vegetables
  • tea
  • cocoa products, and
  • wine *

*N.B. The many negatives associated with alcohol consumption per se (for both gut health 32 and general health 33 ) suggest that the small quantities of polyphenols in wine are insufficient reason to drink the stuff.

Spice up you guts

Spices and herbs are also very high in antioxidant polyphenols 34 , although the quantities that one can consume are, of course, limited.

And, of course, it’s widely known that tea contains high levels of polyphenols (including catechins, theaflavins, tannins, and flavonoids). Tea consumption increases Bifidobacterium and Lactobacillus–Enterococcus spp., something which appears 35 to result in increased SCFA production within human microbiota.


Part One introduced this relatively new term. The postbiotics we’ll look at here are SCFAs, phytoestrogens, isothiocyanates, aryl-hydrocarbon receptor ligands, Coprostanol and secondary bile acids, trimethylamine N-oxide (TMAO), and vitamins.

It’s important to understand the difference between prebiotics 36 /probiotics 37 on the one hand, and postbiotics, on the other. Basically, prebiotics (e.g. indigestible fibre) are put into the mouth and swallowed; probiotics are the microbes themselves which exist within the gut, but can also be consumed as dietary supplements; whilst postbiotics are the products of microbial activity within our guts.

Both prebiotics and postbiotics are, of course, vital for health. And to clarify once again: Probiotics are microbes that exist already in the GI tract, awaiting prebiotics (the substrate or source material). The products resulting from microbial activity are postbiotics – metabolites that research is showing are of fundamental importance for pretty much every functional system within the host (you and me) – from the gut-brain, gut-lung, and gut-liver axes, to immunoprotection 38 and mental health. 39 40 41

The various systems within our bodies are linked with each other via communication mechanisms that stem from the microbial products/metabolites (postbiotics) produced from the nutrients we ingest. As it happens, some products are diet-independent (for instance, lipopolysaccharides 42 , ribosomally synthesised and post-translationally modified peptides 43 etc.). We’ll set aside these diet-independent postbiotics, and look, instead, at the diet-dependent postbiotics mentioned above.

Location, location, location

The complexity of the human digestive system never fails to amaze. Not only do different foods encourage different microbes to produce different end products, but different locations along the intestinal tract result in different bioactive molecules being produced from the different prebiotics and nutrients 39 44 .

Diet & postbiotics

The type of food you eat is shown 45 to determines the range of postbiotic positive health effects that you enjoy, including:

  • local anti-inflammatory and immunomodulatory 46
  • antiobesogenic
  • antihypertension
  • anticholesterolemic
  • antiproliferative 47 , and
  • antioxidant
How postbiotics work

Postbiotic effects derive from a range of factors, including:

  • modulation of gene expression
  • metabolism
  • intestinal function
  • substrate composition
  • microbiota composition

We’ll now look at the most well-known probiotics – i.e. SCFAs, phytoestrogens, isothiocyanates, aryl-hydrocarbon receptor ligands, Coprostanol and secondary bile acids, trimethylamine N-oxide (TMAO), and vitamins.

Short-Chain Fatty Acids (SCFAs)

The SCFAs acetate, propionate, and butyrate are mostly microbial metabolites of fermented fibre and other carbohydrates, although a tiny fraction does derive from proteins. Levels of these SCFAs significantly increases when a person begins to eat a plant-based diet 48 .

One of the roles of SCFAs is to act as a substrate for the maintenance of healthy colonic epithelium 49 . There is a correlation 50 between plant-based food consumption and improved epithelium health. Maintaining this intestinal barrier prevents endotoxemia 51 and subsequent inflammatory effects 52 53 .

