The Human Gut Microbiome
The human microbiome refers to the symbiotic relationship between microorganisms and their collective genes. The gut microbiota is the total collection of bacteria, archaea, and eukarya occupying the gastrointestinal (GI) tract. Over many years, it has co-evolved with the host to form a complex, mutually beneficial relationship.
The number of microorganisms in the GI tract has been estimated to be more than 10^14 with approximately ~10 times more bacteria than human cells. However, according to a recently updated estimate, the ratio of bacteria to human cells is potentially closer to 1:1.
Development and Composition
The development of the microbiota was believed to begin at birth, although new evidence has suggested babies come into contact with microbes while still in the womb. As you grow, the gut microbiome begins to diversify, which means it contains a diverse range of microbial species. A higher microbiome diversity is considered to be good for your health. A large-scale study has calculated that the human gut microflora is made up of over 35,000 bacterial species, each of them playing a different role in your body. Most of these are important for your health, whilst others may cause diseases.
Factors that affect the composition and function of the gut microbiome include diet, genetics, use of medications such as antibiotics, mode of delivery at birth, etc. Dysbiosis refers to the compositional and functional alterations of the microbiome, which often lead to health problems.
Dysbiosis is important as changes to the composition of the microbiota is associated with diseases such as obesity and diabetes. This is shown by the characteristics of diabetes and obesity, which includes an altered gut microbiota, inflammation, and a gut barrier disruption. Although diabetes is influenced by both hereditary and environmental factors, studies suggest there may be a gut microbiota signature that promotes intestinal inflammation and subsequent systemic low-grade inflammation. Both of which encourage the development of type 2 diabetes.
This shows that gut microbiota in humans can evolve throughout life and play a significant role in both health and diseases.
Importance of the gut microbiome
The human gut microbiome is so important because it has such a powerful impact on the body.
For example, it can affect heart health. A study with a sample of 1,500 participants found that the gut microbiome plays a role in promoting ‘good’ HDL cholesterol and triglycerides. However, particular unhealthy species such as Emergencia timonensis in the gut may contribute to heart disease by producing trimethylamine N-oxide (TMAO). This is a chemical that contributes to blocked arteries, therefore increasing the possibility of having a heart attack or a stroke. Specific bacteria within the microbiome can convert choline and L-carnitine, which are both nutrients found in red meat and other animal-based food sources, to TMAO, increasing the risk factors for heart disease.
Furthermore, the gut microbiome helps maintain overall health by influencing digestion, immunity, and even brain function through the gut-brain axis. The intestinal microbiota and its metabolites have likely found a pathway to the brain through the gut-brain axis, which is a bidirectional communication system that combines immunological, hormonal, and neurological signals between the gut and the brain. This allows the brain to regulate immunological and gastrointestinal processes, including peristalsis, mucin production, and immune functions. Key findings demonstrated stress affects the gut microbiota’s composition, and the host's stress response is influenced by the gut microbiota’s bidirectional communication with the central nervous system. Stress affects the integrity of the gut epithelium and alters peristalsis secretion and mucin production. This modifies the intestinal microbiota’s habitat and encourages changes to the microbial composition and/or metabolism, resulting in dysbiosis.
Moreover, the gut microbiome has an important role in host protection and the development of the immune system. The mechanism known as the barrier or competitive-exclusion effect refers to the intestinal bacteria producing antimicrobial compounds, competing for nutrients, and sites of attachment in the gut lining, which prevents colonisation by pathogens. In the gut wall, host cells have attachment sites that are used by pathogenic bacteria to enter epithelial cells. Non-pathogenic bacteria in laboratory studies have been seen to compete for these attachment sites in the border of intestinal epithelial cells, preventing the attachment and entry of pathogenic, enteroinvasive bacteria.
In addition, bacteria-producing antimicrobial substances known as bacteriocins can inhibit the growth of their competitors, and this ability is widely distributed among gastrointestinal bacteria. Also, bacteria compete for nutrients in their surroundings and maintain their collective habitat by using and consuming all resources. This means that the enteric microbiota can outcompete pathogenic bacteria for resources because they are more abundant.
How to improve your gut microbiome:
There are many ways to improve and reset your gut health. Here are a few examples:
- Eating a varied and wide range of foods results in a diverse microbiome, a sign of good gut health. Specifically consuming legumes, beans, and fruits, as these contain lots of fibre and encourage the growth of healthy Bifidobacteria. In addition, fermented foods such as yoghurt, sauerkraut, and kefir contain mainly Lactobacilli, which are healthy bacteria and can reduce the amount of disease-causing species in the gut.
- Limiting the intake of artificial sweeteners can also improve your gut microbiome. Evidence has demonstrated artificial sweeteners such as aspartame increase blood sugar by stimulating the growth of unhealthy bacteria in the gut like Enterobacteriaceae.
- Furthermore, staying hydrated is crucial for your gut health. Drinking lots of water may be linked to increased diversity of bacteria in the gut, though the source of the water is taken into consideration. A study conducted in 2022 by Vanhaecke and his peers concluded that individuals who drank more water had lower levels of a particular type of bacteria that can cause gastrointestinal infections.
Written by Suheyla
Moderated by Adelene
References:
Thursby, E. and Juge, N. (2017) Introduction to the human gut microbiota, The Biochemical journal. [online] Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC5433529/ .
Robertson, R. (2023) How does your gut microbiome impact your overall health?, Healthline. [online] Available at: https://www.healthline.com/nutrition/gut-microbiome-and-health#TOC_TITLE_HDR_7
Wen, L. and Duffy, A. (2017) Factors influencing the gut microbiota, inflammation, and type 2 diabetes, The Journal of nutrition. [online] Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC5483960/
Bull, M.J. and Plummer, N.T. (2014a) Part 1: The human gut microbiome in health and disease, Integrative medicine (Encinitas, Calif.). [online] Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC4566439/#b19-17-22
Vanhaecke, T. et al. (2022) Drinking water source and intake are associated with distinct gut microbiota signatures in US and UK populations, The Journal of nutrition. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC8754568/#:~:text=Conclusions,future%20microbiome%20analyses%20is%20warranted
