Organs during fasting

Answer

You’re conflating body fat with dietary fat. You don’t gain body fat by eating dietary fat. Most of the body fat we have probably comes from excessive carbohydrate intake.

Your brain is always the priority for energy expenditure. Your body prioritizes what it needs. If a bodybuilder (or anyone, for that matter) stopped consuming protein, their body would be unable to repair and replace damaged muscle mass, and it would atrophy.

Answer

1. te protective mechanism is called Human Growth Hormone, you can look it up, it spikes really high when you fast
2. your body prioritizes sugar as first fuel (even though fat is a more efficient fuel) so when you eat sugars while fasting, your body will have to deplete the sugars first before it continues to burn the fat