Mushrooms contain a healthy antioxidant called ergothioneine. But for people with a SLC22A4 genetic variant, this antioxidant can be too much of a good thing, leading to intestinal problems. Check your genetic data to see if you carry this mushroom intolerance variant.
The IL17 gene codes for an important part of the immune system. When it is overactive, IL-17 can contribute to the risk of autoimmune diseases including rheumatoid arthritis and inflammatory bowel disease.
All of the general advice, fix your gut, eat more fiber, eat fermented foods, avoid sugar, grains, dairy, etc., may work for some but not for everyone. Take a good look at some of the genes that affect our microbiome.