@Derekthecat My short answer is that nutritional approaches have had no effect on my ME/CFS symptoms, but both a positive, and negative, effect on other issues that have developed over the years. Here are a few highlights, and "lowlights".
Removing grains (particularly refined grains) and starches has virtually eliminated my GERD. Also, grains and starches seem to have a neurological effect on me, because when I eat them, I regularly stumble, and my hands go numb. The removal of grains dramatically reduced the swelling in my joints, especially my knees, associated with rheumatoid arthritis. Gluten, in particular, affects my thyroid, and makes my hypothyroid condition much worse.
I have many digestive issues -- IBS, SIBO, leaky gut, extreme bloating, alternating hard stools and the opposite. I've tried both the FODMAPS and GAPS diets. Removing FODMAPS was only a short-term solution, because my symptoms returned as soon as I added back the restricted foods. The GAPS diet initially seemed helpful. Within days on Phase 1 (very restrictive), my joint issues were completely gone, as was my bloating. However, my "smeary" bowel movements turned to chronic constipation. I didn't have a bowel movement for several months, and resorted to a weekly enema while waiting for things to return to normal. They didn't. And, my sleep issues worsened. I also lost too much weight -- 15 pounds on a very tiny frame. I was delighted with my completely flat stomach (no bloating), but the diet was so low-carb, I wondered what was feeding the the healthy bacteria in my large intestine. Every time I tried to add in foods in the later phases of the GAPS introduction diet, my bloating returned. And, the longer I stayed on the diet, the worse I felt. I decided I was among those who need a higher-carb diet than that allowed on strict GAPS.
Adding a few starches made my bowel movements more normal, and helped to restore a healthier sleep pattern. But, the bloating over my small intestines returned immediately (SIBO), although not as bad as before. Bloating in the large intestine area still hasn't returned, so in that respect, I think something has changed for the better -- possibly healthier gut flora from all the fermented foods and probiotics.
Unfortunately (or fortunately, depending on how I look at it), the GAPS diet definitively diagnosed a mast cell/histamine issue. The fermented foods filled my "histamine bucket" to overflowing. Now, my diet is even more restrictive while I deal with an excess of histamine -- absolutely miserable symptoms. I think GAPS is very good for healing a leaky gut, but those with histamine issues should use carefully-chosen probiotics instead of fermented foods, at least at first. The one higher-histamine food I'm still consuming is homemade bone/meat broth which is supposed to be very healing. I simmer mine for only 12 hours, freeze it immediately, and thaw it just before drinking to limit the histamines.
So for me, a hybrid of a low-histamine/autoimmune paleo (AIP)/GAPS diet seems to work best. I'm currently testing various "safer" starches to see if any might do more good than harm. The take-away message is that the "best" diet for GERD and leaky gut depends on the individual. Trust your "gut", and if something seems to be causing as many, or more, problems than it is solving, try something else.