How long are you going to be gone? I have left fish up to 14 days without food (the right conditions were used).
I would not go that long again, but I would not have a problem leaving them for up to a week unfed. For a few weeks before hand, start beefing them up with nutritionally packed food. About a week out reduce to normal feedings with daily water changes. 2-3 days before you go, feed as much as they will eat for each feeding, skipping the last day to clear our their systems. As close as possible before leaving, do a large water change.
When you return, feed them the same nutritionally sound food after another good water change. A few days of good feeding and they will be back to normal.