I say it again, some people don't seem to read previous input.
When you start you are probably dehydrated and haven't eaten for dayz!
"I ate and drank til i got the message "Your stomach feels completely full", then i was able to run around for 2 hours without drinking or eating (the amounts might need adjustment). Also, just because the icons in the inventory is gone, doesn't mean you are filled to the top. Those icons just show when you are on critical levels."