Specific gut microbes are predisposed to produce SCFAs, and different bacteria produce different SCFAs, such as:

  • acetate is produced by enteric bacteria 54 , such as:
    • Akkermansia muciniphila
    • Bifidobacterium spp.
    • Prevotella spp., and
    • Bacteroides spp.
  • propionate is produced by:
    • Bacteroides spp.
  • butyrate is produced by:
    • Coprococcus 55 , but mainly by
    • Clostridium Cluster XIVa, IV, and XVI – species positively correlated with plant-food diets

These SCFAs would not be produced (or, at least, not produced in sufficiently high quantities to maintain optimal health) unless a largely or wholly plant-based diet were consumed.

SCFA protection

SCFAs (acetate, propionate and butyrate, in particular), protect against different types of disease, such as:

  • type 2 diabetes 56
  • inflammatory bowel disease 57
  • immune diseases 58
  • immunity against pathogens 55
  • microglia 59 function and maturation/control of blood–brain barrier integrity 60
  • thermogenesis 61 regulation 62
  • preventing/treating NAFLD 63 and obesity 64
Propionate and gluconeogenesis

Gluconeogenesis (GNG) is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates, such as protein and fat – and reverses the energy-production process of glycolysis. It provides the body’s cells with energy if carbohydrate stores are depleted. The SCFA, propionate acts as a gluconeogenic substrate in both the liver and intestine 55 . As well as helping to provide energy stores for the body, SCFAs are increasingly thought to play important roles as signalling molecules 65 .

The beauty of butyrate

A previous blog 66 looked in some detail at butyrate. This SCFA, and the bacteria which produce it, are becoming increasingly accepted 55 as being highly beneficial to human health, including:

  • acting as a major carbon source for colonocytes 67
  • helping to regulate critical intestinal functions, such as 68 69 :
    • intestinal motility
    • mucus production
    • visceral sensitivity
    • epithelial barrier maintenance
    • immune homeostasis, and
    • maintaining the mucosal oxygen gradient 70 71

The foregoing barely scratches the surface of the vast range of functions and interactions of SCFAs; but the take-home message is that diets rich in fibre seem to provide huge benefits to both the intestine and overall health.


Phytoestrogens are plant-derived polyphenols that interact with oestrogen receptors with either agonist or antagonist actions 72 . They are found in various plant foods (e.g. seeds, grains, beans) and are concentrated in flax and soy – and, oddly enough, beer – the reason that beer-swilling men develop man boobs 73 .

Phytoestrogens appear 74 to have significant health-promoting properties. Research 75 76 77 has shown them to be:

  • anticarcinogenic   
  • antidiabetic
  • antiinflammatory
  • antioxidant
  • protective against cardiovascular disease
  • antiobesogenic
  • antidiabetic
  • protective against osteoporosis and amyloid formation 78

Phytoestrogens have around a 1% bioavailability 79 , and so lots of them are able to get down to the gut.  This is important because increasing evidence 80 81 suggests that the above positive health effects are only reached after bioactivation of the polyphenols by gut microbiota.

The players in polyphenol metabolism

As with most aspects of nutritional science, knowledge is limited about how many microbes are involved in polyphenol metabolism. However, the following are currently known 45 81 to be involved in the following process:

  • converting polyphenols to equol 82 , urolithins 83 , and enterolignans 84 :
    • Bifidobacterium
    • Lactobacillus sp.
    • Coriobacteriaceae
    • Clostridium sp.
    • Bacteroides, and
    • Saccharomyces yeast

Coriobacteriaceae, Eubacterium and other species appear to be responsible for various other polyphenol transformations.

It works both ways

There’s a bidirectional relationship between gut microbiota and polyphenols 85 86 . That is, gut bacteria produce microbial metabolites (postbiotics) from polyphenols, and, in turn, these postbiotics act as prebiotics for various gut bacteria. The net result of this postbiotic production (especially the production of urolithins) encourages the growth of Lactobacillus and Bifidobacterium.


Sulforaphane, discussed in detail in a previous blog 87 in relation to the incredible health-giving power of broccoli, is perhaps the most extensively studied isothiocyanate – that is, a compound converted enzymatically from particular plant components called glucosinolates 88 . Isothiocyanates can be derived from cruciferous 89 or brassica 90 vegetables. The latter are rich sources of glucosinolate, the precursor of isothiocyanates.

