We all know people who act very differently depending on the company they find themselves in. They can be delightful in some circles, and obnoxious in others. The same principles apply to the microbes in our bodies—our microbiome. They have important roles in digestion, immunity, and health, but none of them is inherently good. They can be helpful in one part of the body and harmful in another, beneficial when paired with certain partners and detrimental when teamed up with others.

This means that, as I’ve written before, there’s no such thing as a “healthy microbiome”. Context matters. And contrary to what some companies might tell you, we’re still not very good at looking predicting what any particular community of