Summary of the most advanced Medical Research
Thanks to David for pointing all this out. Almost all the most advanced research is pointing towards the gut as the source of all the problems and health issues in humans. it’s more than insane if you full keep up with all the research on just how much bacteria can alter humans. Bad bacteria causes schizophrenia, bipolar, Celiac, Crohn's, Parkinson's, etc all related and correspond to genes over-actively attacking bacteria... but the bacteria has to be present or there's no activity.
I originally (5yrs ago) couldn't find any info that said bacteria modified the brain "memory" biology, since then they have published a decent number of reports on how memory is dependent on bacteria and can be better or worse due to differences in bacteria. It's the long term problems that cause the diseases, each one of which is literally a 10-20-30yr slow progression disease
So far, the newer research says:
Crohn's disease is two bacteria and a fungus, almost impenetrable biofilm that the immune system attacks but ends destroying the intestine walls in the process because it's so sustained and aggressive attacking the biofilm.
Schizophrenia is a totally messed up intestine bacteria balances; effecting nickel transports, energy pathways, nutrient transport, repair, etc.
Parkinson's has been linked to the same C3 pathway (control pathway for enzyme tagging bacteria in the intestine and pruning synapses in the brain) as schizophrenia, autism, etc.
Celiac is linked to autism and M.S. (higher numbers of people have multiple diagnoses)
Autism is being linked to the enzyme that tags bacteria for removal, and that same enzyme tags synapses in the brain for removal... Hyperactive immune system targeting bacteria overload in the intestine increases synaptic pruning in the brain, bad side effect of the bacteria... Can have same nickel, metal transport impairments as schizophrenia, etc.
Bipolar is just a different area of the brain that gets damaged, corpus callosum (connects both sides of the brain), similar to schizophrenia in the brain's synapses are disappearing but genes seem to control which areas are more adversely effected by the higher pruning rates and/or damage from neural toxic effects of metals and less repair processes going on, lower energy available, etc.
Alzheimer's is a fungi differences, you can't get Parkinson's and Alzheimer's, you can get one or the other depending on the fungi and bacteria... very long setup time, two or more decades until symptoms show up.
Systematically, the whole body's repair processes are being impaired in all of those diseases and diabetes, which has been shown to lead to earlier dementia too, so it gets lumped into these brain disorders now.
Lower energy, chronic issues leads to brain and anxiety (immune system upregulated by norepinephrine hormone in the body, anxiety in the brain) issues.
It's all pointing to bacterial biofilms and other imbalances in bacteria/fungi. As fungi can regulator or dysregulate other bacteria balances. Viruses also effect the genetic expression of bacteria and can cause mutations to make bacteria more harmful to the body as they become toxin producing when fighting off a virus that is attacking them.
Amazingly complex but ultimately just gut bacteria, fungi (candida/yeast) imbalances.
The problem is all of this is variable to the person, they can have kidney dysfunction from this or thyroid dysfunction or pancreas dysfunction... any of which can lead to other problems. So, people trying green tea extract can die of liver failure or other health problems like cardiovascular disease due to how little exercise they get and the accumulating years of disease/dysfunction.
Probiotics are truly all you need but they don't even know all the bacteria that help the intestine... They are missing entire familes of bacteria that they are only now realizing exist. They only know about the easy-to-grow bacteria.
To live longer, you need to exercise 30-40 minutes of intense (running is considered intense) 5 days a week. That also should put most of your body into functional conditional, doing that for a long time leads to your body being 9 years younger at the cellular level, as defined by the telomere lengths.
If I was going to recommend diet/exercise to someone with a disease, I'd walk them through a recovery process they couldn't mess up. Set guidelines for cleanses, when to take cleanses, how to avoid people with the same health issues that will re-infect you, etc.
It's a messed up world, humans were never meant to be around hundreds of strangers every day... We're brain-functionally adapted to socializing with ~200 people in a group, not 2000000 people in a city. Bacteria on the other hand thrives when it's easy to hop from host to host, same goes for fungi, viruses, etc.