Jason Fung explains his theory of type 2 diabetes / metabolic disorder, and how it is addressed by fasting, in detail in episode #59 of Peter Attia's "The Drive" podcast [1].
The review of Fung's "The Obesity Code" on Red Pen Reviews [2] details some serious flaws in the scientific claims in the book related to calories, insulin, and fasting, and their relation to obesity and fat loss.
Relating to nutrition/health/longevity, they aren't books, but I've found the podcasts, blogs, YouTube videos, and even tweets by Rhonda Patrick (FoundMyFitness), Peter Attia (The Drive), Stephan Guyenet, and Chris Masterjohn quite enlightening.
He did write The Complete Guide to Fasting, which is excellent and covers all the science behind it.
There is also Delay, Don't Deny: Living an Intermittent Fasting Lifestyle by Gin Stephens which is basically One Meal a Day, however she includes links to all the reports to everything she talks about in the book and yes, she actually read them and encourages others to do the same, not just believe what she says.
There's always the fasting subreddit's wiki that has links to other info: https://www.reddit.com/r/fasting/wiki/fasting_in_a_nutshell
I have been trying fasting on and off for about 6 months and I can see results, but I have not bothered to check the theory behind it at all.
If anybody would like to recommend some books on nutrition, body aging and general health regarding food, bring it!