I was very skinny, but somehow still had fat. Sometimes I bought pants from the women's section or I would take pants to my mom to sew the waist tighter, because I was so thin I couldn't find clothes that fit me (I have some pictures of me wearing my 108lb girlfriend's pants stashed somewhere). I exercised a bit but seeing me without a shirt you could tell I had manboobs and a tiny-lil bit of a potbelly and no abs at all, not even the skinny ones.
At some point I developed fainting on sight of blood. I would brush my teeth, and if I scratched my gum and blood came out -- I had to run to the bed asap before passing out. To this day I don't know if I was just afraid of blood (blood doesn't affect me anymore), or I had gotten so weak I was actually nearing total collapse. Blood tests were surprisingly fine I just had low iron.
Looking at that period back, I 'm trying to see if the advertised benefits applied to me. I didn't get sick much, but I don't get sick in general. Aging... well what can you say to an 18-22 year old about aging. My libido was low which makes sense I guess. Energy, regular levels. I don't know, I was just a very thin dude, fasting or not, no major epiphanies or amazement. I suppose it's amazing that one can survive fine, no suffering, going for so long without food, but it wasn't better than eating.
I am very surprised at how people swear by it. Maybe life is much worse when you eat 3 meals per day? I don't know, nowadays (early 30s) I eat 2 meals and exercise a lot and I 'm pretty content. I think for me, exercise did the trick that elevated both my mood and my energy levels.
Would I do the crazy 5-day 4 year fast again? If I was young and "hungry" sure, but it's definitely miserable. Food can be a great social thing to do with friends, and a cool experience especially when trying new dishes and restaurants. The huge food diversity in SF spoiled me.
Edit: back then I was very ashamed of my fasting and try to hide it from friends etc. A few weeks ago I was shocked when a coworker told me he was doing a 7 day water-only fast. We 've come a long way!