Nuanced issue. I recommend listening to Peter Attia's podcast episodes (and potentially reading his book Outlive) about this. In short, it can be useful for metabolic health for some people but you must balance altering metabolism and losing muscle mass with prolonged fasting. Intermittent fasting hasn't been shown to be better for weight loss but some people do find success so its an individualized story (rather than a one size fits all). Intermittent fasting (e.g., 16 hour fast, 8 hour eat) can be a great primer to doing a longer fast. In my experience, meditation (and intermittent fasting leading up to) was quite helpful in setting the stage and drinking salt water during a 72 hour (prolonged) fast makes it much easier. Apparently, weight training during long fasts can help minimize muscle breakdown. I think its a great experience to try this at least once to see how interesting the mindfulness experience (and gut rest) can be. Thin people (or those nearing and after age 50) should approach this with a nuanced approach so as to not lose muscle mass. Also, refeeding after 60 to 72 hours isn't necessarily harmful but can be associated with watery stool urgency for a couple hours after refeed so you want to be somewhere safe when breaking a long fast. I've gone from doing it once a month to maybe once or twice a year now bc my main goal is avoiding loss of muscle mass and avoidance of deranging my metabolism. Don't be dogmatic. It's good to experiment but develop a nuanced strategy for fasting rather than doing it because everyone else is doing it.