What is the gut microbiota?
Inside our digestive system, tens of trillions of microorganisms and at least 1000 different species of bacteria have made a comfortable home for themselves. This incredible collection of microorganisms – such as bacteria, viruses, and yeast in our digestive system – is known as our gut microbiota.
Research into the area of our microbiome is showing us our knowledge is still in it’s early stage, while the two most dominant bacteria in the gut are Firmicutes and Bacteroides (representing some 70-75%) there is an increasing diversity of what is termed 'phyla' being uncovered.
So, what is the gut microbiome then?
The terms microbiome and microbiota are often used interchangeably, but they have different meanings. The gut microbiome is the name for the genes inside the cells of all the microorganisms in our gut combined. No two gut microbiomes are the same – but, there are certain combinations of microorganisms in our gut microbiota that are common in most people.
What does our gut microbiota do?
While many of us associate bacteria and viruses with illness, the microorganisms in our gut microbiota aren’t invaders – they’re actually extremely valuable colonisers. Here’s why - The microorganisms help us to digest foods that we’re otherwise unable to digest. They do this by turning all those non-digestible carbohydrates – such as resistant starches, cellulose, pectins, and gums – into energy and absorbable nutrients.
These nutrients benefit us – but impressively, they’re also used by the bacteria themselves to grow and flourish. Speaking of nutrients, our gut microbiota produces valuable vitamins – such as vitamin B12, thiamine, riboflavin and vitamin K, which is essential for the clotting of our blood.
And if that’s not enough, our microbiota also protects us from other bacteria that can cause disease. It does this by producing what’s known as bacteriocins, which are antimicrobial substances that stop pathogenic bacteria from growing in our gut. There’s a growing body of evidence suggesting that, in addition to supporting gut health, the microbiome may be important for other areas of health, such as immunity. Specifically, the microorganisms in our microbiota may be able to support the development and function of immunity by ‘training’ the immune system to tolerate non-harmful microorganisms and react to harmful pathogens.
How does our gut microbiome develop?
Remarkably, our gut microbiome starts to develop as soon as we’re born. Even in the first hours after birth, babies are picking up useful microorganisms from their environment. As we come into contact with new people and foods, the microflora mix in our gut continues to grow and adapt to the available nutrients in our diet. A baby’s gut microbiota, for example, has microorganisms that help digest the sugars (oligosaccharides) in milk. When babies begin to eat solid foods, their gut microflora will also start to contain microorganisms involved in digesting sugars (polysaccharides) in solid foods. When we’re about one year old, our gut microflora is already much more diverse than when we were born. It continues to develop as we eat more solid foods and explore the world around us.
Around age three, the composition (the specific microorganisms) and diversity (the different kinds of microorganisms) of the gut microbiota is similar to that of adults and stays relatively stable throughout adult life. However, as we move into old age, we begin to lose some of this stability and the composition of our gut microflora changes again. This change doesn’t necessarily affect our health – though some researchers suspect that, in some cases, it could contribute to health issues in our gut.
What does a healthy microbiome look like?
So, what exactly is a ‘healthy’ gut microbiome? It’s a question more and more researchers around the world are investigating as they strive to understand how an unhealthy gut microbiome may cause – or be linked to – disease and poor health. Identifying the characteristics of a healthy microbiome is a challenging task, though – especially as each of us seems to have a unique microbiota that is constantly evolving. Still, researchers have proposed that a healthy microbiome has the following three characteristics:
What can change our gut microbiome?
One significant factor that can affect the microbial mix in our gut is antibiotic use. Antibiotics don’t just kill pathogenic bacteria – they kill all bacteria in their path. This means that, when we take antibiotics, the beneficial bacteria in our gut will suffer, too. While these changes in our gut microflora are usually only temporary, not everyone’s gut microbiome recovers immediately. Some people may take a few weeks, or even a whole year, to recover fully.
Another huge factor affecting the microflora in the gut is our diet – specifically, our long-term dietary habits. Long-term, established habits may actually change the type of microorganisms in our gut. In one study, researchers found that a diet high in carbohydrates was linked with a high amount of Prevotella bacteria in the gut microbiome. On the other hand, diets high in protein, especially meat, were associated with a gut microbiome rich in Bacteroides bacteria.
Whether these changes in our gut are healthy or may cause disease is another million-dollar question that researchers are now investigating. It's also not yet clear how a high carbohydrate or protein diet actually changes the microbial mix in our gut.
Researchers are learning more about specific behaviours, though. Prevotella bacteria, for example, can use carbohydrates to grow which might give these bacteria a head start when compared with other bacteria that can’t use carbohydrates to grow. This head start might also mean Prevotella bacteria also outgrow others. So, while scientists are constantly learning more about how eating can change the microorganisms, they’re still investigating whether these changes actually help or hinder our health.
Short-term changes in our diet can affect our gut microbiota, too. In one small study, people who changed their diet to meat, egg and milk drastically changed their gut microflora. Within just five days, these peoples’ gut contained more bile-tolerant bacteria and fewer bacteria that metabolise plant polysaccharides. Unfortunately, researchers don’t yet know exactly how specific aspects of our diet interact with our microbiome. Still, the emerging research suggests that we may one day know how to modify our diets to ensure a healthy microbiome and ultimately maintain or improve our health.
Words by Leanne Cooper, Registered Nutritionist, Educator and Founder and Director of Well College Global
Want to learn more about the GUT and how it affects our health? Click the link below to enrol to the Well College's online course - Trust your GUT: Gut Health and the Microbiome
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