I know this won't be popular to say, but we found evidence that a very clean organic vegan diet may be the best option for Parkinsons.
My husband and I did a lot of research into this because his mother was diagnosed with a very rare form of it. We read a bunch about protein interfering... I don't remember a lot of it now, but if you look it up, you'll find the info. Unfortunately, my mother-in-law never tried (and her caregivers have never tried) feeding her different things to see what helps. Now she is in a nursing home near death.
So, as I said, it may not be a popular thing to say on here, and generally speaking I no longer endorse a vegan diet, but I really think there might be something to it in this case.