The following gut bacteria are largely responsible for facilitating the conversion of the glucosinolates in plant foods to the isothiocyanates our bodies need:

  • Escherichia coli
  • certain Bacteroides
  • some Enterococcus
  • Lactobacillus agilis
  • certain Peptostreptococcus spp., and
  • Bifidobacterium spp.

These bacteria secrete their own myrosinase enzyme 91 in order to metabolise the glucosinolates to isothiocyanates 92 .

Health benefits of isothiocyanates

Isothiocyanates are metabolites which are thought  93 94 to have a range of health-benefiting properties, including being:

  • cytoprotective 95
  • anticarcinogenic
  • antioxidative 
  • antitumoural, and
  • antiinflammatory
  • detoxifying

Aryl-Hydrocarbon Receptor Ligands (AHRLs)

In terms of diet, intestinal aryl-hydrocarbon receptor 96 ligands 97  are mainly derived from eating plant food, especially cruciferous vegetables. Once again, gut bacteria are responsible for producing these AHRLs.

Using aryl-hydrocarbon receptors, these ligands are able to promote gut homeostasis and intestinal immune function 98 , as well as xenobiotic 99 detoxification and maintenance of energy metabolism, including lipid metabolism.

AHRLs and fat

A plant-based diet appears to be better at maintaining an appropriate level of AHRLs, while a high-fat diet appears to decrease the number of aryl-hydrocarbon receptor ligands. A decrease in either aryl-hydrocarbon receptors or in the associated ligands appears to compromise the healthy maintenance of intraepithelial lymphocytes 100 and the ability to control microbial load and composition. This can result in increased immune activation which can, in turn, cause epithelial damage 101 .

The result of this negative process can be gut permeability and inflammation. Both of these can promote the development of metabolic syndrome. Interestingly, some research suggests 98 102  that when metabolic syndrome is produced because of this process, the condition can be improved by supplementing the diet with a probiotic – namely, a strain of Lactobacillus.

Coprostanol and secondary bile acids

Dietary cholesterol is only found in animal-derived foods and, when consumed, it gets broken down in the gut by bacteria. The two resulting cholesterol metabolites (postbiotics) are coprostanol 103 and secondary bile acids.

Coprostanol is poorly absorbed by the human intestine after being isolated from cholesterol by several strains of gut bacteria. This is a good thing as far as cardiovascular disease risk is concerned, since it means that serum cholesterol in the host is reduced, with the coprostanol mostly being excreted in faeces rather than being absorbed back into the bloodstream 104 105  .

The situation is somewhat different when it comes to the other cholesterol postbiotic, secondary bile acids. One of the major uses of cholesterol is in the synthesis of bile acids in the liver. Bile acids are, of course, essential for the absorption of fat from the contents of the intestine; however, when the gut microbiota convert the bile acids synthesised from cholesterol into secondary bile acids 106 , they can be absorbed into the bloodstream and find their way into various tissues within the body. This is a problem.

Being hydrophobic 107 , these secondary bile acids are thought 108  capable of causing direct damage to cell membranes and inducing the generation of reactive oxygen species resulting in DNA damage, apoptosis 109 , and necrosis 110 . Additionally, it’s believed 104 44 that secondary bile acids are involved in maintaining the equilibrium of health and disease – being associated with inflammatory bowel disease, colon and liver cancer.

Trimethylamine N-Oxide (TMAO)

Trimethylamine N-oxide (TMAO) is a molecule generated from choline 111 , betaine 112 , and carnitine 113 via gut microbial metabolism. TMAO is associated with cardiovascular and neurological disorders. Carnitine and choline, precursors of TMAO, are mostly found in foods of animal origin (e.g. eggs, beef, pork), with lower amounts found in beans and fish 114 .

