Sugar raises internal inflamation. I follow The Yeast Connection Handbook, by William Crooke, Md. It's tied to leaky gut and the yeast which resides in our gut which puts out waste transferring throught the lthinning gut linings and into our bloodstream. I semi follow the maintanence plan, basically all I eliminate totally is processed sugar and I eat gluten in moderation. The hard part is the 2-3 month detox to starve the yeast colonies in your body . During that period zero sugar, processed or natural and zero carbs. This detox worked for me, the internal nervie sensations stopped and that was 3 years ago. It's a quick and simple read based on what yeast is doing to our bodies. Sugar, among other foods feed yeast.
I don't have muscle spasm or deep cramps, however nerves all over my body went crazy for years: stinging, zapping and itching. A doctor will look at you but can't "see" how you are feeling. These sensations were driving me insane, sleep was fitful at best and I was sleep deprived as the sensations were severe.
Intresting that you mentioned an itching band around your midriff. You don't mention a rash, but I also have a form of eczema, Grover's disease which targets the front and back torso area, for me especially around the midriff front and back.
Arthritis can make your hands draw up like claws, arthritus is inflamation in the joints. Leaky gut raises inflamation in the body. Eczema is also an inflamatory disease.
I haven't had food testing for allergies, have you looked into that?