Sweet potatoes: reduced cancer risk
Sweet potatoes come in a range of colours of which those with an orange flesh are exceptionally rich in betacarotene, an antioxidant carotenoid which your cells can convert into vitamin A (retinol) when needed. Just 100g of orange-fleshed sweet potato provides over 8500mcg of betacarotene, which is at least as good as new carrots. If you ever see the red or purple-fleshed versions for sale, grab them quick, too, as they are unusually rich in anthocyanins; one study found the antioxidant activity of purple/red sweet potatoes was more than three-fold higher than blueberries.
Sweet potatoes have a lower starch content than normal white potatoes and therefore have less impact on blood glucose levels, too, as assessed by their glycemic index and glycemic load (boiled sweet potato GI 44 / GL 11 versus boiled Maris Piper white potato GI 85, GL 25). As a result, sweet potatoes are a valuable medicinal food for treating diabetes in Kagawa, Japan, while the leaves are used as an antidiabetic remedy in Ghana.
Sweet potatoes are one of the richest dietary sources of oestrogen-like plant hormones classed as lignans. Like their close cousins, the isoflavones, these are present in an inactive form. When you eat them, certain bowel bacteria convert them to mammalian enterolignans (eg enterolactone and enterodiol) which have a weak, oestrogen-like action. By interacting with human oestrogen receptors, these enterolignans block access to the stronger human oestrogens which are associated with hormone-dependant cancers of the prostate and breast. Enteroligans also have anti-inflammatory and anti-cancer actions by reducing the proliferation of abnormal cells, and triggering their programmed cell death (apoptosis).
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