Diets containing animal proteins and fats (particularly red meat) tend to have decreased numbers of Bifidobacterium and increased numbers of L-Ruminococcus, Bacteroides, Alistipes, Ruminococcus, Clostridia, and Bilophila. Such diets are associated with elevated levels of TMAO 48 and, thereby, increased risk of cardiovascular disease and inflammatory bowel disease 23 6 .

The reason plant-eaters have a different gut microbiota composition to omnivores is that they have a reduced capacity to produce trimethylamine (TMA), the precursor to TMAO 115 . This reduced capacity appears to be due to both a reduction in the number of enzymes responsible for converting TMA to TMAO and to the general remodelling of gut microbiota that results from eating a plant-based diet.


We finally come to the gut microbiota which are essential for producing and maintaining adequate vitamin levels within our bodies.

Not a lot of people know this, but our gut microbes produce or process several vital vitamins 93 :

  • menaquinone (vitamin K2)
  • thiamine (vitamin B1)
  • riboflavin (vitamin B2)
  • niacin (vitamin B3)
  • pantothenic acid (vitamin B5)
  • pyridoxine (vitamin B6)
  • biotin (vitamin B7)
  • folate (vitamin B9)
  • cobalamin (vitamin B12*)

* N.B. vitamin B12, while being produced by gut bacteria, is not absorbed back in to the body. This means that vitamin B12 needs to be taken as a supplement by vegans and, arguably, by most other people irrespective of their dietary choices. This is discussed in great detail in previous blogs 116 117 118 119 .

Different bacteria possess specific biosynthetic properties for different vitamins, such as:

  • Bifidobacteriumvitamins K, B1, B7, B9, and B12
  • Bacillus subtilis and Escherichia coliriboflavin 120
  • LactobacillusB12, and other B vitamins 121

The latter is by no means a comprehensive analysis of the relationship between intestinal bacteria and vitamin production/processing; but it does provide a brief insight into one more essential role played by the microbes that live within us.

Final thoughts

It’s thought that, on average, around 25% of the plasma metabolites resulting from gut microbial activity are different between omnivores and vegans, with current research consistently indicating that diet is the essential factor for the composition and health of human gut microbiota. In turn, this is vital for metabolising the nutrients we consume into postbiotics that our bodies need.

All known research continues to suggest that a plant-based diet may be the most effective way of promoting a diverse ecosystem of beneficial microbes that can support overall health. Nutrition is a complex field, with inter-individual differences abounding. This means that further research is necessary if we are every going to be able to fully characterise the interactions between microbiome, diet and health.

But, in the meantime, it looks like you’d be doing your overall health a huge favour if you choose to…

