You will find no "gold-standard" RCT (Randomised Controlled Trial) on fasting because the Medical profession use and believe in a totally different concept to disease-causation. Those who have used fasting in the past will tell you that the body is a unified organism seeking Homeostasis or equilibrium. If one or more body-part/s are affected by disease, it is because the whole of the body is affected and not just the localised area: cancer being a case in point here.
Shelton by the way didn't just rely on his experienced forebears in the use of the fast, but on his own experience spanning from the 1920's and well into and up to the 1980's.
Modern day counterparts would include Dr Joel Fuhrman MD whose book "Fasting and Eating For Health" lists quite a number of scientific references in support of long-term fasting (up to 30 days) on pages 227 to 244.