A yam is not, contrary to belief in the US and UK, a sweet potato. The two tubers are in fact unrelated species, with the yam tasting more like the common potato than the sweet potato, Ipomoea batatas. The yam is more closely related to Dioscorea deltoides. It is also known as the cinnamon vine and the Chinese yam, but there are more than 200 varieties grown. Dioscorea esculenta is the one that grows in India (a sweet yam) and the wild yam is Dioscorea villosa. They are related to the common black bryony in Britain, but the root of this plant is reputed to be poisonous.
   Yams may have flesh which is white, ivory, yellow or purple, (but not orange) and have skin which is white, pink or browny-black. It is starchy and could be either creamy or firm when cooked depending on which variety you buy. They can weigh anywhere between 4 and 10 lbs, so are hefty types of tuber.
   The name yam comes from African words such as “nyami” which is what the tuber is called by some who live in that continent. Both yams and sweet potatoes contain vitamin B6 which breaks down homocystine which damages blood vessel walls. Some people have heart attacks because they have high levels of this in their bodies, and as it is known that vitamin B6 reduces the risk of heart disease, a yam could be the preventative you have been looking for. They have white flesh (on the whole) and taste earthy, although there are some sweeter varieties. The tuber is also rich in potassium which lowers blood pressure too. Yams contain dioscorin, a storage protein which may also reduce blood pressure. They also contain steroidal saponins one group of which is disogenin which may help to reduce the risk of osteoporosis. Chinese researchers in 2001 concluded that dioscorin “may play a role as antioxidant in tubers and may be beneficial for health when people take it as a food additive or consume yam tubers.” Later research in 2009 showed that it had immunomodulatory effects and can boost the workings of the immune system.
  In traditional Chinese herbal medicine it is believed that yams can affect the body’s organs and support their functions. They are also given to promote lactation in breast-feeding mothers.
  Research is currently being carried out into the B-complex vitamins and their properties and it is thought that vitamin B6 may help with PMS/PMT as well as in the menopause. Yams could be a natural alternative to hormone replacement therapy (HRT).
  Yams contain many minerals including calcium, chloride, copper, iron, magnesium, manganese, phosphorus, potassium, selenium and zinc. They are rich in dietary fibre so good to prevent piles and to cleanse the bowels. Apart from the B-complex vitamins they also contain vitamins C, E and K, and 18 amino acids.
  Yams are best baked or roasted and can be used as the common potato.

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