Fasting gurus, dietitians, and other knowledgeable specialists, please explain this to me.

It is a well established knowledge that after prolonged fasting, you don't immediately eat food, you slowly introduce it during many days, starting with carrot juices and then adding more 'light' foods.

I just finished my 21-day fast and ate the 'heaviest' food and ate a lot of it. And I feel good. No discomfort at all.