Abstract:
Part three of this four-part series continues to evaluate the relationship between the human species and the human gut
microbiome. It focuses on whether their relationship is symbiotic, parasitic or somewhere in between. The possibilities,
based on animal studies, are explored and compared to scientific facts proven in human beings. In particular, close
attention is paid to the relationship between the gut microbiome and central nervous system, and the effect this has on
human behaviour. This relationship is termed the ‘microbiome–gut–brain axis’. Through a number of pathways, the gut
microbiome has an influence on stress (both acute and chronic), anxiety, loneliness and depression, as well as on odour
and attraction. It has also been associated with the development of neurodegenerative diseases such as Alzheimer’s
and Parkinson’s, and with associated cognitive decline. Since the common treatments used for these conditions are not
equally effective in all patients, it is vital for clinicians to explore other avenues that could be used as therapeutic targets.
The gut microbiome, in particular, requires further research in order to aid the development of future therapies for certain
conditions. The concept of the organisms in the microbiome controlling the mind of human beings is relatively new, but
such control has been demonstrated through multiple examples in the animal kingdom. Animal studies in this regard have
shown promising results, but human studies are infrequent and often present disappointing results. Randomised control
trials in human beings are greatly needed, either to prove or to disprove, the effects of the gut microbiome on complex
psychiatric diseases.
