Despite doing many fasts, I had kidney pain after my last fast. I think I had it because I had overdone it, and I think fasting puts extra strain on your kidneys (but perhaps someone else could confirm this). This as part of the reason why I embarked on a healthy eating course instead, so I could reserve fasting for when I really needed it. I was only fasting for weight loss, and so far I am finding that eating / exercise is more effective. Hopefully if and when I next fast my kidney will be in better shape. Hope this helps.