Doesn't everything we consume?

Probably, hence the study to confirm that assumption. It is usually just ignored though, with nutritionists focused on the direct effects of ingesting food and not noticing how our biome adapts and the indirect effects this causes.

Some things have much more of an effect than others (stuff high in prebiotic fermentables)

> They suggest there are substantial impacts of a single food or beverage on the human gut biome.

How would the bacteria survive and procreate?

My hypothesis is that they need to eat something.