This comment by wateronly about a 49-day fast being possibly TOO long agrees with my own experience of a recent 22-day fast. I was not overweight when I started and my goal was not to lose weight but rather to give up a dependence on caffeine and improve some medical conditions (only partly successful). After 22 days my weight had dropped to 108 lbs (BMI 17.4) for an average loss of 1.1 lb/day. This final weight was ten pounds below my desired target weight of 118 lbs (BMI 19.0). I was not bedridden after three weeks like wateronly for the last four weeks of a seven week fast. In fact I never felt lightheaded but I was becoming weak, bored and depressed. In spite of what has been said about protein sparing, there was muscle wastage and loss of vitality which is only slowly returning. I think that if I had pushed too hard I might have done some damage. Measured metabolic levels such as eGFR, creatinine and bilirubin were beginning to show signs of stress on the liver and kidneys. Urine pH was very acidic (5.5) for the duration of the fast. I have concluded that three weeks is about the limit for an unsupervised fast. If the goal is to reduce a lot of excess weight, more than about twenty pounds, I would prefer the alternate method of hiking from Mexico to Canada as I did twice. I lost fifty pounds of fat on my first border-to-border quest and have managed to keep it off ever since by daily exercise and caloric restraint.