North Koreans are smaller than South Koreans due to collapse of Soviet Union thus trade with it that is misleadingly labeled as "aid" despite fact material trade was being done to fullfil each others need, it wasnt anywhere close as Cuba to be considered aid. Collapse of SU which NK heavily depended on lead to famine due to necesary materials for fertilizers couldt be aquired for food production.
Also we should not forget that USSR and other "communist" countries were under western embargo.