Fast this way is a primer on fasting, but it is entwined in the author's personal experience when he did a long-term fast that included a Shaman and living in a cave. It is not a traditional health book that focuses on step 1 is ________, step 2 is _______, etc. There is some "how-to" content and the book does go into the science behind fasting, but that is sometimes in the background. The author does shill a bit for "bulletproof coffee" which is basically the idea of drinking coffee with MTC (coconut) oil added to it. Bulletproof Coffee is a brand that the author sells, but you do not have to use that brand in order to make the concoction.
The book gives tips for how to do different kinds of fasts, from the easiest, intermittent fasting (which basically amounts to skipping dinner or breakfast so you do not eat for 12-16 hours), to the harder multi-day fasts. He also gives you an idea of what to expect from your body when you do the various kinds of fasts. So, if you are interested in the concept of fasting and are looking for something that will give you both an idea of how to do it and what you can expect your body (and mind) to go through, this is a good book to read.