Improve your gut - improve your immunity!

Improve your gut - improve your immunity!

We each carry 40 trillion microbes and in our last blog (read here), we wrote about the important role these microbes play in “gut-mediated immunity.” We introduced “commensal bacteria” – the good guys that support our health and wellbeing and in this blog, we are going to discuss how you can support the gut bacteria ecosystem for better health.

What’s in our gut?

The gut is actually one long tube which begins with our mouth and ends in our rear, twisting and turning along the way (see below). The gut environment changes in terms of gases and acidity and as such, the bacterial species change.

The human digestive system - or "gut"

Amazingly, the colon contains the highest microbial density recorded in any habitat on earth, representing between 300 and 1000 different species. Even though there is large diversity, 99% of gut bacteria come from 30-40 species.

Like a fingerprint, each person's microbiota is unique: it’s determined partly by our mother’s microbiota and partly from our diet and lifestyle. The dominant genera of bacterial species colonised in human guts include:

Bacteroides, Clostridium, Fusobacterium, Eubacterium, Ruminococcus, Peptococcus, Peptostreptococcus and Bifidobacterium.

Other genera, like Escherichia and Lactobacillus, are also present, but to a lesser degree.

Examining the species in our gut is a clue to the types of food we eat (read more here). For example:

  • The Bacteroides genus is highly associated with the consumption of animal proteins, amino acids and saturated fats, which are typical components of Western diet;
  • The Prevotella genus is associated with the consumption of carbohydrates and simple sugars, which are typical of societies who cultivate grains.

The dominant genus can shift over time with changes to diet and subtle changes also happen on a daily basis according to our stress levels, hormone levels and whether we exercise.

In a study which assessed Asians who had moved to the United States, it was found that after the move, individuals had reduced gut microbial diversity and function (read more here). What also happened was bacterial strains from the genus Prevotella, whose enzymes degrade plant fibre, became displaced by dominant strains from the genus Bacteroides and this was correlated with the amount of time the individual had spent in the United States.

What does good look like?

For good health, we want to promote the presence of bacteria that ferment dietary fibre and produce short-chain fatty acids. These short chain fatty acids are internal signals in our body and play roles in lipid balance and reducing inflammation (read more here).

The role of prebiotics

Both probiotics and prebiotics are important in gut health, but varied prebiotics are critical in improving our microbiota as they create the environment for the good bacteria to thrive.

Prebiotics are the fibres present in fruit and vegetables. Humans cannot digest prebiotic fibres, but certain beneficial microbes in our gut can (read more here). Not all fibres can be classified as prebiotic (as some can’t be broken down, even by our gut bacteria); however, most prebiotics can be classified as dietary fibres.

Fibres and prebiotics are diverse in chemical composition and can be grouped by their solubility; viscosity and fermentability, which all affect how they are processed in the body.

Plants will generally have a mixture of fibre types and some plants will be rich in a particular type (the table below shows examples).

For example, bananas contain resistant starch and inulin-type fructans, while kiwifruit, citrus and apples are sources of pectin - all of which are fermented and broken down by different bacteria in our colon.

Few gut bacteria possess all of the enzymes required to break down the fibres, so often many different bacteria are required to fully utilise a prebiotic fibre.

With a prebiotic fibre of sufficient complexity, an entire ecosystem of bacteria is required, forming chains of successive bacteria all breaking down the prebiotic fibre and benefiting from the action (and metabolites) of the bacteria before them.

All of this is further modified by the solubility and viscosity of the prebiotic fibre. For example, pectin is one of the most structurally diverse and complex polysaccharides found in nature, yet it is fully fermentable by a consortia of bacteria, in part because it is soluble.

In contrast, cellulose, comprises one single sugar type and one linkage, is insoluble and forms crystalline lattices which resist bacterial enzyme action, making them almost fully non-fermentable - but still important for our health and promoting regular bowel movements.

Eating a full array of prebiotic fibres, with their different fermentability, solubility, and viscosity characteristics is what creates a diverse microbiota and improvements in our health.

Examples of prebiotic fibre types and categories in which they fall - some plants will have prebiotic fibres that fall into multiple categories.

Fibre types


Digestive impact

Plant species (good source)

Bulking fibres

Cellulose, hemicellulose, psyllium

Absorb and hold water promoting stool regularity

Cereals, plantago

Viscous fibres

Beta-glucan, psyllium

Thicken faecal mass

Oats, plantago

Fermentable fibres

Resistant starch, pectin, inulin, oligofructose

Feed microbiota of large intestine, metabolised to yield short chain fatty acids

Beans, lentils, green bananas, citrus fruits, root vegetables

Soluble fibre

Beta-glucans, psyllium, inulin, wheat dextrin, oligosaccharides

Fermented in colon into bioactive products such as short chain fatty acids, delays gastric emptying (extends feeling of fullness)

Oats, barley, legumes, bananas,

There is a lot to unpack here, but given we have already explored the crucial role of gut health in good immunity – the most important message is:

Eat lots of different plants - fruit, vegetables, seeds, grains, legumes and nuts - aim for 30 different plant species a week. This will ensure you slowly shift towards having a more diverse gut microbiota with species which are able to break down prebiotic fibres and produce the wonderful short fatty acid signals our immune system depends on.

Please contact us if you have any queries and don’t forget to check out our new Zestt Wellness lozenge range and Breathe Easy!

Back to blog