Fruno: I disagree with some of your points:
There’s plenty of solid evidence of the health benefits that accrue with much longer fasts than 2-3 days, particularly for reversal of degenerative disease related to metabolic dysfunction. (Cancer can be considered a metabolic disease, see Warburg Theory, but that is a longer discussion).
Metabolic rate is driven more by your activity level than your food intake, in fact with the increased adrenalin levels that come with an extended water fast, and intensive daily exercise I actually boost my base metabolic rate while fasting.
After reading plenty of studies, and my personal (n=1) experiments, it is not true to state “Your body will always try to regain lost weight due to extended fasts”. You could claim some people will, but not always, and you’ll find those that do gain weight over-eat between their extended fasts (back to my original point).
For many people. especially those who are not fully fat adjusted, a 48hr fast will barely burn off their muscular Gylcogen stores, and their Ketone levels will not rise sufficiently for many of the more powerful health benefits (I’m not referring to weight loss), which typically require maintenance of a GKI level <1 for an extended period.
I believe that Dr. Fung’s reticence about limiting fasts to <7D, outside of a clinical setting, is not because longer fasts do not have therapeutic value for certain conditions, but that they can be dangerous for some, particularly those with underlying health issues, without professional medical oversight (plus his potential liability if he recommended that).
I’m pleased you have attained your weight loss goals without fasting, as you say we are all different and I’m not on this site to promote long term fasting for anyone else, but remember that others are not doing Keto / IF for weight loss at all. I kept my father alive for 12 wonderful years by careful use of a Keto diet and IF, after he was diagnosed with incurable metastatic prostate cancer and given 18 months to live.
Personally, I maintain a single-digit body fat % and a >40% muscle, and exceptional blood markers (over 50 measures every 12 weeks) through a combination of a LCHF diet, OMAD, and quarterly long fasts of up to 21 days. Plus lots and lots of exercise, of course.