One thery for the issue with HFSC(?HFCS) is they reduce the body's ability to measure how many calories it has consumed which promotes over eating. The other problem is they tend to be in high calory low nutrition food so people need to still need to eat nutrent food and the "empty callories" don't really help.

PS: While I have never heard much mention of this, I suspect people crave food that contain nutrents they are missing. So hunger is probably a fiarly complex system that might not be all that robust to "new" food types.