The Basics

The human microbiome is the entire collection of microorganisms living on the surface and inside our body. The microbiome has various actions across human physiology including effects on immune system development, digestion, mood and detoxification reactions. Some of these microorganisms residing in the gut help create proteins for functions such as metabolising dietary nutrients (i.e. fatty acids, glucose and bile acids) and drugs, digesting complex carbohydrates and synthesising vitamins and other bioactive compounds.

The microbiome is extremely dynamic and can be influenced by multiple factors including age, diet, hormonal cycles, travel, therapies and illness.

The Complexity

The microbiome consists of an estimated 100 trillion microorganisms, containing up to 1000 different species, with a few dominant bacterial species being the major inhabitants. There are also yeasts, viruses and pathogens present. All these organisms perform multiple functions and are beneficial when balanced.

The Good, The Bad and The Ugly

There are no good or bad bacteria per se. Potentially harmful microbes only become dangerous once they start to take up too much real estate, outnumbering the beneficial ones. A microbiome containing too many so-called ‘bad’ bacteria and not enough (or the right combinations) of ‘good’ bacteria has been connected with increased prevalence/exacerbation of a range of conditions such as allergies, depression, anxiety, autism, inflammatory bowel disease, Crohn’s disease, rheumatoid arthritis, multiple sclerosis, obesity, type II diabetes, hypertension etc.

Dysbiosis specifically is the microbial overgrowth or imbalance that results in detrimental symptoms for the patient. An imbalance of microflora leading to symptoms may be due to colonisation with pathogenic bacteria, fungus and/or parasites. Typical symptoms include diarrhoea, gas, bloating, constipation, reflux, gastritis or abdominal pain. Dysbiosis can be the cause of these pathologies or simply an exacerbating factor.

Too Much or Too Little

Studies suggest that a more diverse group of gastrointestinal microorganisms is associated with improved health, whereas less diversity is associated with conditions of illness. The study of the specific species, their levels and the interplay between the different microorganisms is a hot topic among scientists right now. What is clear is that the gut microbiome and the human host, can work together to avoid microbial imbalance and the more diverse an individual’s gut microflora are, the better it is for the person’s wellbeing.


There you have it, an overview of the microbiome and why it is rightly a major focus in health and research right now. Next week we will focus on what you can do to maintain a well balanced microbiome and have greater health overall.

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