longer than 2 or 3 day fasts are really not good for my sleep or mental health. i quit because consistently fasting lead to me to develop an eating disorder, but even after my first ~8 day water + vitamin (potassium and salt included) fast i fainted, was constantly dizzy and foggy and had the worst constant migraines of my life. i lost 10.3 pounds but the next week i gained 8 pounds back. i find it really hard to lose weight now because of the half-year of fasting i did and what it did to my metabolism…i occasionally do a 2 day fast or intermittent fasting still, but the way i lost weight was with changing habits and exercise. trust me lovely, if you have the self-discipline to not eat for a week, you have the self-discipline to go for a walk and eat a little less. unless it’s an emergency i wouldn’t recommend long-term fasting; it doesn’t work and it hurts your body.
I can’t speak to cycle because I have an IUD, but I have never experienced hair loss in extended fasts. I’ve done up to 14 days. I experience sleep disturbances in days 1 and 2 and general body aches, especially in my back, the rest of the first week. (I sleep on my stomach and usually have back pain so I have always attributed that to healing.) The second week is all mental game—boredom hunger and “oh well I’ve done enough, I should just stuff my face”.
I also have an IUD, and experienced spotting during a 29 day fast. I had tons of pains on my body, especially in my lower back/sacrum and abdominal pains. I was basically attached to a heating pad for the first 2 weeks! No hair loss. No negative health impacts to report, just a generally unpleasant experience, compared to all the success stories I found here and on YouTube.