native to:
sweet potatoes: tropical regions of the Americas
yams: Asia
in season: fall
Although they serve the same purpose and are used interchangeably in recipes, sweet potatoes and yams are not, in fact, the same thing. However, just in case there was any threat of clarity on the matter, what the supermarkets describe as "Garnet" or "Jewel" yams are in fact orange-fleshed sweet potatoes. For actual yams, you'll probably have to go to an ethnic market. Both vegetables should be kept out of the fridge in a cool, dark, reasonably dry spot.
Sweet potatoes are slightly more nutritious, but both are good sources of fiber, potassium, copper, manganese, iron, vitamins C and B6, thiamine (B1), pantothenic acid and folates. They both have plenty of antioxidants and very low glycemic indices. Yams are somewhat lower in calories; they have more omega-3s and a unique blend of phytonutrients. Sweet potatoes are significantly higher in vitamin A and anti-inflammatories. Yams can actually worsen symptoms of inflammatory diseases such as IBS, arthritis, and gout, but are thought to help relieve PMS symptoms, while sweet potatoes have a less desirable ratio of omega-3 and omega-6 fats.
Yams are of the genus Dioscorea in the morning glory family and are larger and have a thicker skin. They are used in Chinese, Korean, and Japanese traditional medicine to speed healing of wounds. They may also help stabilize hormonal patterns and lower the risk of osteoporosis.
Sweet potatoes are Ipomoea batatas in the genus Convolvulaceae. Conventionally-grown ones can be treated with dyes or wax and should be peeled before eating, while the skins of organic sweet potatoes can be eaten. Boiling is actually a good way of preparing them, because it makes the beta-carotene and vitamin A more available and lowers their glycemic index (it ends up at about half that of a baked sweet potato). For the best beta-carotene absorption, eat your sweet potatoes with a bit of fat or oil (stir-frying is a good option here). People with oxalate concerns should be careful of sweet potatoes, although they're not as bad as leafy vegetables such as spinach.
Sweet potatoes can be eaten raw, but yams contain bitter, unhealthy proteins and must be peeled and cooked. One variety, Japanese yam (Dioscorea opposita) is traditionally soaked in a vinegar solution instead of cooking, which amounts to much the same thing.
Read more:
label-style nutrition information for cooked yam
label-style nutrition information for cooked sweet potato
yams at Nutrition and You
sweet potatoes at whfoods.com
sweet potatoes and yams at Fullcircle.com
sweet potatoes compared to white potatoes at Cleveland Clinic
and, just for fun, here's the classic modern epicLutefisk and yams
Check back tomorrow for my own bit of doggerel about this Thanksgiving favorite (or, if you're a poetry-lover, maybe not...).
Versión en español: this post is also available in Spanish
Esperanta traduko: this post is also available in Esperanto, because Dana is a language geek.
