In the past I've had low blood sugar issues (started shaking and got splitting headache) because I forgot to eat for 24h or so and worked long hours, it wasn't a nice experience and I most certainly wouldn't want to repeat that on purpose by fasting. In addition to that, I often "bonk" on longer bike rides (don't eat sufficiently) and do intensive cardio exercise 6 hours a week. I have a BMI around 22 (used to be lower but hey, I'm not getting any younger..).

So do you think this is something anyone can/should engage in? How do you decide if your body can safely engage in multiday fasting like that?