just speaking as a chronically ill disabled adult doctors in general (and GI) tends to blame the brain to gaslight patients and out of hubris related to "if i dont know the answer it must not be real" surrounding most medical professionals and their fields. once i managed to eat better my physical and mental health improved a lot well past the placebo period. thats also true of when i started working on my mental health so i agree it probably works both ways. and while ive definitely had psychology acknowledge theres issues with physical health that relate/worsen psychological issues ive never had any psych professional go "well psych cant help you in anyway theres only physical cures for this." they usually refer me to a physical health doctor and still help me manage the resulting stress/depression etc. that comes with trying to navigate the hellscape that is our healthcare system. that being said im in the USA so its supposedly not as dire in other places

a healthy diet can and often does include meat. and yogurt especially since it has probiotics in it. theres usually more of an issue with high carb intake than anything else. that being said its all dependent on the individual person and what their gut flora specifically needs and its pretty irresponsible to try and tell hundreds of people you dont know to follow a specific really restrictive diet. if anyone wants actual dietary advice your "best protection" is to do your own research, try things, trust your body, and if you can afford it more than anything else consult a nutritionist about your specific needs