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  91. Myrosinase enzymes, such as thioglucoside glucohydrolase, sinigrinase, and sinigrase, is a family of enzymes involved in plant defence against herbivores. Its known biological function is to catalyse the hydrolysis of a class of compounds called glucosinolates. []
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  95. Cytoprotection is a process by which chemical compounds provide protection to cells against harmful agents. For example, a gastric cytoprotectant is any medication that combats ulcers not by reducing gastric acid but by increasing mucosal protection. []
  96. The aryl hydrocarbon receptor is a protein that in humans is encoded by the AHR gene. The aryl hydrocarbon receptor is a transcription factor within cells to regulate gene expression. []
  97. In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. For instance, in protein-ligand binding, the ligand is usually a molecule which produces a signal by binding to a site on a target protein. []
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  99. A xenobiotic is a chemical substance found within an organism that is not naturally produced or expected to be present within the organism. It can also cover substances that are present in much higher concentrations than are usual. []
  100. Intraepithelial lymphocytes (IEL) are lymphocytes found in the epithelial layer of mammalian mucosal linings, such as the gastrointestinal (GI) tract and reproductive tract. []
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  102. Immunol Cell Biol. 2011 Oct;89(7):817-22. doi: 10.1038/icb.2010.165. Epub 2011 Feb 15. Lactobacillus bulgaricus OLL1181 activates the aryl hydrocarbon receptor pathway and inhibits colitis. Takamura T, et al. []
  103. Coprostanol is the major sterol in human faeces, and has been routinely studied as a marker of (modern) sewage pollution in marine and lacustrine sediments. This has led to the search for coprostanol in archaeological soils, in order to detect the presence of faecal material. []
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  106. Secondary bile acids (or salts) result from the secretion of primary bile acids into the lumen of the intestine. Bacteria partially dehydroxylate them and remove the glycine and taurine groups. The primary bile acids, cholic acid and chenodeoxycholic acid, are converted into the secondary bile acids, deoxycholic acid and lithocholic acid, respectively. []
  107. Hydrophobic molecules and surfaces repel water. Hydrophobic liquids, such as oil, will separate from water. Hydrophobic molecules are usually nonpolar, meaning the atoms that make the molecule do not produce a static electric field. []
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  111. Choline is particularly rich in eggs, liver, and peanuts, and is also found in meat, poultry, fish, dairy foods, pasta, and rice. []
  112. Betaine is a metabolite of choline and is a nonessential nutrient found in numerous food sources, including sugar beets, wheat bran, rye grain, bulgar grain, spinach, quinoa, brown rice, sweet potato, turkey breast, beef, veal and some seafood, such as shrimp. []
  113. Red meat contains the highest level of carnitine. It is also found in smaller amounts in chicken, milk and dairy products, fish, beans, and avocado. Vegans tend to get less carnitine from foods, and their bodies usually produce enough naturally without requiring any from their diet. []
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Cows Don’t Eat Grass

Cows don’t eat grass – but the trillions of bacteria living inside each cow’s digestive system do. Okay, I guess I’m being a bit imprecise to say it like this. Perhaps it would be more accurate to say that cows consume the grass (that is, they use their bodies to get the grass into the first of their four stomachs), but it’s the bacteria inside the cow that are then really responsible for breaking down the grass and thereby releasing energy, protein and micronutrients for the cow to use so she can continue her mooing.

Spectrum of life

I understand that this subject is not directly related to WFPBD or human nutrition in general, but the facts about how cows are able to grow so big by just chomping on the green stuff is so fascinating that I simply had to share it with you. And, it could be argued that there is a sort of link up with plant-based diets; after all, we humans exist within the spectrum of creatures that are either totally carnivorous on the one hand, or completely herbivorous on the other. Arguments abound about our precise location within that spectrum, but there’s no doubt about where our bovine brethren and other similar ruminants 1 reside.

Ruminants have four stomachs

Cows (and bulls, of course), let’s say cattle (also sheep and goats and several other animals) are ruminants. A ruminant is sometimes said to have four stomachs; in actual fact, it’s more accurate to say it has a stomach with four compartments:

  • rumen 2
  • reticulum 3
  • omasum 4
  • abomasum 5

Chewing the cud

The cud is described as: “…a portion of food that returns from a ruminant’s stomach to the mouth to be chewed for the second time. More accurately, it is a bolus of semi-degraded food regurgitated from the reticulorumen of a ruminant. Cud is produced during the physical digestive process of rumination” 6 .

So “chewing the cud” is really a process of rechewing the cud to further break down the plant matter and stimulate digestion. This is called ‘rumination‘, and hey presto! that’s why they are called ruminants. The word “ruminant” actually derives from the Latin ruminare, which not surprisingly means “to chew over again”.

Saliva…lots of saliva

When a ruminant eats grass, the grass is chewed and swallowed and mixed with saliva – and if you’ve ever watched a cow eat, you’ll know that they are particularly good at producing a lot of saliva.  This is necessary since the acidity of the digestive fluids in the rumen (the virtual ‘fermentation tank’ where the grass and hay first goes) needs to be offset by the alkalinity of the saliva. This keeps the pH in the right range for fermentation to take place.

