They are high in vitamins A, C, E and B6, also high in potassium, calcium, sodium, phosphorus, manganese, copper, iron and magnesium... not sure on all accounts how different from the American variety, but the Japanese ones have a bit more potassium, and the American ones have almost twice as much vitamin A.
The Japanese ones are much more dry and can't be cooked exactly as you would cook an American sweet potato, your probably wouldn't be able to bake them, more likely you would steam them.
Re: Japanese Sweet Potatoes?