What made me choose urine fasting as opposed to other kinds of fasting? Well, first of all, I'm not "urine fasting" this time. Urine fasting is urine and water. I don't find this effective - perhaps one's urine needs to be alkaline? Or maybe that's not it. Frankly, my experience so far with urine fasting and UT is that I am very keen on the idea - it's a great idea - like fruitarianism - but it is not effective, in my view, on any plane. Even "hormonally". When fasting, we do excrete acid wastes in our urine - there's no question about that. Our urine becomes very concentrated in these acid wastes (toxins) during a fast, as the body repairs and detoxes. Drinking this is unquestionably drinking these toxins we are trying to get rid of. Perhaps that's why I haven't found it to work. However, I am following a strict fast of water, urine, and a tiny bit of grass juice plus fulvic acid, so I will let you know if I need to change my opinion.

As for what made me choose the idea of urine fasting, you will find there's interesting internet claims for it, especially by someone calling himself "Amen Heaven", or it could be "Ahmen Heaven" - many of these claims are based on an antiquated book by John Armstrong which I have and do not recommend. The rest of it is heavily "rishi"-ish and not very trustworthy, but sunds quite lovely - once again, fab idea.
I apologize if this doesn't help - what's your interest in the urine part?