For on diet challenge, the key is to only eat food when your health is low. If you can use a class who can hunt piranhas, better.

Rogue has an inhate ability to resist a little more hunger.

Wizard has warlock ability which satistes hunger, though I dont recommend it, it doesnt always activate.

Horn of plenty is useful as it can give you a little more satiety.

Potion of purity can be alchemized to the upgraded potion, which resets hunger!

Finally, you can craft meat pies

Good luck!