Editor’s Note: Each month, HerbalEGram highlights a conventional food and briefly explores its history, traditional uses, nutritional profile, and modern medicinal research. We also feature a nutritious recipe for an easy-to-prepare dish with each article to encourage readers to experience the extensive benefits of these whole foods. With this series, we hope our readers will gain a new appreciation for the foods they see at the supermarket and frequently include in their diets.
The basic materials for this series were compiled by dietetic interns from Texas State University (TSU) in San Marcos and the University of Texas at Austin (UT) through the American Botanical Council’s (ABC’s) Dietetic Internship Program, led by ABC Education Coordinator Jenny Perez. We would like to acknowledge Jenny Perez, ABC Special Projects Director Gayle Engels, and ABC Chief Science Officer Stefan Gafner, PhD, for their contributions to this project.
By Hannah Baumana and Mikala Sessab
a HerbalGram Associate Editor
b ABC Dietetics Intern (TSU, 2013)
Overview
The sweet potato (Ipomoea batatas, Convolvulaceae) is a trailing, herbaceous perennial.1,2 It is indigenous to Central and South America and grows best in subtropical climates, spreading along the ground and producing oblong, tuberous roots. The flesh of the tuber comes in multiple colors: orange is the most common, but white, cream, yellow, pink, or deep purple varieties also exist. The sweet potato plant has heart-shaped leaves and produces beautiful white, pink, or purple flowers as the plant matures.
Taxonomic confusion can arise over the common name of “yam” that often is given to sweet potatoes in the market. Botanically speaking, true yams belong to the genus Dioscorea (family Dioscoreaceae) and are much less common in the United States.3 In general, foods marked as “yam” in the United States should be
 assumed to be sweet potatoes. For reference, the common potato is Solanum tuberosum (Solanaceae), and belongs to a third distinct plant family than both sweet potatoes and yams.
Currently, sweet potatoes are produced in more than 100 countries. Domestication of the plant has led to its wide cultivation throughout Mexico, Central America, and the Caribbean. China now produces the most sweet potatoes, followed by Africa, Central America, South America, and the United States.4 The sweet potato tubers as well as the young leaves from the vines are consumed as food.1,2 While the tubers are in season in November and December, sweet potatoes generally can be found year-round in supermarkets.
Phytochemicals and Constituents
The sweet potato tuber is a nutrient-dense food that provides a high amount of beta-carotene, which is converted to vitamin A in the body.5,6 Vitamin A plays a vital role in developing and maintaining healthy vision. In addition, sweet potatoes contain the minerals potassium, calcium, iron, magnesium, zinc, and phosphorous. They are rich in dietary fiber and complex carbohydrates. Orange-fleshed sweet potatoes contain the highest levels of beta-carotene, while purple-fleshed sweet potatoes provide valuable anthocyanins, which are the antioxidant compounds that give berries and other foods their red, blue, and purple hues.
Sweet potato leaves and tubers are a good source of vitamin B6, which supports the prevention of cardiovascular disease by protecting the blood vessels and arteries. The human body cannot synthesize B vitamins, and they must be obtained from external sources via the diet.
Because of its nutrient density, sweet potatoes are incorporated into child malnutrition programs in developing countries, and agricultural scientists are working to improve the nutritional content of sweet potatoes even further.7 Chronic malnutrition afflicts 25% of all children under five years old worldwide.
The antioxidant and phenolic compounds present in sweet potatoes provide additional health benefits. Chlorogenic, isochlorogenic, and caffeic acids have antioxidant properties and mild blood pressure-lowering effects.8 Caffeic acid in particular shows immunomodulatory, antimicrobial, and anti-inflammatory activities.9 When coupled with the intake of protein, the antioxidants from sweet potato are more bioavailable.
The sweet potato leaves contain anthocyanins, phytosterols, essential amino acids, flavonoids, caffeic acid, and alpha-linolenic acid.5,6,10
Historical and Commercial Uses
Sweet potatoes are one of the oldest domesticated crops, with evidence of their consumption dating back 10,000 years, according to findings in prehistoric Peruvian caves.3 European colonizers brought sweet potatoes to Europe from Central and South America in the 15th century, and cultivation spread to Africa, India, southern Asia, and Indonesia by the 16th century. Due to African slavery and European colonization in North America, sweet potatoes became a cultural food staple in the southern United States. Sweet potato tubers and vines are used around the world as livestock fodder, especially in Asia.
