Is expired food healthy

No, that's why it is "Expired".

Normally manufactures will allow for a small tolerance in the expiration dates of food, for example if canned food expires on 29/10/2013 it would normally be safe to consume for about a month after that.

After that, all bets are off, food could be contaminated and give you severe food poisoning. Expiry dates are the manufactures method of avoiding liability of a person falls ill after eating very old food (that could be "off").