mmmm!
A hot topic on both AB and in the medical world particularly Oncology, but more work and studies need to be done.
NoM is correct, in that there is "some" and well reported evidence from prestigious centres, that fasting reduces the side effects of chemotherapy and perhaps causes reduction in the size of the tumour.
That is chemotherapy + fasting.
As far as rheumatic diseases are concerned, there is some suggestion, that some foods act as allergens (allergy) in the instigation of the auto-immune response and may be helped by elimination diets, which are quite different from "fasting."...