> Also people who fast for a long time: How do you do that? I get super hangry and find it really a struggle past a certain point of not eating.
Different people have different responses to fasting.
It's always been very easy for me to fast by becoming "at peace" with the feeling of hunger for the first 2-3 days, and after that I don't even notice. But later in life something about my body changed and my response to fasting was much more severe and I was suddenly unable to fast for more than 1-2 days due to extremely strong urges to eat, irritability, etc. This happened for 2-3 attempted fasts around the age of 32. A year or two later, and fasting is suddenly "easy" for me again. To be clear, the first 2-3 days usually sucks regardless.
I suspect that I am generally very good at metabolizing fat. When I get blood tests while fasting, even if I haven't eaten anything at all in 7 days, my glucose is generally still well above the minimum of normal, even sometimes towards the high side. I suspect that if my blood sugar was low, I'd have much more difficulty. It does seem to take 2-3 days for my body to "switch" to metabolizing fat at a high enough rate to raise my blood sugar up.
I also suspect different people have very different reactions to low blood sugar.
Just as a note, for me one of the biggest determinants of a successful fast is control over my environment. If there are people in my home cooking great food every night at the same time, it's very hard. If I'm living alone and let my fridge get empty, it's much easier. I've also dealt with it by shifting my work hours to leave later and come home after my partner has finished dinner and cleaned up the kitchen. But this is orthogonal to the above issue.