M51, cancer survivor, in remission and healthy

I have acquired IBS after chemotherapy in 2015. Can't eat anything with garlic or onions. Lactose as well but I think that might be just normal aging. However neither of my parents are lactose intolerant.

I have been treating my IBS by going on a FODMAP restriction diet. That works well enough but occasionally things will sneak through and I will have two days of diarrhea and mild fatigue. It's just annoying and reduces my quality of life. Also generally I think my brain function is not as good as it could be if I had normal bowel function.

I talked to a doctor who runs an FMT clinic about this and he said that he has treated cancer survivors before and had good results. But my GI doctor doesn't think that FMT will do anything for me at all and she would rather I didn't do this. But my GI doctor is not an oncologist. When I have talked to my oncologist about this before they said that it was pretty likely that the chemotherapy did mess up my biome but they didn't offer any suggestions for actually fixing it.

Really I'm just curious what the science looks like right now.