Best Answer:
According to an article on Livestrong.com, Japanese sweet potatoes and "American" sweet potatoes are similar, with Japanese sweet potatoes tasting sweeter. I found several articles that talk about the nutritional values and properties of both types of sweet potatoes. (Each of the articles from Livestrong.com also references the sources that they used to find the information, and the others are from the USDA [United States Department of Agriculture] and the University of California).
Japanese Sweet Potatoes:
http://www.livestrong.com/article/280268-japanese-sweet-potato-nutrition/
http://www.livestrong.com/article/537421-nutritional-values-of-japanese-sweet-potatoes/
American Sweet Potatoes:
http://www.livestrong.com/article/531975-nutritional-facts-analysis-for-sweet-potatoes/
http://www.fns.usda.gov/fdd/facts/hhpfacts/New_HHPFacts/Veges/HHFS_SWEET_POTATOES_FRESH_F160-F163_Final.pdf
http://ndb.nal.usda.gov/ndb/foods/show/3274
Other 'Sweet Potato Nutrition' articles:
http://www.livestrong.com/sweet-potato-nutrition-facts/
http://cemerced.ucdavis.edu/files/40457.pdf
http://snap.nal.usda.gov/resource-library/whats-available-winter/sweet-potatoes-and-yams
Jennifer, ipl2
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Source(s):
http://www.livestrong.com/article/280268-japanese-sweet-potato-nutrition/
http://www.livestrong.com/article/537421-nutritional-values-of-japanese-sweet-potatoes/
http://www.livestrong.com/article/531975-nutritional-facts-analysis-for-sweet-potatoes/
http://www.fns.usda.gov/fdd/facts/hhpfacts/New_HHPFacts/Veges/HHFS_SWEET_POTATOES_FRESH_F160-F163_Final.pdf
http://ndb.nal.usda.gov/ndb/foods/show/3274
http://www.livestrong.com/sweet-potato-nutrition-facts/
http://cemerced.ucdavis.edu/files/40457.pdf
http://snap.nal.usda.gov/resource-library/whats-available-winter/sweet-potatoes-and-yams