The new hay and grasses float in the middle of the Rumen with the gasses floating to the top and the older grasses and hay sinking down.


Anaerobic microbes

The gooey mass travels through the oesophagus and into the rumen. The rumen acts as a fermentation tank since huge quantities of bacteria 7 , protozoa 8 , methanogens 9 and fungi 10 reside in the rumen. These microbes 11 love the anaerobic 12  environment therein, and so create conditions that allow plant matter to be digested without ever rotting as it would if it were in an aerobic environment.

Mutually-beneficial relationship

The grass entering the cow’s digestive system is not really feeding the cow, it’s feeding these microbes which need the nutrients in order to survive. They, in turn, provide their host, the cow, with the nutrition she needs. This is a mutually-beneficial relationship since both the microorganisms and the cow benefit and complement each other.

Enzymes and microbes

Bacteria produce enzymes 13  to break down the cellulose and hemicellulose 14  in the plant material, which is called cellulase 15 . The microorganisms do this to release the nutrients contained therein so that they can survive and produce the next generation of microbial life.

VFAs (volatile fatty acids)

As the bacteria digest the plant matter, they produce by-products including VFAs (volatile fatty acids) 16 , carbon dioxide and methane. The latter two gases get eructated (burped) out the cow’s mouth. The VFAs get absorbed into the bloodstream or carried along into the omasum and abomasum for further digestion.

VFAs are produced from the digestion of starch 17 , lipids 18  and fibre 19 into simple sugars 20 , which in turn get converted to VFAs.

The main VFA compounds are

  • propionate 21
  • butyrate 22 23
  • acetate 24

The VFAs are made available by the microbes to the cow as an energy source. The amount of energy made available to the cow does though depend on the energy content of what the cow is eating.

Cows don’t just eat grass

Leaving aside the contentious issue of modern cattle feed (stuff like soya, other grains and even chicken manure), the natural forage that cows eat, in addition to a wide variety of natural grasses, include legumes like alfalfa, trefoil, milkvetch, clover, sanfoin and others. which provide a better source of protein than grass alone and are often included in the range of pastures and hay. Grain, by the way isn’t as good a protein source since it’s more starch than protein.

Protein, starch & fibre

If the forage has a high energy content, then the microbes get lots of energy and there’ll be some left over for the cow herself. However, if there’s low energy (starch) and high fibre, there’s less remaining energy available even if the cellulose-digesting bacteria can derive plenty of energy for themselves from the cellulose. Cellulose is more fibre than energy, compared with starchy sources. This means that if a cow eats too much fibrous forage with insufficient starch, she could actually starve to death.

Protein sources

Cows get their protein is from two main sources: digesting the microbes themselves (as microbial protein), and from the plant sources (as by-pass protein).

Surprisingly enough, microbes (dead or still alive) provide the cow with 40% of her protein sources. The microbes only live for around 15 minutes, so as the plant material from the rumen moves through the rest of the digestive tract, most microbes that go along for the ride are dead, with some still clinging on to life before being digested and used as a protein source.

The plant protein that the microbes don’t digest themselves (and, of course, microbes need protein too), will pass through to the omasum and onwards, or get absorbed into the bloodstream. Too much protein and it will passed out in urine and faeces; too little and she could become deficient. Protein deficiency will tend to cause the cow to search for other sources of food which are perceived as protein, such as salt and phosphorus.

Fat isn’t a problem for cows

Fat requirements are not as important to cows as are requirements for energy and protein. This is because they already have a source of fatty acids derived from the microbial digestive process occurring in the rumen.

Salt can be a problem

Salt can often be deficient in a cow’s diet. Grass doesn’t give all the nutrients to a cow. A vegetarian diet is low in sodium when compared with an omnivore’s or carnivore’s diet. Salt (sodium chloride) is essential for their bodily requirements (osmosis 25 and other cellular functions).

