Sweet potatoes are not always orange-fleshed on the inside but can also be a spectacular purple colour. Sometimes it’s impossible to tell from the skin of sweet potato just how rich in purple tones its inside will be.
Some nutritional benefits from sweet potatoes simply may not be achievable unless you use steaming or boiling as your cooking method.
Recent studies show excellent preservation of sweet potato anthocyanins with steaming, and several studies comparing boiling to roasting have shown better blood sugar effects with boiling.
Botanically, this starch-rich tuber belongs to the family of Convolvulaceae, and named botanically as Ipomoea batatas.
Its calorie content mainly comes from starch, a complex carbohydrate. Sweet potato has higher amylose to the amylopectin ratio than potato.
Amylose raises the blood sugar levels slowly on comparison to simple sugars and therefore, recommended as a healthy food supplement even in diabetes.
Two key antioxidant enzymes in sweet potatoes are copper or zinc superoxide dismutase and catalase.
One study showed purple sweet potatoes to have more than three times the antioxidant activity than that of one type of blueberry.
Research has verified that sweet potato extract can increase blood levels of adiponectin, a protein hormone produced by your fat cells, to regulate the way your body metabolize insulin, and even lower insulin levels when needed.
Other polyphenols in purple sweet potatoes include cyanidins and peonidins, which studies indicate have strong counter effects on cancer cell growth.
Interestingly, these anti-cancer compounds are more concentrated in the sweet potato itself than the skin, and may also lower the dangers posed by heavy metals and oxygen radicals, including mercury, cadmium, and arsenic.