Tough questions. All I can tell you is, we are all different, all fasts are different.
I agree the human population has been eating poorly for a long time, since the industrialized world started making packaged foods. It will get worse because the new generation only sees that as food. Everyday I see very small children walking to school in the morning with skittles, fruit loops, gummy bears in their hands, well, who gave them that? An ignorant parent.
I had my share of junk food, with my own choice, when I was young, it took me many years of fasting to heal. I am still not totally healthy, I get small bumps in my health. I also don't eat any junk, eat fruits and vegetables which has been most beneficial to me.