I guess it depends where your protein intake is to start with. I do better with a more steady ketogenic ratio, I think that sort of limits my personal comfort with fasting. A facebook page I'm on follows Dr. Fung, and they'll talk about protein backfilling, making up for the lack of protein during fasting with some extra. This hasn't really worked for me, I'll feel better during the fasting itself, but the refeed is by definition less ketogenic, and I don't find I feel as good then. Right now I'm doing a carnivore keto experiment, carbs only from heavy cream, so my protein intake can go up 20-30 grams or so without the diet being less ketogenic--I've been thinking I might do an experiment with fasting again just to see, with my protein a bit higher I'd be more comfortable with not trying to make up for the short period without protein.

If you look at calorie restriction--a group of researchers have clamped on to fasting's effects on stem cells, so they're doing study after study that shows similar effects on various stem cell populations. Fasting is sexy right now, so we see these studies. There is similar data for caloric restriction, since the two approaches have similar health/longevity effects, maybe that's not surprising. Since we've got that one little mouse study showing a life-extending effect for a ketogenic diet, I have to wonder about stem cells in that model.

In rodents, the calorie restriction model seems to depend on whether the animal's usual diet is one that would make them obese/diabetic. A question that comes up a lot is, do all these various approaches extend normal lifespan, or do they just revert things to normal? I like this image;



People who were always lean, and calorie restrict themselves to skeletal status, I suspect that's probably just as unhealthy as it looks.

There is obese and then there is weight-reduced obese. Dr. Fung concentrates on the habitual diet's effect on metabolism etc., but there are profound effects on metabolism that will vary from person to person that probably interact with the diet but have an existence of their own. My best guess is that if you respond better to eating a certain way, in weight loss, appetite and energy, then it probably really is better for you, whatever these various fasting studies say.