Soil deficiencies

Soil can also be deficient in other minerals that the cow requires in small quantities, such as sulphur, selenium, iodine, cobalt, copper, etc. Modern soils can be bleached out through overproduction. Additionally, cows may be forced to live in low-mineral areas where they wouldn’t naturally decide to live if they were left to roam free and decide for themselves where they wanted to live. This means that supplementation with a mineral/trace-mineral salt block is usually necessary to prevent mineral deficiencies.

Plant nutrient value varies

Grasses and forbs 26  don’t maintain the same nutrient level throughout seasons.

A plant’s most nutritious stage is often just before flowering or the emergence of the inflorescence 27 . This is when they are mostly water.

A plant’s least nutritious stage is at emergence and still below a height of 10 inches, and also when they have gone into dormancy. This is when they are mostly fibre.

Cows eat nails and magnets

Well, not strictly true – but they do often swallow metal objects (such as nails or wire) when foraging, and farmers sometimes make cows swallow magnets. But why?

When any ruminant swallows metal, it sinks into the reticulum. There it can move onwards or, while still in the reticulum, penetrate the lining and cause a condition called hardware disease 28 .

Farmers often ‘feed’ a magnet to their cow because it helps to hold any metal bits safely together in one place, reducing the risk of the above condition.

As with everything else, there’s competition for providing farmers with the best cow magnets – and websites devoted to offering them an interesting range of magnetic options! 29

Final thought

So, an unusual blog subject for this WFPB site, but I hope it was of some interest. It’s fascinating how nature creates digestive systems so perfectly suited to the food source. As I hinted at above, the issue of whether our digestive system is best designed for plant- or meat-eating is still hotly debated. In the next blog, I want to chew over this particular issue in more detail – leaving Daisy to her cud…



  1. Wikipedia: Ruminant definition []
  2. Wikipedia: Rumen definition []
  3. Wikipedia: Reticulum definition []
  4. Wikipedia: Omasum definition []
  5. Wikipedia: Abomasum definition []
  6. Wikipedia: Cud definition []
  7. Wikipedia: Bacteria definition []
  8. Wikipedia: Protozoa definition []
  9. Wikipedia: Methanogens definition []
  10. Wikipedia: Fungi definition []
  11. Wikipedia: Microbe definition []
  12. Wikipedia: Anaerobic definition []
  13. Wikipedia: Enzyme definition []
  14. Wikipedia: Cellulose/Hemicelllulose definition []
  15. Wikipedia: Cellulase definition []
  16. Wikipedia: VFA definition []
  17. Wikipedia: Starch definition []
  18. Wikipedia: Lipids definition []
  19. Wikipedia: Dietary fibre definition []
  20. Wikipedia: Simple sugars definition []
  21. Wikipedia: Priopionate definition []
  22. Wikipedia: Butyrate definition []
  23. Butyrate – Why Dietary Fibre is So Important []
  24. Wikipedia: Acetate definition []
  25. Wikipedia: Osmosis definition []
  26. Wikipedia: Forb definition []
  27. Wikipedia: Inflorescence definition []
  28. Wikipedia: Hardware disease definition []
  29. Cow Magnet Choices []

Butyrate – Why Dietary Fibre is So Important

The single layer of cells that line our gut has a total surface area larger than a tennis court. If this delicate single-cell layer is compromised, our health very soon deteriorates – with potentially fatal consequences. The unsung hero responsible for protecting our intestinal health is a chemical called butyrate. Let’s take a quick look at just how important this little-known short-chain fatty acid (SCFA) is and why dietary fibre is so vital to its functions.

There are literally trillions of bacteria in our intestines (also called the gut) – some good guys and some very bad guys. What we want to do is ensure that the good guys survive and the bad guys (such as campylobacter or salmonella) don’t.

But our bodies can mistake the good guys for bad guys if there’s not enough fibre in the diet – an increasingly common reality in the modern western diet of highly processed, low-fibre food.

