The microbiome needs no introduction – it has been several years since you could pick up a biomedical research journal and not run into an article on possible connections of human gut bacteria and disease. There were thousands of such papers last year alone. But it’s a very hard field to work in. You can establish correlations between certain gut profiles and some diseases, but causality is another matter. Do the bacteria cause or exacerbate the disease, or does the disease give you an altered gut bacteria profile? Or neither? There’s no particular reason that they should be connected at all (which is an option that our human brains are not always ready to consider, frankly). It’s worth remembering that we don’t even really have a baseline: there is no agreement on what a healthy human gut microbiome looks like, how that might vary depending on diet and environment, how many such microbial states might be considered healthy, and how much deviation from these would be considered acceptable.
Read more at Science Translational Medicine