In the wild fish will naturally go a week or more without food. It's completely healthy, in fact, many fishkeepers intentionally fast their fish once and a while to help regulate their digestive system.
The trick is not to feed for a couple days BEFORE you leave and then do a partial water change, if the fish don't eat, they produce less waste. That way, you don't get any toxic buildup when you are gone.
Make sure you change your water when you get back, and resume regular feeding.
Ive left my fish for 17 days before without incident.
Fish are cold blooded, so their metabolism will drop without food. They will be less active, so don't worry if they look lethargic when you get back. Give them some food and within a couple hours, they will be back to normal activity levels.
Don't use the feeder blocks. I've heard so many stories about people coming back to tanks of dead fish, or even that they can contain tuberculosis (I think it was angry platy who had this problem, if I recall).