You will have to ask Dr Virginia Vetrano who worked with Shelton in Austin Texas regarding his premises (she is a friend of mine on facebook).
It was Dr Stanley Bass I believe who quoted the figure of 50,000 fasts but many consider 30,000 fasts supervised by Shelton as being more accurate.
Dr Keki Sidhwa ND DO, who was a disciple of Sheltons, supervised 26,000 fasts of varying lengths during his career here in the UK, so 30,000 isn't unrealistic.
Shelton was more than just a Naturopath, as he held these credentials from varying Schools and Colleges of health: D.P., N.D., D.C., D.N.T., D.N. Sc., D.N. Ph., D.N. Litt., Ph. D., D. Orthp.
You also mention: "when it comes to the mechanisms of fasting, the knowledge of how it works and why -- it is seriously lacking."
..................and my answer to that would be how many animals in Nature resort to laboratory analysis to determine their blood counts, or kidney/liver function or even for low levels of electrolytes.? Mostly irrelevant.
However, a modern counterpart for the scientific evidence of fasting is from Dr Joel Fuhrman MD and a friend of Sheltons.
You are speaking as someone who has a "medical mentality" as only medical personnel need to know the details of physiology that you speak about. Such details are irrelevant to a faster as part of their programme in the pursuit of health and wellness.
Actually, Shelton worked a seven day week for decades and burnt the midnight oil when writing his many books, otherwise they would never have been written. This was also the reason for his demise and, sadly, he din't practice what he preached in the zealous pursuit and promotion of his "cause".