She refuses to eat humans and loses her ability to consume normal food, so how does Nezuko survive without eating?
Nezuko is able to survive without eating by sleeping instead. She uses long periods of sleep as a technique to heal her injuries and substitute the urge to eat human flesh.
Master Urokodaki explains this theory to Tanjiro before the boy heads out on his first mission. Nezuko secures herself inside a bamboo box designed by Urokodaki as well.
Urokodaki’s theory on how Nezuko can survive without eating
In chapter #10, Tanjiro prepares for his first demon slaying mission. Master Urokodaki details the Nichirin Sword, a weapon that changes color depending on the bearer. Each specific color has unique characteristics.
Urokodaki says that few slayers have black swords, making Tanjiro’s blade unique with an unrecorded history. He explains the Demon Slayer Corps outfit, made from a special fabric that breathes easily and can resist both flame and water.
The outfit can also repel the fangs and attacks of lesser demons.
Finally, Urokodaki gives Tanjiro a specially made box for Nezuko to fit in. Urokodaki says the box is made from an “incredibly light” wood named Kirikumo Cedar. The box is coated with Rock Lacquer to harden the exterior, proving strength above a normal box.
“This is mere speculation,” Urokodaki says. “But instead of eating the flesh of humans, Nezuko may sleep to replenish her strength.”
Nezuko almost breaks her vow to not eat humans a few times, but is able to pull herself together and sleep instead. Sleeping becomes a common technique for her throughout the series. Often, Nezuko will contribute to a fight and then sleep her injuries back to full strength before rejoining the brawl again. Nezuko was once able to sleep for 2 years.
So that’s the answer. Nezuko is able to survive without eating by substituting in sleep. She sleeps in order to heal her injuries and resists the urge to eat human flesh.