I am pretty new to this, and understand that dietary fat will not create an insulin response. Hence, Dr Fung has said that a “bulletproof coffee” “fast” (a couple cups a day, to prevent hunger) will not reduce the benefits of fasting (when flat-out asked about it by Dave Asprey).
However, since the difference between fasting and CRaP is zero vs. “some” calories, why does a “fast” with dietary fat (butter & MCT oil) not reduce one’s metabolism?
I am no expert either. But when Dr. Fung talks about fat consumption, he is talking about insulin response. There are a lot of other benefits to fasting besides insulin response and diabetes reversal, and a fat-eating fast would not give you (some of) those other benefits. Autophagy comes to mind. Obviously weight loss based upon eating too many calories would also be a problem, but one would almost certainly be less hungry so there would be less eating. I would guess that there would still be some weight loss, but certainly not as much as a water fast. It will probably depend upon the physical state of the person exactly what would happen.
I greatly prefer a water fast to a fat-eating fast, so this is an academic question for me. I am thrilled with the concept of autophagy, and I have seen healing unrelated to diabetes when I fast.