If you're interested in digging into the people that were doing this, they had a website dedicated to everyone telling their stories of how they went about their own individual journeys.
The website was called thepowerofpoop.com and looks like it's gone now, but is available on the wayback machine including individual articles and images.
I would go back to at least 2022 .. I think they possibly got in legal trouble at some point and started taking things down.
I think the fecal transplants help to essentially seed your gut with healthy bacteria, which makes adapting to the proper diet easier when your body isn't constantly fighting you.
Microbiome transplant therapy is a domain full of grifters right now who will push it to vulnerable populations desperate for hope, like parents of autistic children. The real research results are much less promising for difficult conditions.
More recently, a study finds The modulation of the gut microbiota using MTT in ASD has shown beneficial and long-term effects on GI symptoms and core symptoms of autism[3]
[1] https://gutbrainaxistherapeutics.com/pipeline/#clinical-tria...
[2] https://link.springer.com/article/10.1186/s40168-016-0225-7
[3] https://www.tandfonline.com/doi/abs/10.1080/19490976.2025.24...