There is rarely a day that goes by that I don’t read about or discuss gut microbiome/microbiota or gut flora, and it has been receiving increased attention over the last decade. But what do all these terms actually mean?
The microbiota is the community of trillions of bacteria, fungi and other microorganisms that colonise our bodies, and the microbiome is the collection of them in a particular environment, in this case the gut. People often use the word flora instead and this is interchangeable with microbiota.
So now we know what the terms mean, next is, what do they do?
We often think of organisms and bacteria as something negative or bad, that we need to see the doctor about, but the majority of microorganisms are harmless, and in the case of the gut, often beneficial. We have a symbiotic relationship with most gut microbiota – they live happily in our bodies, feeding off us, and in exchange they produce by-products which are needed for many of our functions. The following outlines the different parts of our body that the gut microbiome affects:
Unsurprisingly the gut microbiota have benefits to your gut directly. They aid in the fermentation and breakdown of foods that would be otherwise considered non-digestible, like dietary fibre and the intestinal mucus that our bodies produce, and in doing so they are able to salvage and increase the extraction of energy and nutrients from these foods. The fermentation of dietary fibre also has a stool bulking effect, aiding in the passage of healthy stool. Furthermore, the fermentation process reduces the pH in the gut, reducing the risk of pathogens (the bad sort of bacteria and organisms) and the production of antimicrobial substances. It’s not only about how the presence of the bacteria helps our guts, but also about what the absence of the bacteria could mean. There have been a number of studies to show that when we take antibiotics, and therefore disrupt our natural gut microbiota, there is increased development of gut inflammation. It is likely related to the role the microbiota has in the development of the intestinal mucosa (the lining of the intestine).
The mechanisms by which gut microbiota disturb the metabolism are not well understood, however, as explained above, the gut microbiota is influential in the absorption of food, and in inflammation, which are both processes integral in the development of obesity and diabetes.
We also know that the gut flora has been found to have an effect on the signals that govern our appetite, and as such, the poor health of the microbiota has been linked to obesity. Studies have reported that the production of the chemical acetate by altered gut microbiota activates the part of our central nervous system responsible for the secretion of the hormone ghrelin. This hormone is also known as the ‘hunger hormone’ as it stimulates appetite.
Gut bacteria can also affect our appetite through the process of producing the chemical serotonin. This neurotransmitter is often dubbed the ‘happiness hormone’, as it is considered a contributor to well-being, and we know that many who suffer with depression produce low amounts of serotonin. But this chemical is also involved in the regulation of energy balance, which may partly be why one of the symptoms of depression can be low energy and fatigue. An estimated 90% of serotonin is thought to be produced in our gut and it is the gut bacteria that helps our gut to produce this.
Type 2 Diabetes
The development of Type 2 diabetes is very much linked to obesity, and they share in how disturbance of the gut microbiome may attribute to them both. Research has shown how the microbiome not only contributes to the regulation of energy metabolism as described above, but also to the balance of glucose (sugar) and lipid (fats). Trials have shown that when the gut microbiome is functioning optimally and producing higher amounts of short chain fatty acids (a metabolite of carbohydrate) it correlates with reduced insulin resistance. Insulin resistance occurs when the cells in the body do not respond properly to the hormone insulin, which is a factor that leads to Type 2 diabetes. In addition, a deficiency of these fatty acids is associated with the development of Type 2 diabetes. Furthermore, it has been found in mice, that pulsed antibiotic treatment which will affect the gut microbiome, increases the incidence of diabetes in susceptible mice.
Not only does the gastrointestinal tract harbour a vast microbiome, but it also contains a large pool of immune cells. The gut microbiome has been found to communicate with these immune cells, thus controlling how your immune system works and responds to infection. In the same way that antibiotics affect the health of our gut, studies have also shown that antibiotics can alter the cells that regulate immune responses. In mice studies, antibiotic treated mice have a lower number of T-cells than in untreated mice. T-cells are part of our white cells, which are an essential component in our immune system.
Increasing number of studies are supporting the communication of the gut microbiome to the central nervous system in what is termed the ‘gut-brain axis’. Stress has been found to increase the permeability or ‘leakiness’ of the intestines, which allows bacteria to travel across the intestines and access the nervous system. We have already discussed how 90% of the body’s serotonin is produced by the microbiome in the gut and how this may affect depression, but further studies have shown us how behaviour may be affected when our gut microbiota is disturbed. Increasing inflammation in the gut correlates to increased anxiety and depression symptoms, and on treating with probiotics, there has been shown to be improvements in these symptoms.
There is increasing evidence to support the role of the microbiome in cancer therapy. We have discussed how the microbiome can affect the immune system, and it is thought therefore that this is one of the ways it might suppress cancer formation and progression. This has been known for some time, and over 10 years ago the National Cancer Institute showed that by giving antibiotics to mice with melanomas (skin cancer), anti-tumour activity was reduced. It was proposed that the gut bacteria helped to prime an immune response, and this theory has since been supported in a number of studies. It has also been shown that one of the byproducts released from the gut microbes is a fatty acid called butyrate, and that there is evidence to suggest that butyrate can induce the cell death of colon cancer cells.
There are a number of other systems that the gut microbiome has been linked to including the skin, allergies, arthritis and even in Parkinson’s disease, and we continue to learn so much about this ever expanding area. This simply acts as a reminder to treat our gut well, ensuring a well rounded and healthy diet with plenty of pre- and pro- biotics.