As far as I understand they have a shortage of everything, including livestock, so they end up using human feces as compost. This becomes a disease vector and you end up with ground water and vegetables contaminated with all sorts of parasites. This is specially critical for children because intestinal worms effectively hijack what little nutrients they can eat, creating even more malnourishment. [0]
[0] https://www.reuters.com/article/us-northkorea-unicef-idUSKBN...