Yams are a tuberous vegetable, also known as colic root, devil’s bones, or China root. They are members of the plant genus Dioscorea and are related to the lily. There are more than 600 species of yam, most of which are native to Africa. Yams are now cultivated in many parts of the world, including Africa, Asia, the Caribbean, and Latin America. The long tubers grow below ground, have a rough and scaly exterior, and can reach up to 5 feet long. Their flesh can be ivory, yellow, or purple. The yam plant above ground is a twining vine.
Here in the United States, yams are often confused with sweet potatoes. In standard US produce markets, you will not usually find true yams – though some varieties of sweet potato (most commonly the copper-colored sweet potatoes with orange flesh) are marketed under the name yam. But these small, tapered sweet potatoes are not yams. In fact, they are from an entirely different plant genus and are related to the morning glory. To find real yams, most people living in the US will have to go to a store specializing in African, Asian, or Latin American foods.
Nutritional Properties of Yams
Yams contain a fair amount of potassium. They also contain vitamin C, vitamin B6, and beta-carotene, but not in large amounts. Though yams are super starchy, they are relatively low-glycemic due, in part, to their fiber content. Yams do not have high protein content – they contain about 2% protein based on their fresh weight.
Traditional Uses of Yams
Yam roots are a traditional source of food for many in Africa, Asia, and beyond. Yams can be easily stored outdoors for months in the dry season if communities lack refrigeration. Yams can be boiled, roasted, or mixed into stews and curries.
One species of yam, Dioscorea villosa, is native to North America. It is commonly known as wild yam. The roots of wild yam have been used since the 18th century by traditional herbalists and midwives, most commonly to treat issues of the female reproductive system.
Traditional herbalists and midwives have used wild yam to treat uterine cramping, pelvic pain, ovarian spasms, and dysmenorrhea (painful periods). Wild yam has also been used to combat nausea common to early pregnancy. Midwives sometimes use wild yam to calm labor pain and to help with uterine pain postpartum. Wild yam is used to treat symptoms of menopause as well.
Phytochemical Properties of Yams
Yams contain a chemical called diosgenin, a steroid saponin which can be used in laboratories to create synthetic progesterone, estrogen, cortisone, and DHEA (dehydroepiandrosterone). Diosgenin has been studied for its health benefits. Yams also contain dioscorins, their major storage proteins. Dioscorics may have health benefits as well. Below, we’ll look at what science has to say about the health benefits of yams, and these two compounds in particular.
3 Benefits of Yams
1. Yams may improve female sex hormone levels post-menopause.
A 2005 clinical trial replaced the staple food (usually rice) of 22 healthy, postmenopausal women with yams in two of three meals per day for 30 days. A control group was fed sweet potatoes. Serum levels of estriol, sex hormone binding globulin (SHBG), and estradiol were measured before and after the trial in both groups. The hormone levels of the group eating sweet potatoes remained unchanged at the end of the trial, whereas the group eating yams showed increased levels of all three sex hormones. The authors concluded that eating yams two meals per day could improve the status of sex hormones in postmenopausal women, though further study is needed to understand the mechanism behind these hormonal changes.
2. Yam extract may improve cognitive function.
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A 2017 study looked at whether diosegin-rich yam extract affected cognitive function in 28 healthy volunteers. The participants took yam extract prepared in olive oil over the course of 12 weeks, and a control group was given a placebo. Participants were given the Japanese version of the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), an assessment to measure neurocognitive function before and after the trial. Those taking diosegin-rich yam extract significantly improved their score on the tests. The study suggested that cognitive function in healthy adults was enhanced by the yam extract.
3. Yams contain antioxidants.
A 2012 study looked at the health benefits of dioscorins, a soluble protein found in yams. The study indicated that dioscorins have antioxidant, antihypertensive, and immunomodulatory properties. However, the authors recommended more research to fully understand the bioactive mechanisms of dioscorin.
Supplements Versus Food
If you’re interested in supplementing with yam extract, consult with your healthcare provider first to be sure it’s right for you. Also, be aware that many of the wild yam creams available are made with added synthetic hormones and chemicals. Find a producer who uses organic or wild-harvested roots and no added chemicals or solvents.
In terms of eating yams, it’s safe to say that including yams as whole foods in your diet is a fine idea, and it may even come along with some health benefits — unless, of course, there’s some reason they disagree with you. Yams may be hard to find, but that could be part of the fun. There are some great recipes out there for a wide variety of yam curries from all over the world. Some even mix them with sweet potatoes!
Shona Curley lives and works in San Francisco. She is co-owner of the studio Hasti Pilates, and creator of the website www.redkitemeditations.com. Shona teaches meditation, bodywork and movement practices for healing Lyme disease, chronic illness and pain.
Wu WH, Liu LY, Chung CJ, Jou HJ, Wang TA. Estrogenic effect of yam ingestion in healthy postmenopausal women. J Am Coll Nutr. 2005;24(4):235-243. doi:10.1080/07315724.2005.10719470
Tohda C, Yang X, Matsui M, et al. Diosgenin-Rich Yam Extract Enhances Cognitive Function: A Placebo-Controlled, Randomized, Double-Blind, Crossover Study of Healthy Adults. Nutrients. 2017;9(10):1160. Published 2017 Oct 24. doi:10.3390/nu9101160
Lu YL, Chia CY, Liu YW, Hou WC. Biological activities and applications of dioscorins, the major tuber storage proteins of yam. J Tradit Complement Med. 2012;2(1):41-46. doi:10.1016/s2225-4110(16)30069-4