I'm almost 60, and a few years ago I started fasting with water only for 7 days twice/year, plenty of energy, and great brain stimulant. I have tea, coffee, vitamins, veggie water (for potassium) and resveratrol (200mg) it really makes me feel brilliant, with perfect eyesight, and less fat. It makes me feel younger, Its as if I can feel those old slow cells getting barbacued and turned into protein, and I can feel the insulin "police" open the barrier to convert fat into glucose drip by drip, all day long. Not even a grain of hunger because I have that constant blood sugar level. If I feel a bit weak, (not often) I simply do some squats, that tells the body, "this man is serious, give him some sugar" so I can honestly say that I never feel hungry.
BUT now I've been reading about RESISTANT FAT and it seems (with rats) that fasting makes you retain fat, which is logical. I found that myself, after fasting I find it almost impossible to lose internal belly fat (pot belly, protruding) So I've stopped fasting now, and prefer to eat smaller meals (tapas)