Seeing if we are fat adapted isn’t so easy, I guess an active person can tell but we less active ones… The experiences differ. I saw a few ideas here and they usually don’t work for me. My hunger changed but there are many factors and fat adaptation isn’t the most important regarding how long my satiation lasts, it’s mostly about what and how much I eat.
I had two milestones. The first was 7 weeks into keto, my hunger and satiation suddenly changed for the better, no more annoying impatient super strong hunger!
The second happened way, way later (but I went off keto all the time as my previous, not very carby woe felt about the same, just easier. still, changes happened) and I don’t lose and gain water weight since that time (it was always +/-4lbs/2kg when I changed between ketosis and not ketosis before. my weight is surprisingly stable. I think it was half of this for months before becoming zero but I rarely weighed myself in those months and the difference is so small and I am a human with a theoretically changing bodyweight so I am not sure). As I never was particularly active, I didn’t notice anything there. Until the last year but multiple things happened at once, maybe it’s all due to my carnivore trials and not stopping my cycling for months in winter… I got significantly better, no doubt. I stopped weightlifting for years (and I still was so weak when stopped) and now I am worse than before my break and improvement is slow, I don’t see a positive effect there yet.
My energy level always were lowish, only my carnivore times could change that (not right away. it gave me zillion instant benefits, this serious one took time, not surprisingly), this change was definitely long after I lost my water weight changes so I am sure extreme low-carb was the key.
I think my hunger changed around the second milestone too but it was more gradual. The first change was very sudden.
I am not sure it helped any but here, my experiences, they may be interesting for someone. I always like to read how individual we are.
I personally don’t want to go over 72 hours but I feel the need to eat very very nearly every day, often multiple times so it doesn’t matter (I had only one longer fast in my life, in my high-carb times. it was easy due to pure determination and curiosity. I couldn’t do that now. I didn’t notice fat adaptation or ketosis helped much with fasting though my average eating window did diminish at some point). If you have enough fat reserves and feel good, a longer fast may be fine but I am not knowledgeable about it (I theoretically don’t even have enough extra fat for such a long fast without problems. but in practice, I can’t tell without seriously trying and maybe not even so). 72 hour fasts now and then should help enough with fat-loss and autophagy alike and they seem safer to me than longer ones. Some people tend to overdo fasts too.