During the World War II, there was an embargo on ships crossing the South China Sea. There was no rice import, an staple of the people. People planted root vegetables like sweet potato/kumara, tapioca and pumpkin as staple.
Dad said when you eat this day in and day out, withour any oil or salt, you soon get very tired of it.
The world has turned around. I like sweet potatoes , and sometimes I steam them on top of the rice.