I finished the campaign first before attempting this.
Use mission select and activate the famine mode cheat code by pressing X at the mission select menu. Only activate this cheat alone as you will not unlock the Master of Fasting achievement if you activate other cheats besides Famine Mode.
You obtain the Famine cheat code collectible in Mission 10: Nekravol after the fifth encounter of the mission, it is near the second set of dual crusher traps.
You can not do mission select in Extra Life Mode.
The quickest level to do this on is Mission 8: Sentinel Prime on I'm too Young to Die difficulty (or any other difficulty of you choice), where you can pick up 2 extra lives along the way to the only fight of the mission, which is the boss battle against the "Gladiator". Use the Lock-On Mod Rockets and the Arbalest Mod Ballista to make quick work of him.
Should only take you 5 minutes to do.