In certain places where sweet potatoes are endemic, such as the Amazonian region, both the leaves and
 the tubers are used in folk medicine for their tonic properties, and for an array of conditions including tumors in the mouth or throat, stomach-related issues like diarrhea and nausea, fever, asthma, and burns.3,11 The vines and leaves of the sweet potato plant have reported uses as an aphrodisiac and laxative, and they were used to treat diabetes, uterine bleeding, mastitis, burns and abscesses, and sprains.3,10,12
According to traditional Chinese medicine (TCM) practice, sweet potatoes are said to benefit dry and inflammatory conditions in the body and strengthen the spleen and pancreas.10 In TCM, each organ of the body is “in charge” of specific wellness functions; therefore, by strengthening the spleen and pancreas, sweet potatoes help support healthy digestion, weight, and blood production.13 The tuber has been used as a galactagogue to increase a nursing mother’s milk supply. Based on traditional use, Taiwanese immigrants in the United States are growing sweet potato vines in their home gardens as a remedy for indigestion, as an astringent, and as a treatment to reportedly rid the body of toxins.14 Phytochelatins (glutathione oligomers) within sweet potato bind to heavy metals in the body in a process called chelation, which can serve to remove small amounts of heavy metals ingested in the food supply from the body. Currently, sweet potato tubers are still used in situations involving constipation or stomach and intestinal bleeding.
Modern Research
Sweet potato leaf (SPL) is being explored for its role in disease prevention due to its high levels of bioactive compounds, especially antioxidants. Possible applications include prevention of cardiovascular disease, type 2 diabetes, certain cancers, and immune-compromising conditions.6,15 A recent study showed that just 200 grams of the purple-tinged leaves consumed over a period of 14 days reduced the oxidation of LDL cholesterol particles, which is the basis of arterial plaque formation.
The caffeic acid, anthocyanoside, flavonoid, and arabinogalactan-protein contents of SPL make it a possible antidiabetic food. In an in vitro study conducted to evaluate the ability of purple SPL to increase glucose uptake, the extracts showed varying degrees of antihyperglycemic activity, which the researchers attributed to the quercetin content of the leaves.12 In addition, the relative glycemic load of the sweet potato tuber is lower than that of the common potato, making sweet potato a healthy choice for diabetic patients.16 The glycemic load is calculated from a food’s glycemic index, a value assigned to foods based on how slowly or quickly their ingestion causes increases in blood glucose (blood sugar) levels.17 Foods with a low glycemic index release glucose slowly, which is generally desirable for glucose control, while foods with a high glycemic index are preferable for hypoglycemic (low blood sugar) conditions.
Polyphenol-rich SPL extracts have also shown antitumor effects. A study in mice showed that oral administration of a fractionated SPL extract for six weeks inhibited growth and progression of prostate cancer cells, inducing apoptosis (a pre-programmed “cell suicide” that halts the spread of cancerous cells) and decreasing tumor volume.18 Researchers observed no further toxicity from the administration of the extract. Sweet potato peels, which are usually discarded as waste, also contain beneficial amounts of antioxidants, and an in vitro study using an alcoholic extract of the peels showed cytotoxic activities against breast, colon, ovary, and lung cancer cells.19
The purple tuber, which contains higher levels of antioxidant anthocyanins and anthocyanidins in comparison to the orange-fleshed variety, has been investigated for its anti-inflammatory and cytotoxic properties. In a simulation of a superficial wound, an extract of a Taiwanese varietal of purple sweet potato was found to promote wound-healing and supported the repair process.20 In the same study, an in vitro investigation showed that the extract induced apoptosis of breast, gastric, and colon cancer cell lines.
Nutrient Profile21
Macronutrient Profile: (Per 1 cup raw sweet potato, cubed [approx. 133 g])
114 calories
2.1 g protein
26.8 g carbohydrate
0.1 g fat
Secondary Metabolites: (Per 1 cup raw sweet potato, cubed [approx. 133 g])
Excellent source of:
Vitamin A: 18,869 IU (377.4% DV)
Very good source of:
Manganese: 0.34 mg (17% DV)
Dietary Fiber: 4 g (16% DV)
Vitamin B6: 0.28 mg (14% DV)
Potassium: 448 mg (12.8% DV)
Good source of:
Magnesium: 33 mg (8.25% DV)
Thiamin: 0.1 mg (6.67% DV)
Phosphorus: 63 mg (6.3% DV)
Vitamin C: 3.2 mg (5.3% DV)
Also provides:
Riboflavin: 0.08 mg (4.7% DV)
Iron: 0.81 mg (4.5%DV)
Calcium: 40 mg (4% DV)
Folate: 15 mcg (3.75% DV)
Niacin: 0.74 mg (3.7% DV)
Vitamin K: 2.4 mcg (3% DV)
Vitamin E: 0.35 mg (2.3% DV)
DV = Daily Value as established by the US Food and Drug Administration, based on a 2,000-calorie diet.
Recipe: Healthy Loaded Baked Sweet Potatoes
Courtesy of North Carolina Sweet Potato Commission22
Ingredients:
Directions:
References
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Tuesday, 20 December 2016
Food as Medicine: Sweet Potato (Ipomoea batatas, Convolvulaceae)
