In my experience, sprintingsprinting while jumping around depletes the hunger bar more rapidly than anything else I do. This is confirmed by this Exhaustion Level chartthis Exhaustion Level chart taken from the wiki:
NOTE: Any action not listed here will not increase exhaustion level. For example, the player can travel several days by boat and the food bar will not decrease.
Food poisoning seems to work rather effectively as well, so chow down on all the Rotten FleshRotten Flesh and Raw ChickenRaw Chicken you can find for additional exhaustion while you sprint and jump around like a madman.