"When mercy dries up, fasting suffers drought, for mercy is to fasting what rain is to the earth. The one who fast may prepare his heart, cleanse his flesh, pull out his vices and sow virtues. But if he does not sprinkle his plants with streams of mercy, he does not gather his harvest. O faster, when your mercy fasts, you field fasts, too." - Peter Chrysologus
I read in one of Archbishop Fulton Sheen's books that he never recommended fasting to anyone because he couldn't do it himself! He would get quite ill, so he tried to do other things to replace fasting.
I used to be able to fast standing on my head. I found it very easy. During one particular Lent I was having a very tough time. I could not get past one meal! It was awful! I felt terrible! I got weak and dizzy and my stomach churned for food! I finally gave up. The reason? I was pregnant with my daughter. But I have had a hard time fasting ever since.
So, I'll stick will Archbishop Sheen on this one.