Organs during fasting

Does the body protect important organs like brain, skin and eyes when fasting and just burn normal fat stores?

If so, could an overweight person just drop all fat from their diet and be healthy until they run out of normal, subcutaneous and visceral fats (under 5% bodyfat) ?

Also with protein: could a bodybuilder just stop eating protein entirely and the body would consume the muscle for repair functions instead of protein from important organs – until it runs out of muscle and is severely underweight bmi?