It’s something you’ll never truly figure out and can’t really as your body is a constant state of maintenance. When my brother was rushed to the hospital with pneumonia, the next day he didn’t really grow a beard. Makes sense. When you’re at deaths door, maybe don’t worry about growing hair.

Your body is always managing resources.

Basically it’s going to take the energy needed from other maintenance items (hair, nails, skin, etc.) and devote them to blood manufacturing. It’s also going to cut your energy to save calories so you’ll feel pretty sluggish for a bit.

How we currently deal with calories is just wildly misleading.