Earlier quoted context omitted.
The microbiome might have some modulating effect, but the fidelity of gut-brain axis communication isn’t so strong that our gut microbiome is driving us around with highly specific inputs. The theories for how gut-brain axis modulation works include altering the balance of nutrients that get absorbed and modulating the vagus nerve, primarily. For someone with autism it might be possible that altering some of these ba…
I’m not going to pretend to be an expert here, but I remember a study that found gut bacteria composition predicted whether or not an individual was chocolate-craving or not in individuals eating identical diets: https://pubmed.ncbi.nlm.nih.gov/17929959
They didn’t run any experiments trying to change the diet or microbiome. They just correlated dietary preferences with some markers that might be correlated with the microbiome.
The paper does not say anything about how changing the microbiome might change preferences. The simplest and most well tested explanation is that dietary preference are driving the microbiome.
There’s a lot of woo-woo microbiome discussion out there that misses the really obvious basics of how the microbiome comes to exist and thrive: What you eat is what the microbiome eats, so changing what you eat will change the composition of bacteria that thrive. People who prefer chocolate are correlated with people who prefer sweet diets. High sugar intake is proven to alter the microbiome.