High alpha diversity and health (2024)

On and within you lies a vast and complex community of microorganisms known collectively as the microbiome. These microbes play essential roles in our health and impact how our bodies respond to disease in ways we are still uncovering. Depending on where you look on the body you will find a specialized community of microorganisms adapted for a given niche. The microbial community on your skin is distinct from what you find in your mouth and gut. The vast majority of your microbiome resides in your gut. High gut alpha diversity has been linked to a healthy state in so many studies that it has become common knowledge in microbiome circles. So often is the term thrown around that it is easy to just accept it and move on. But why is this the case, why do so many studies ranging from obesity to diabetes to IBD see the same pattern? Let’s take a step back and really think about this and start with the basics.

In its simplest terms, alpha diversity is a mathematical measurement of microbial richness in a given community (talking about the gut here). The more types of microbes you have in your gut the richer it is. This term is borrowed from the field of ecology where species richness has been proposed to correlate with the health of an ecosystem, as diverse communities may increase the stability and productivity of an ecosystem.

Now if you go to a microbiome conference, most gut microbiome talks will follow a similar initial format: alpha diversity was higher in healthy vs disease, beta diversity was different, these bugs changed ect. So it came as a surprise during my Ph.D. that the results I was seeing in my research really deviated from the norm.

At the time I was studying polycystic ovary syndrome (PCOS) a common cause of female infertility in which about 80% of PCOS women also have metabolic abnormalities. Dysregulation of the gut microbiome in PCOS is associated with the development of the PCOS metabolic phenotype. I was trying to understand the role that the gut microbiome plays in the development of PCOS. Using a PCOS mouse model, we found that exposure to a healthy gut microbiome improved the PCOS metabolic and reproductive phenotype. As expected, placebo mice had a higher alpha diversity than our PCOS mouse model. However, what intrigued me was that when we looked at the gut microbiome of PCOS mice exposed to a healthy gut microbiome their alpha diversity was not similar to the healthy mice, it was similar to the PCOS mice which displayed the reproductive and metabolic phenotype. Furthermore, healthy mice exposed to the PCOS gut microbiome never showed any PCOS reproductive or metabolic phenotype, but they did have an alpha diversity similar to PCOS mice.

So hold up, we have PCOS mice who metabolically and reproductively looked like healthy when exposed to a healthy gut microbiome but their gut microbial alpha diversity was similar to a PCOS mouse displaying the PCOS like metabolic and reproductive phenotype aka low alpha diversity!? What gives!? This turned out to not be a random event as we were able to repeat this observation in a separate study.

What is the deal with high alpha diversity and a healthy state? The gut microbiome is suggested to play many roles in human health and development, whether it is through direct microbial interaction with the host or through microbial metabolites. The gut microbiome has been suggested to be involved in the synthesis of vitamins, fine tuning of host immunity, fermentation of insoluble fibers, integrity of intestinal barrier, modification of bile acids, neurotransmitters and hormones. Those are a lot of roles and the players involved vary. This suggests that increased diversity is associated with increased health because with increased numbers of microbes you get an increased chance of all the right players being present to properly turn the wheels in this human machine. However, it could be that you do not need the increased diversity per se, but just the presence of the right players to allow you to properly turn the wheels as our PCOS mouse study suggested.

So maybe that old quote is right and we just haven’t been listening.

It’s not the quantity of friends you have it’s the quality of friends you have