Dean - I believe Phinney may have been referring to the situation when one is fully efficient at using fat for fuel during endurance events or activities. I'd have to see more context to his statement. Know that Steve Phinney and Jeff Volek have been working with endurance athletes to enable a successful adaptation to fat as primary fuel. Some distance runners and cyclists have experienced longer event duration without having to consume glucose like many distance runners do when competing over a period of a few hours. In a glucose fueled individual, this fuel consumption during the event prevents them from hitting the wall.

I believe it's reasonable and we must separate fat-adapted from ketosis, as I believe fat-adapted means that one is able to easily burn fat as fuel as much as glucose. From personal experience, I may be out of ketosis, but I can still move back into fat burning rather quickly nowadays either with a short fast or diet using strict low carb or carb elimination for a period of time. I've also noticed that when I'm fasting (doing IF), I move through the initial sensations of hunger very quickly and no longer experience hunger at around 2-3 days into the fast. So, even if I'm not in ketosis, I can move quickly into ketosis and fat burning as primary with little time and effort. I know others will have views on this, as each one of us is a snowflake (i.e., one size does not fit all in terms of how each one of us responds to diet). For me, I like to stay in fat burning mode most of the time. As I've mentioned before, I call fat burning mode "burning clean."

Another source who may interest you is Amy Berger. She has a series about ketosis on her blog, and she goes into a lot of detail. Here's the link to her main page: http://www.tuitnutrition.com/

Here's the link to her keto blog: http://www.tuitnutrition.com/2015/0...carbs-stop.html

Here's the link to a shortened version: http://www.tuitnutrition.com/2015/0...carbs-stop.html

And another link that Janet recently provided on another thread: http://www.tuitnutrition.com/2016/0...-a-ketard2.html containing this quote, "You can be in ketosis and not lose body fat, and you can lose body fat without being in ketosis."

And here's part 1 of the 3 part series of blogs: http://www.tuitnutrition.com/2016/0...-a-ketard1.html

She also has just published a book, "The Alzheimer’s Antidote: Using a Low-Carb, High-Fat Diet to Fight Alzheimer’s Disease, Memory Loss, and Cognitive Decline," which I'm currently reading and it goes into a lot of detail on ketosis and fat burning. Really good stuff, much of which partly addresses your original question.