Even though thousands of research studies have already been carried out, the human microbiome is still an almost unexplored land.

It’s instinctive to think that our bodies are fully independent; a perfect machine built with all that is necessary to live.

Our organs execute all the crucial functions that we need – they enable us to breathe, assimilate food, pump blood into the veins… However, there is something in our body that is not “part of us”, but which turns out to be incredibly important to the ways in which our bodies function: the unimaginable number of micro-organisms that reside on our skin, in our mouth, in our gut and in other parts of our body.

This rich and diverse microbial community – the human microbiome – has evolved alongside humans in a constant, mutual relationship: microbes are with us from the moment we are born until the moment we die, developing with us through all stages of life. 

Scientists are now revealing just how important this population of microbes is for our overall health and well-being, and suggesting ways in which we can take care of it.

1. Trillions of microbes live with us

Scientists have classified more than 10,000 different species of micro-organisms populating our body, amongst which they’ve estimated there is up to 100 trillion single micro-organisms. Some recent studies have estimated that number at a lower approximation of around 30 trillion, but it is undoubtedly still a huge population – particularly when compared to the number of human cells in the body, which is “just” 10 trillion. 

Even from a genetic point of view the dimension of the microbiome is impressive, with approximately 3.3 million genes in the microbiome compared to the approximately 22,000 in the human genome.

Bacteria, archaea, fungi, protists and viruses are all different kinds of microbes that compose the wonderful community of our microbiome. They inhabit the different parts of the body – the mouth, the skin, the vagina, the uterus, and so on – spawning different sub-communities of the human microbiome. But definitely the largest community and probably the most important, is the gut microbiome.

2. Our gut microbiome is just like another organ

Our microbiome – especially the bacteria populating the gut – takes care of many tasks relevant to our well-being. For example, through fermentation, bacteria digest fibres that our small gut cannot break down, and synthesise vitamins.

As Dr. Daniela Weiler, oncologist at the Lucerne Hospital and specialist of nutritional medicine, states in a Curaden Academy webinar on the microbiome and nutrition, “gut bacteria can manufacture about 95% of the body’s supply of serotonin,” which regulates our mood. The microbiome also communicates with our immune system, has an impact on metabolism and – when not well balanced – can influence the development of diseases.

As early as the start of the 1990s, scientists started to refer to the gut microbiota as a virtual or forgotten organ. And “like any other organ,” as explained by microbiologist Fernando Baquero, “the microbiome has physiology and pathology, and its individual health might be damaged when its collective population structure is altered.”

However, unlike other organs, we still don’t know a lot about it. In fact, even though thousands of research studies have already been carried out, the human microbiome is still an almost unexplored land.

3. Diet, drugs and sport shape our microbiome

Each gut microbiome has a fairly unique character, with 80% of its composition varying from person to person. Still, do we have any ability to influence which microbes are living in our intestines? Luckily, yes – to a certain extent – through nutrition. 

Experiments have shown that changing our diet can induce large, temporary shifts in our microbiota within 24 hours. More stable alterations happen in one week. Researchers from the University of California comprehensively described, in a paper published in the Journal of Translational Medicine, how diets rich in plant proteins and fibres are linked to a more diverse and balanced microbiota, which definitely helps our health. Conversely, a diet high in animal protein and fat lowers the number of total bacteria and their diversity, leaving space for opportunistic microbes that lead to a higher risk of developing inflammation, to settle. 

In the Curaden Academy webinar on the microbiome and nutrition, Dr. Daniela Weiler warns that the diversity of the gut microbiome is also negatively affected by drugs like antibiotics, antidepressants and laxatives, whereas physical activity and good oral health both have a positive impact.

4. Good microbes fortify our immune system and help our digestion

Most of the bacteria populating our gut represent a beneficial relationship to our body. Bifidobacterium and Lactobacillus are some of these good bacteria (see an overview of the gut’s bacterial genera and species here). Digesting fibres that our small gut normally cannot break down, they manufacture particularly helpful byproducts for us: the short chain fatty acids. 

As described by scientists at the Imperial College of London, “the short chain fatty acids produced primarily from the microbial fermentation of dietary fibre appear to be key mediators of the beneficial effects elicited by the gut microbiome.”

Acetate, propionate and butyrate, for example, are short chain fatty acids that trigger a stabilising effect on our immune system, lowering the inflammatory responses and promoting tolerance and homeostasis. Essentially, they balance the whole system. The short chain fatty acidsare also known for regulating food intake, helping us to control weight.

5. Up to 90% of all diseases are somehow influenced by the microbiome

If a balanced microbiome is our ally in staying healthy, a poorly balanced and less diverse microbiome is something we want to avoid: it increases the risk of inflammation and leaves space for other – less beneficial – pathogenic microbes to settle. In fact, as Dr. Daniela Weiler suggests in her webinar, up to 90% of all diseases appear to be indirectly or directly linked to the microbiome.

She describes how research studies have shown this connection. For example, an ill-composed gut microbiome is linked to a higher risk of “incorrect”, inflammatory responses in our immune system, which are the cause of autoimmune diseases. Chronic inflammation appears to also increase the risk of cancer, while other gut microbes have a more direct connection to cancer. 

Obesity may also be linked to our microbes. It has been scientifically observed that obese and lean people have very different compositions of the gut microbiome. Researchers also found associations with cardiovascular diseases, diabetes, Alzheimer’s disease, autism and psychiatric disorders such as depression. 

Other human communities of microbes – like the mouth microbiome – are also somehow linked to diseases. For example, scientists have detected the same bacteria associated with gum disease in both colon and pancreatic cancers.

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Sources: 

• Curaden Academy webinar, Microbiota and nutrition: Difference between health and disease by Daniela Weiler
• What’s the difference between microbiome and microbiota
• That gut feeling by Dr. Siri Carpenter
• Influence of diet on gut microbiome
• Who would have guessed that sport is impacting our gut microbiota?