You know how people talk about probiotics, but no one really tells you what those are? Well, they're bacteria, and yeast, and for all I know, maybe some other things, but they're basically microorginisms that process food. The "pro" part refers specifically to the beneficial ones, cause some of them can be pretty harmful. For example, Clostridia is linked with autism, depression, and so on, cause all of these things affect your brain too. The video explains more of this stuff.
This is why foods go bad after a while. If the food never dies, it was never alive to begin with, and after a lot of processing, it might preserve shelf life, but now it's very lacking health-wise. If you're having digestive issues, try fermenting food (letting bacteria digest the food it's on, and grow) and then consuming them. It should do wonders, but if you're already unhealthy, pretty much anything you do that's healthy is going to negatively affect you (healing crisis) if you're not careful.
The bacteria in your gut are basically doing the same thing, and some of the bacteria from these foods can end up living in your gut. Though, these bacteria are not necessarily allies with each other. Some will effectively wage war and win out over others, so some might die off pretty easily. Kefir, for example, has some pretty strong bacteria, and that can take over and dominate your gut, kicking out some of the other bacteria, which is probably a good thing, judging on the results people get.
Aside from all that, you might really want to consider heavy metals and other toxins, and getting them out of your system somehow. Chelation, perhaps, or even sweating them out. You might also try a hot bath in something that draws them out. Either way, heavy metals can cause a multitude of problems. Including, once again, autism. If you have mercury fillings in your teeth, get that removed, and make sure it's safely removed, cause it can be removed very harmfully. That stuff releases a steady stream of mercury into your system, poisoning you for years to come. Also avoid water with fluoride, which includes your water supply. If I were trying to get rid of some of these, and I wasn't broke, I'd take calcium (makes muscles contract), boron (chelates fluoride, but also important for healthy cell walls, and helps the transfer of calcium and magnesium), then take a hot bath in magnesium (makes muscles relax), and then get out and sweat up a storm in an infrared sauna. Maybe even get back in the bath after that. Make sure to drink a ton of water during this.
For chelation, there's a lot of specific things here, so I'll just give an overview. Some of the toxins are stored in soft tissues and the like, and certain foods or supplements draw these out, and they end up in the blood stream. The nice thing about sweating it out is that it comes out on the outside, but chelation involves drawing them out on the inside, where they end up in the blood stream, which can really harm you if you overdo it and don't have something to bind to them and lead them out of the body. So, combine a couple of things here. Something that draws them out, and another that binds to them. Don't do too much at once.
Good luck, user.