The notion that the state of our gut governs our state of mind dates back more than 100 years. Many thinkers and scientists believed, that accumulating wastes in the colon triggers a state of “auto-intoxication,” at which the poisons emanating from the gut produced infections, that could be linked to depression, anxiety or psychosis. But is it really true? Do we have a cumulative scientific evidence backing the hundreds of on-line articles presented on popular health-and-diet portals? What are the other diseases related affected by lower quality of gut microbiota?
The word “microbiota” represents an ensemble of microorganisms, located in a previously established environment. Human beings have clusters of such bacteria in different parts of the body – on the surface and deep layers of skin (skin microbiota), in the mouth (oral microbiota), or in vagina (vaginal microbiota). Gut microbiota (also called gut flora) is the name given to specific microbe population living in our intestines.
On the figure above we can see, that research on the effects of gut microbiota on various diseases is relatively new topic. The research papers investigating the connection between obesity and gut microbiota are being published only since 2004. So far, there is 536 papers about relation between obesity and gut microbiota. Top paper for these keywords is “The gut microbiota as an environmental factor that regulates fat storage.”, with 312 citations. The author who contributed to most articles is Patrice D. Cani. Country with the most publications regarding this subject is USA, followed by France and Belgium.
The second most popular topic in this field is the relation between gut microbiota and diabetes. On the above figure we can see, that the papers about this topic started to be published in 2006. The number of papers is rising rapidly and as for now, 271 research papers describe the connection between diabetes and gut microbiota. The most cited paper in this category is “Functional interactions between the gut microbiota and host metabolism.”, published in 2012 in Nature. Patrice D. Cani is the author with the most relevant contributions, also in gut microbiota research in the context of diabetes. On the figure below, we can see that the countries with the broadest research in this field are USA, Belgium and Sweden.
Researchers also focus on the ways, the gut microbiota affects the cancer development. The most cited paper in this field is “The gut microbiota shapes intestinal immune responses during health and disease.”, with 203 citations. The highest frequency of research efforts comes USA, followed by Italy and United Kingdom.
In the beginning, we have metioned the concept of gut microbiota affecting our moods, and even development of diseases like depression or psychosis. Looking at the first figure presented, we can see, that currently there is minimal research carried out in this field. So far, there are only 33 research papers studying the connection between gut microbiota and depression. However, most of them are reporting the results of positive correlation. The most cited paper is “Melancholic microbes: a link between gut microbiota and depression?”. Because science is a knowledge acquisition system govern by cumulative evidence, we should wait for the paradigm to grow a bit. before making general statements about our gut microbiota affecting our psyche.
When we look at the numbers, it is obvious that this field of research is quite young. However, given the growing trends in research focusing on relations between microbiota and cancer, obesity, or diabetes, we can tell, that the investigation of gut microbiota’s links to depression is potentially very promising and currently rather untapped field of research.