when is a fast not a fast?

Hint -- this is like when Peter asked "when is a high-fat diet not a high-fat diet."

When Dr. Atkins prescribed a "fat fast" for people who are extremely resistant to losing weight, it was incredibly low in calories, and he only recommended doing it for a few days at a time.  It had enough fat to suppress the appetite, and it forced the burning of body-fat for fuel, because it certainly didn't supply enough protein to convert to a LOT of glucose.  I feel sorry for those on it who didn't have the metabolic flexibility or gut-bugs to get ENERGY from fat, and yet had to go about their daily business....

I assumed that the fat-fast was all about getting into ketosis ... until recently.  There are a few blogs where isolated posts give hints on why eating like this may promote weight loss by other pathways, too. 

In one of Peter's posts, he speaks of intestinal biota which prompt the brain to eat "fiber" and store fat, or to release stored fat for energy (so the host can go out hunting) ... and fat ingestion signals the latter.  The use of fatty foods during an intermittent fast (like drinking coffee with cream) is suggested by the Drs. Jaminet as "not counting" as food....

Here, too, is an explanation for the benefit of oil-swilling in the Shangri-La regimen!

Now we have this discovery that eating fat-with-no-carb spurs glp-1 production, which in turn turns off appetite and turns on spontaneous movement.  I find this very exciting.  In the average human, excessive energy "wasting" -- i.e., going to the gym -- is discouraged by our very beings (see Naturally Engineered); as a result, forcing yourself to exercise when you don't want to is more stressful and less effective.  But by this pathway, the urge to move is instinctive rather than a choice.  One gets the benefits of movement on the tissues and the mood-enhancing aspect of exercise in the brain -- all with no hunger or nasty cascades of BG and insulin.

So, yeah -- i now see the fat-fast as being a LOT more powerful than i believed possible, just reading Atkins.  ...I'll be sure to eat MORE CALORIES of it than he recommended, though!