Good bacteria produce butyrate

Good bacteria in the colon feed on fibre and produce butyrate as a by-product. The butyrate in turn “calms down” our immune system, preventing it from regarding the good bacteria as foreign invaders and hence attacking them. However, if there’s insufficient buyrate being produced by the good bacteria – something that happens if they don’t have enough fibre to feed on – the immune system then assumes that the good bacteria are bad guys and attacks them. This can result in inflammation and the potential breakdown of the intestinal wall.

Quid Pro Quo

Research has demonstrated clearly that when we feed the good bacteria in our gut, they feed us right back; but stop feeding them and the health of our gut will deteriorate rapidly.

There’s an obvious evolutionary advantage for the good bacteria to want to keep us alive and healthy: if we die, they die.

This isn’t the case for the bad bacteria (such as cholera) which cause diarrhoea. The result of this is that they spread out of our bodies and can infect other people. It makes no difference to the bad guys whether we live or die – so long as we produce enough diarrhoea to spread them about the environment before we die.

A Fine Balance

Our immune systems have to maintain a fine balance between tolerating the good bacteria while attacking the bad. If this balance is disturbed by a lack of dietary fibre, it may lead to inflammatory bowel disease. Researchers found that butyrate “may behave as a microbial signal to inform [our] immune system that the relative levels of [good] bacteria are within the desired range.” If the butyrate levels are low, our immune system starts to attack all the gut bacteria.

Evolution vs Low-Fibre Diets

Butyrate has been involved in suppressing our immune systems for a very long time and for a very good reason. There are times when our guts are invaded by large amounts of bad bacteria. When this happens, we don’t want our immune system to go to sleep on the job – we want it to attack them and get rid of them. Once it’s done its job, and the bad guys are gone, the good bacteria will start producing butyrate and this will put the immune system back on “stand by”.

But this will only happen if we eat enough fibre; otherwise, our immune system stays on “red alert” with the resulting bad news for our intestinal health.

Fibre From Food Not supplements

Whilst research shows that fibre intake is “critical for optimal health”, there’s no magic pill that will replace the role played by the fibre in whole plant food. True, you come across bold claims for the effectiveness of fibre supplements such as Metamucil and psyllium, but the above research suggests that these supplements do “not replicate the results seen with a diet naturally high in fib[re].” This opinion is supported by Dr Greger.

The Many Health Benefits of Butyrate

Researchers concluded that “[t]he effects exerted by butyrate are multiple and involve several distinct mechanisms of action.” as the main end product of the microbial fermentation of dietary fibres in the human intestine, butyrate plays a vital role by:

  • maintaining intestinal homeostasis and overall health status
  • regulating gene expression
  • controlling the fate of cells through the inhibition of histone deacetylases (HDACs)

At the intestinal level, butyrate:

  • prevents and inhibits colonic carcinogenesis
  • protects against inflammation
  • reduces oxidative stress
  • provides a defence barrier for the epithelial cell layer
  • modulates visceral sensitivity
  • facilitates intestinal motility

At the extraintestinal level, butyrate offers potential for the treatment of:

  • sickle cell disease
  • β-thalassemia
  • cystic fibrosis
  • urea cycle enzyme deficiency
  •  X-linked adrenoleukodystrophy
  • hypercholesterolemia
  • obesity
  • insulin resistance
  • ischaemic stroke

Fork vs Pill

A growing number of studies (see References below for a wide variety of related research papers) have revealed new mechanisms and effects of butyrate. The majority of research projects are, of course, working within the paradigm that requires reductionist methods to produce patentable outcomes (largely pharmaceutical in nature). And whilst the evidence suggests that the fork is more effective than the pill in treating chronic non-communicable diseases (diabetes, hypertension, cancer, heart disease etc), the very fact that the scientific community is so positive about the wide range of benefits of butyrate – from the intestinal tract to peripheral tissues – reminds me of how wonderful the body is at healing itself. However, in order to ensure we benefit from the full protection of butyrate, we need to eat a WFPB diet packed full of fibre.


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