Just a couple hours shy of thirty days, a few years ago. I try to do a minimum of a week every year now. I did not do it for weight loss, but to restore health. 21 days is thought to be the ultimate reset button, but once I got there I still felt good and had a lot of healing happening, so I waited until I experienced what is called "true hunger." It's a sensation that is impossible to resist, and you don't feel it in your stomach. It's like the roof of your mouth and the throat demands food. Fasting corrected bone issues, migraines, put Lyme into remission for a good period, scars drastically reduced and improved range of motion in a joint, and most importantly I stopped getting sick. I was sick back to back for months when I finally decided to try to fast. Can't say enough good things about fasting. It's a lost form of self care for most of the population.