There is no single ideal gut microbiome that is healthy for everyone.
Healthy people can have very different combinations of gut microorganisms. The microbiome also varies with age, diet, medications, lifestyle, environment and geography.
So what makes a microbiome healthy?
Scientists look at several features.
Microbial diversity is one of them. A diverse microbiome contains many different types of microorganisms. Higher diversity is often associated with health, but diversity alone does not tell us whether a microbiome is healthy.
Microbial function also matters. Gut microorganisms produce metabolites and interact with the immune system, intestinal barrier and human metabolism. Different combinations of bacteria can perform similar useful functions.
Stability and resilience are also important. A healthy microbiome should be able to adapt to changes and recover after disturbances.
Age adds another dimension.
Research involving more than 9,000 people found that gut microbiomes became increasingly individual from mid-to-late adulthood.
Among people over approximately 80 years of age, healthier individuals continued to develop more unique microbiome profiles. This pattern was not seen to the same extent in less healthy individuals.
This means that a healthy microbiome in later life may not be one that looks like everyone else’s.
There is therefore no universal list of bacteria or single microbiome score that defines health.
A microbiome result is better understood as a combination of its composition, diversity and function. Age, diet, medications and overall health also need to be considered.
For longevity medicine, the goal is not to make everyone’s microbiome the same. The more useful question is whether an individual microbiome is associated with healthy function and healthy ageing.
