Gut disorders are on the rise, with half of Australians complaining of some digestive problem in any 12-month period, according to The Gut Foundation of Australia.
Multiple factors are responsible for this increase, but there is a growing body of research indicating that the community of microorganisms living in our gut, called the gut microbiome, could be playing an important role.
There has been an explosion of research over the last 10 years showing that people with different disease states have different populations of bacteria in their gut, compared to healthy people. These include such wide-ranging diseases as inflammatory bowel diseases, colon cancer, cardiovascular disease, diabetes, Parkinson’s, asthma, and even depression. This research opens the exciting possibility that in the future we may be able to diagnose or even treat some diseases through modulating the gut microbiome.
It is important to remember, however, that right now we only know that some species or functions of the gut microbiome are correlated with disease; we do not know if changes to the gut microbiome cause disease, or if the disease causes the gut microbiome to change. Ongoing research is working to tease apart these relationships so that in the future, it may be possible to develop diagnostics and treatments using this knowledge of the gut microbiome.
One way scientists are progressing this exciting area of research is through gut microbiome testing using advanced sequencing technology called metagenomics. This technology identifies both the microbial species and the genes within each species. The genes provide a blueprint for what a microorganism can do, such as producing metabolites that influence health or disease. By understanding which genes a microorganism has, we can gain greater insight into the role that microorganism may play.
Below are a few examples of microbial metabolites that researchers are actively studying for the role they may play in our health:
Short chain fatty acids
When gut bacteria break down fibre, they primarily produce short chain fatty acids such as acetate, propionate and butyrate. Scientists are discovering that these short chain fatty acids are incredibly important for our health because they are involved in several bodily functions such as helping to: maintain glucose stability, regulate appetite, provide fuel for intestinal cells, maintain the intestinal cell barrier, regulate the immune system, and reduce inflammation. It is likely that as our understanding of the various inflammatory mechanisms involved in disease advances, short chain fatty acids will be playing an important role.
3-indolepropionic acid (IPA) is a strong anti-oxidant produced by some gut bacteria that can help protect the nervous system from damage. Research has shown low levels of IPA may play a role in the development of type 2 diabetes and research in animal models suggests that IPA may also play a role in maintaining the gut barrier. IPA is formed by breaking down the amino acid tryptophan. One study observed that consuming foods high in dietary fibre, and in particular rye, correlated with increased IPA production.
GABA is short for gamma-butyric acid and is an important signalling molecule for the brain (called a neurotransmitter). GABA plays a key role in reducing the activity of nerve cells, and low levels of GABA have been associated with anxiety and depression. Although GABA is primarily produced by your body, some gut bacterial species can also produce (and consume) GABA. A couple of studies using animal models have demonstrated that administering a bacterial species that can produce GABA resulted in changes to GABA receptors in the brain and the activity of sensory neurons. This suggests it is possible for excess GABA produced by gut bacteria to be taken up by mammalian nerve cells, at least in animal models. It is still too early to know if the same applies in humans, but it offers a tantalising possibility for future research.
Lipopolysaccharides (LPS) are an important component of the cell wall of many bacteria, but when these bacteria die, the LPS is released into the gut where it can promote inflammation. A high potential to produce LPS has been observed in individuals with colon cancer, Crohn's disease and insulin resistance. Additionally, high blood levels of LPS have been observed in individuals with metabolic conditions such as heart disease, type 2 diabetes, non-alcoholic fatty liver disease and obesity. Research suggests that high-fat diets can allow increased quantities of LPS to diffuse from the gut into the blood circulation. Reducing the intake of fat can help reduce the ability of LPS to enter the bloodstream.
It is an exciting time in medicine as researchers are uncovering more about the how the gut microbiome may influence our health and it is likely that metabolites, such as the ones listed above, will be playing an important role. Tools such as metagenomic sequencing present a valuable opportunity for both researchers and consumers alike to gain a deeper insight into the gut microbiome and how metabolites such as these may be linked to health. In the next decade, it is entirely possible that an annual check-up at your GP will involve not only a blood test, but also a screen of your gut microbiome.
Alena Pribyl is a senior scientist at Microba.