[mtqwerty]

I did a project during undergrad looking at the connection between the microbiome and food cravings. Mostly anecdotal evidence from what I could find but the theory makes sense conceptually. Stay with me..

The microbes that live in the gut can influence the way we feel in a bunch of positive and negative ways (could give sources but just google it).

Microbes are just little machines programmed by evolution. They're designed to optimally survive in a specific environment and get better at it over time. Most of the microbes in the gut have been with us for a long time so they've done some evolving.

Microbes don't actively think but their behavior and metabolism are still optimized by evolution. They can react to avoid being killed, to eat and to reproduce all without "thinking".

Each microbe also has a pretty specific diet. The microbes that enjoy greek yogurt don't often like chicken nuggets.

Microbes that could influence their host to consume food the microbes liked would be more fit to survive. Same thing for influencing their host to consume less food they dislike (or a competing microbe likes).

Influencing the host sounds complicated but it could be as simple as increasing the concentration of a byproduct when food concentrations of the environment are low. That byproduct could make the host tired or give them a stomachache or whatever else. With the brain connection, the possible range of these effects is broad.

If this trait was developed at anytime, it most likely got passed down to present day microbes.