Earlier quoted context omitted.
It makes sense for chocolate given that cocoa flavanols are prebiotic fiber for GABA-secreting bacteria which of course affects the parasympathetic nervous system.
The paper didn’t say that the microbiome was driving food preferences. It measured some bio markers and some dietary preferences and claims some correlation. The correlation is that what you eat fuels the microbiome. So your diet influences the microbiome by fueling or starving different bacteria. Complex theories about causality going the other way through complex chains of flavonoids to bacteria to neurotransmitter…
What's the theory now? I didn't propose any specific theory -- just noted a mechanism of influence.