You shouldn't be hurt. If they were right, then you should be hurt for being stupid, but that's not the case.
My little saying:
All of the opponents of fasting, except for perhaps a few, have never fasted themselves.
All of the proponents of fasting, save for a few, have all fasted themselves.
There is a tremendous wealth of literature (the Bible, sheldon, hazzard, et al) that proves the infinite value of fasting. Many well respected leaders have shown that fasting is beneficial (Jesus, Moses, most of the prophets and apostles, Ghandi, etc).
I would have simply turned the truth of the argument back on them. They are scared of fasting because they are ignorant and weak. They could never do it themselves because they are of incredibly weak character. Challenge them to go 3 days without food (of course you need to do at least that yourself first, 60 hours isn't much but it's a start). They will soon realize that you are the better person and after they see the great benefits fasting brings you, they will be even more envious and spiteful.