Despite the terms sweet potato and yam often being used interchangeably, they are actually not even botanically related. Yams are almost exclusively grown in Africa and are more dry and starchy compared to a sweet potato. So how did these two vegetables become so intertwined?

There are two different varieties of sweet potatoes, firm and soft. When soft sweet potatoes were being cultivated in the Americas, African slaves began calling them yams because of their resemblance to their familiar native vegetable. The name caught on as a way to distinguish between the two types of sweet potatoes. Today, you are unlikely to find a true yam in the grocery store unless you are shopping in an international market.

This MNT Knowledge Center feature is part of a collection of articles on the health benefits of popular foods. It provides a nutritional breakdown of the sweet potatoes and an in-depth look at its possible health benefits, how to incorporate more sweet potatoes into your diet and any potential health risks of consuming sweet potatoes.

Nutritional breakdown of sweet potatoes

One medium sweet potato (2" diameter, 5" long, approximately 114 grams) provides 162 calories, 0 grams of fat, 37 grams of carbohydrate (including 6 grams of fiber and 12 grams of sugar), and 3.6 grams of protein according to theUSDA's national nutrient database.

Sweet potatoes pack a powerful nutritional punch. They have got over 400% of your daily needs for vitamin A in one medium spud, as well as loads of fiber and potassium.

One medium sweet potato will provide well over 100% of your daily needs for vitamin A, as well as 37% of vitamin C, 16% of vitamin B-6, 10% of pantothenic acid, 15% of potassium and 28% of manganese. You'll also find small amounts of calcium, iron, magnesium, phosphorus, zinc, vitamin E, thiamin, riboflavin and folate.

Sweet potatoes are a great source of beta-carotene, a powerful antioxidant known to give orange vegetables and fruits their vibrant color, which is converted to vitamin A in the body. Consuming foods rich in beta-carotene may reduce the risk of developing certain types of cancer, offer protection against asthma andheart disease and delay aging and body degeneration.

Keep the skin on! The color of sweet potato skin can vary from white to yellow, purple or brown but no matter what color it is, make sure you do not peel it off. A sweet potatoes skin contributes significant amounts of fiber, potassium and quercetin.

Possible health benefits of consuming sweet potatoes

Consuming fruits and vegetables of all kinds has long been associated with a reduced risk of many adverse health conditions. Many studies have suggested that increasing consumption of plant foods like sweet potatoes decreases the risk of obesity, diabetes, heart disease and overall mortality while promoting a healthy complexion, increased energy, and overall lower weight.

Diabetes

Sweet potatoes are considered low on the glycemic index scale, and recent research suggests they may reduce episodes of low blood sugar and insulin resistance in people with diabetes. The fiber in sweet potatoes makes a big difference too. Studies have shown that type 1 diabetics who consume high-fiber diets have lower blood glucose levels and type 2 diabetics may have improved blood sugar, lipids and insulin levels. One medium sweet potato provides about 6 grams of fiber (skin on).

The Dietary Guidelines for Americans recommends 21-25 grams of fiber per day for women and 30-38 grams per day for men, which most people do not reach.

Blood pressure

Maintaining a low sodium intake is essential to lowering blood pressure, however increasing potassium intake may be just as important. According to the National Health and Nutrition Examination Survey, fewer than 2% of US adults are meeting the daily 4,700 mg recommendation for potassium.³ One medium sweet potato provides about 542 milligrams.

Also of note, high potassium intake is associated with a 20% decreased risk of dying from all causes.⁷

Cancer

Among younger men, diets rich in beta-carotene may play a protective role against prostate cancer, according to a study conducted by the Harvard School of Public Health's Department of Nutrition.⁴ Beta-carotene has also been shown to have an inverse association with the development of colon cancer in the Japanese population.³

Digestion and regularity

Because of its high fiber content, sweet potatoes help to prevent constipation and promote regularity for a healthy digestive tract.

Fertility

For women of childbearing age, consuming more iron from plant sources appears to promote fertility, according Harvard Medical School's Harvard Health Publications. The vitamin A in sweet potatoes (consumed as beta-carotene then converted to vitamin A in the body) is also essential during pregnancy and lactation for hormone synthesis.

Immunity

Plant foods like sweet potatoes that are high in both vitamin C and beta-carotene offer an immunity boost from their powerful combination of nutrients.

Inflammation

Choline is a very important and versatile nutrient in sweet potatoes that helps with sleep, muscle movement, learning and memory. Choline also helps to maintain the structure of cellular membranes, aids in the transmission of nerve impulses, assists in the absorption of fat and reduces chronic inflammation.⁶

In a study published by the Journal of Medicinal Food, purple sweet potato extract was found to have positive anti-inflammatory and antilipogenic effects as well as free radical scavenging and reducing activity.

Vision

According to Duke ophthalmologist Jill Koury, MD, vitamin A deficiency causes the outer segments of the eye's photoreceptors to deteriorate, damaging normal vision. Correcting vitamin A deficiencies with foods high in beta-carotene will restore vision.⁵

Also of note, the antioxidant vitamins C and E in sweet potatoes have been shown to support eye health and prevent degenerative damage.

A higher intake of all fruits (3 or more servings per day) has also been shown to decrease the risk of and progression of age-related macular degeneration.

REFERENCE

1.     Everyday Mysteries, Fun Science Facts from the Library of Congress, 23 November 2012, Accessed 19 August 2014.

2.     Traditional Holiday Foods — Tell Clients They Still Can Enjoy the Foods They Love and Keep Their Meals Nutritious, Constance Brown-Riggs, MSEd, RD, CDE,CDN, Today’s Dietitian
, Vol. 14 No. 12 P. 20, Accessed 19 August 2014.

3.     Inverse associations between serum concentrations of zeaxanthin and other carotenoids and colorectal neoplasm in Japanese, Okuyama Y, Ozasa K, Oki K, Nishino H, Fujimoto S, Watanabe Y, Int J Clin Oncol, 5 February 2013, Abstract, Accessed 13 December 2013.

4.     Plasma and dietary carotenoids, and the risk of prostate cancer: a nested case-control study, Wu K, Erdman JW Jr, Schwartz SJ, Platz EA, Leitzmann M, Clinton SK, DeGroff V, Willett WC, Giovannucci. E. Cancer Epidemiol Biomarkers Prev, 13 February 2004, Abstract, Accessed 13 December 2013.

5.     Myth or Fact: Eating Carrots Improves Eyesight, DukeHealth.org, Accessed 13 December 2013.

6.     Choline, Nutrition 411, Last reviewed December 2008, Accessed 13 February 2014.

7.     Increasing Dietary Potassium - Find Out Why Most People Need to Consume More of This Mineral, Today's Dietitian Vol. 14 No. 12 P. 50, Accessed 13 February 2014.

8.     Anti-obesity and antioxidative effects of purple sweet potato extract in 3T3-L1 adipocytes in vitro, Ju JH, Yoon HS, Park HJ, Kim MY, Shin HK, Park KY, Yang JO, Sohn MS, Do MS. J Med Food, October 2011, Abstract, Accessed 19 August 2014.