The Human Microbiome

What is the Human Microbiome?

The human microbiome is a remarkable ecosystem of largely ‘good’ bacteria and microbes that live on and in the human body. These micro organisms are believed to influence everything from our weight, our immune health, our susceptibility to disease and even our mood.

Our bodies are home to between 40 and 100 trillion microbes according to current estimates– weighing as much as 2 kg (4lb). Most live in our intestine and make up what is know as our gut microbiome.

Many scientists believe we have more of these microbes within us than we have our own cells by as much as 10 to 1. The vast majority of these microbes are considered to be commensal – or friendly and we depend on them for our health just as much as they do us.

Scientists have only recently begun to appreciate the importance of these microbes for our health — possibly one of the most significant discoveries in human biology this century.
Thanks to advances in genetics, supercomputing and AI in recent years Scientists are now able to discover a lot more about these microbes that live in and on us.

Key Facts About the Human Microbiome

  • The human microbiome is made up of between 40-100 trillion micro organisms – which include bacteria, viruses, fungi, protozoa and other organisms
  • Our microbiome contains hundreds of different bacterial species – and over 3 million genes. our gut microbiome has 150 times more genes than the human body does
  • These microbes live on our skin, in our mouths, our lungs and our genitals – however the majority live in our gut – and make up what is known as the gut microbiome.
  • Our microbes live in an ecosystem consisting of hundreds of different strains and species – the make up of which is unique to each of us. we only share about a third of our microbes.
  • The vast majority of these microbes are considered ‘friendly’ and vital to our health, although some pathogens also exist within our microbiome that can infect us and cause disease.
  • Our microbiome is understood to influence everything from our weight, our metabolism, our immunity and even our mental health and behaviour.
  • An unhealthy microbiome made up of the wrong balance of bacteria (known as dysbiosis) is linked with a large number of chronic health conditions and diseases.

Why is the Human Microbiome so Important

The bacteria and microbes that make up our microbiome have existed for millennia in some cases and have evolved with us to the extent that we are now dependent on them to perform a number of roles – from educating our own immune system and fighting infection to the production of enzymes and nutrients critical for our bodies to health and well being.
The make up of the microbiota is unique to each of us – and the right or wrong mix of these microbes is linked with health and diseases such as:

  • Asthma
  • Autism
  • Cancer
  • Celiac disease
  • IBD, Colitis
  • Diabetes
  • Eczema
  • Heart disease
  • Malnutrition
  • Multiple sclerosis
  • Obesity

What does Our Microbiome do?

Our microbiome affects our health through digestion and weight gain, our bodies immunity, our behavior and our risk of disease.

1. Digestion

Our gut microbes help us break down indigestible plant fibre and as well as complex molecules in meat and vegetables that we alone are unable to digest. Our gut bacteria also produce important nutrients that are essential for our health. Gut bacteria help us break down complex molecules in meats and vegetables, for example. Without the aid of gut bacteria, plant cellulose is indigestible.

The make up of our gut microbiota is also believed to determine how much energy we extract from our food and whether we put on weight or maintain a lean body.

The diversity of our microbiota is related to the diversity of our diet. People who consumer a wide variety of different foods re likely to have a more varied gut microbiota than people who follow a predictable diet.

2. Immune Health

Our microbiome helps educate and regulate our bodies immunity and without our microbiota our bodies immune system would be unable to function properly. Scientists have found profoundly ill effects in germ-free rodents – rodents that are sterile of microorganisms – and an underdeveloped immunity is among them.

Our microbiota also linked with auto-immune disorders and allergies. These conditions are thought to be more likely to develop when early microbial exposures are disturbed.

3. Behaviour

Through what is known as the gut brain axis our microbiota can also communicate with and influence our brain. In a recent discovery scientists found that our gut bacteria are able to mimic the molecules released by our nerve endings in our gastrointestinal tract in order to communicate with our brain, influence our mood and even our cravings.

Links have also been observed between the gut microbiome and mental health problems such as depression, anxiety and eve autistic spectrum disorder (ASD).

4. Disease

Disturbances in our gut bacteria have been linked with digestive disorders such as Intestinal hyperpermeability (or Leaky gut), inflammatory bowel diseases (IBD) such as Crohn’s disease and ulcerative colitis, as well as obesity and type 2 diabetes.

A poor diet and Antibiotic disturbance of the microbiota can lead to disease, including the emergence of infections that display antibiotic resistance.

Our microbiota also plays an important role in controlling the growth of opportunistic pathogens and undesirable strains of bacteria that would otherwise cause disease and ill health. Our commensal or “good” bacteria compete with the “bad” bacteria to protect our health.



  • The human microbiome is largely made commensal or“good” bacteria and microbes which lives mainly in our gut and is thought to out number human cells 10:1.
  • These microbiota are symbiotic and we depend on them for our health and well being as much as they do on us.
  • Collectively these microbiota form an ecosystem – thought to consist of hundreds of different strains and species – which determine much of our health and well being. However disturbances to the balance of this ecosystem have been implicated in a numerous health conditions and diseases.