Yes, you're technically burning through your body's food supply when you fast. While that has survival implications, that's not really the point. The average American overeats like crazy and is addicted to junk food. Fasting helps to break that addiction so that you're more likely to use your crisis food wisely and not feel hunger pangs. When I tell people that I comfortably fast for 4 or more days, they think it's crazy and they can't imagine it, but it's really not that hard. That tells me that people are liable to digging into their food too early on in a survival situation.

The truth is that while I am gradually burning body fat intentionally, I've still got weeks worth of fat on my and probably will when I decide to reduce my fasting back to eating one meal a day. I'd rather burn that fat and eat minimally for the first week or two of a crisis before digging into my reserves. Let's say I learn that the supply chain will be broken for longer than expected; I want to have food around so I can calmly address the issue without having to panic about where I'm going to get my next meal.

To put it simply, I don't think most people have the discipline to not pig out on their earthquake kit or their pantry if they're stuck at home during a pandemic. There's a bit of a caloric tradeoff in gaining that discipline, but I think it's worth it.