"Have to" in the quote below tells me that you must eat, sleep and drink water.
http://www.gamespot.com/xbox360/rpg/falloutnewvegas/show_msgs.php?topic_id=m-1-56752497&pid=959557
What can you tell us about the new hardcoe Mode?
hardcoe Mode can be turned on or off at any time, although if you want the hardcoe trophy, you have to turn it on when initially prompted and leave it that way all the way to the end of the game. When it’s on, players will have to eat, sleep, and drink water every day. In addition, ammo has weight, companions can die, Stimpaks heal over time, and damaged limbs can only be healed with a Doctor’s Bag.
While you can fast travel in hardcoe Mode, you can’t if the time it would take to get you there would result in the player dying from dehydration/exhaustion/starvation.