The idea that Undead do not eat is a misconception.

It is true that lowly Skeletons and Ghosts do not feel hunger or possess a sense of taste. However, Zombies and Undead of a certain Rank and above feel hunger and have a sense of taste.

Of course, as the biological processes of Undead have stopped, they do not need to eat. They have no problems continuing to function even if they do not eat for years at a time.

However, they cannot escape the restrictions of having once been living creatures entirely. They still retain some of their primitive needs.

Out of the three main needs*, the need for sleep is the one that disappears entirely. Undead do not tire, so they do not need sleep. If they try to sleep they can reach a state similar to being asleep, but this is in carried out in order to recover from mental fatigue rather than physical, and is done more for self-satisfaction.

TLN*: As I mentioned in chapter 17, the three main needs are the need to eat, the need to sleep and the need to reproduce.
Interestingly, the need to reproduce remains. As the body has already died, there is no desire to leave offspring behind, but the deed is still physically possible. It is carried out by some to absorb spirit from the living and by those that died with a strong liking for engaging in intercourse.

And the need that remains in its entirety is hunger. This desire that remains in the souls of the Undead drives Zombies to eat the flesh of the living and drink their blood to absorb the Mana contained within and gain experience.

Skeletons and Spirit-type Undead can also increase their Rank to become superior versions of Undead, gain the【Spirit Form】skill to gain a replacement for flesh and consume the flesh and blood of the living or even absorb their Vitality in a more direct way.

The Undead Titans of Talosheim were no exception; they ate as much as they liked. Most of the food they had been eating was the flesh and blood of monsters brought into the city, but from time to time they also ate the surrounding grass, tree branches and rock fragments.