This is some real "duh" stuff: of course gut microbes do, you are what you eat.

People with coeliac are often depressed. Sugar gives a rush and destroys food<-->dopamine. For autism, there's the very questionable "parasite" treatment.

Also, reducing acidity works wonders. Even Tesla swore by it.

If anyone's interested in "fringe" nutrition stuff, look up Aajonus Vonderplanitz. A lot of poeple will reduce what he said to "carnivore diet" but it's much more than that. Ray Peat, similarly.