If you want to see what happens when the writers lose their nerve and try to explain everything, watch Lost.
There really needs to be an "engineer plot" genre where plot stays consistent to a small set of made up axioms. "The Strain" made an attempt. It boggles the mind why not in a single one of the zombie stories out there nobody bothered to wonder where the zombies get the energy? The way most of them work it's like cold fusion landing in one's lap.
Zombies, like vampires in the pre-industrial age, are meant to represent the horrors that lurk beyond the limits of human understanding and control. Although I'm sure some author has attempted to "harden" zombies like that, to me the more you try to explain them, the less effective they are as monsters. Because they don't work rationally, they're demons of the Id.
(Also: Leslie Nielsen's first starring role).
You will enjoy the book "The Girl With All The Gifts"
Spoilers in link: https://en.m.wikipedia.org/wiki/The_Girl_with_All_the_Gifts
There is quite some overlap with fan fiction, because people like to "fix" non-rational fiction. Eliezer Yudkowsky and his take on Harry Potter is the prime example. I can also recommend Alexander Wales who also made original fiction.
Probably the oldest related work is A Connecticut Yankee in King Arthur's Court by Mark Twain.
Another name mentioned often in this genre is Brandon Sanderson and especially his Mistborn series, but I have not read it personally.
Text: https://www.fanfiction.net/s/10360716/1/The-Metropolitan-Man
Free audiobook: http://www.hpmorpodcast.com/?page_id=1705
From brains. Duh. ;)
Zombies are like that. They gorge on fatty foods, like brains, bone marrow, and body fat, then go into an induced stasis that outwardly resembles death.
The zombinism vector is undoubtedly an endoparasitic fungus related to Cordyceps. Mycelium spreads throughout the host during the infection, preferentially following existing neural pathways, and flooding the body with antibiotics, to kill native gut bacteria and other possible putrefying factors. The normal digestive functions are destroyed. The regular circulatory system is destroyed. The only elements preserved are sensory organs, muscles, skin, and bones. All other functions are replaced by the fungus. The mycelium, as it followed the existing neurons, actually grows into a replacement brain and nervous system as it destroys the host's nervous system.
The copy isn't perfect, though, and genetically hardcoded structures produce an instinctual desire to seek out and eat more fat. Destroying the head does not actually kill the fungus, but it does remove its ability to create a facsimile of a mammalian brain, by scrambling the template. It could still make the muscles twitch, but would have no means of coordinating them into coherent movements.
I would therefore expect a zombie running low on energy to have almost no fat left, and ascocarps growing out of it all over, like cactus spines. It would probably resemble a spiky mummy. Any rotting appearance would be due to colonies of microorganisms that have evolved resistance to the fungal antibiotics.
So it's not just eating brains, but also not spending as much energy as a human normally does while using the organs evolved to keep a human brain alive.
Which is exactly what I concluded.
Midichlorians