That's how a regular practice of Catholic fasting can be thought of as a form of prepping too. The Holy Ghost's gift of fortitude is in part for times like these.
Indeed. People who aren't used to fasting could break down into violence within a day or two of going without food.
On the other hand, perhaps the best form of prepping is to put on weight. If I were to put on an extra 200 pounds, I could probably go a year without eating.
That is in fact the body's own prepping system. AND, unless they want to cook you, carve you up, and eat you, they can't really take those preps away. Not that I would normally want to live like that.