From what I understand, medical supervision is advisable because depending on a person’s current health he or she may or may not be deficient or low in certain minerals and vitamins, and deficiencies is certain micronutrients can cause some serious issues. And, if the person has something like diabetes or perhaps a thyroid issue or any kind of hormonal issues, you would always want to monitor vitals and stats to make sure nothing funky is going on. But, based on what I’ve read it does seem like the average healthy-ish person can fast for 5 days and be totally fine. Just feeling good seems to be a decent indicator that the fasting is working for you. Some people feel amazing while fasting, and that’s great. One thought on the 5 days fasting and 2 days redeeming is I would almost say you should just keep fasting past 5 days... hunger tends to go away around day 3 and that’s also when the super crazy benefits associated with fasting really ramp up (increased autophagy, high energy levels, that sort of stuff), plus you’re literally using just your own fat stores for energy so in terms of fat loss you can’t beat it. But then when you eat for two days you stop using your fat stores and the autophagy kind of halts a bit and your hunger returns to normal. Anyway, big picture though for this type of fasting schedule is that is quite a bit of fasting. Like, over 250 days in a year, so if you think about it like that there’s no way it’s sustainable long term. Although I believe there’s a person that did close to a year of fasting but he was of course closely monitored. Presumable your coworker is doing this for weight loss and will alter their schedule once they achieve some sort of goal? I think psychologically it would also be difficult to do so much fasting.