Okinawan sweet potatoes are even sweeter than regular sweet potatoes. The antioxidant anthocyanin causes Okinawa sweet potatoes’ beautiful, deep purple color, the same antioxidant found in blueberries, a fruit often praised for its high levels of antioxidants. However, Okinawa sweet potatoes contain 150% more antioxidants than blueberries, which makes them a powerful cancer-fighting superfood.