I know of no restaurants that would charge you if you got food poisoning. But saying that when you ordered a colossal burger it went straight to your waistline isn't a good excuse not to pay. Don't go in if you don't want to pay.
The problem is, the food poisoning usually manifests after you've already paid and left the resturant.
Could one do a credit card charge-back if they get sick after eating out? (Too bad I pay using cash though, so I am SOL.)