This is not true at all. There's perhaps a preference toward fat but muscle wasting absolutely occurs during fasting, and often at a relatively significant rat

This is not true at all. There's perhaps a preference toward fat but muscle wasting absolutely occurs during fasting, and often at a relatively significant rate. If you were to "run out of fat" entirely, you'd simply die with fairly significant caloric reserves in the form of muscle. This is not what is observed.