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Sweet Potato

Scientific Name(s): Ipomoea batatas L.
Common Name(s): Caiapo, Camote, Kumara, Nyamis, Sweet potato, Yam

Clinical Overview

Use

Limited clinical studies of sweet potato use in type 2 diabetes, vitamin A deficiencies, or for its antioxidant, cardiovascular, and immune effects have been conducted; information is lacking to recommend sweet potato for any use.

Dosing

Diabetes: 4 g/day of a sweet potato preparation (caiapo tablets) given for 3 to 5 months has been used in clinical studies. Clinical studies evaluating efficacy of the nutraceutical caiapo used 2 g (low dose) or 4 g (high dose) daily, for a total of 4 tablets daily (each containing either 168 or 336 mg of powdered white-skinned sweet potato). Sweet potato supplements are available in powder and tablet (caiapo) forms. Dosage regimens vary, but most commercial manufacturers suggest 2 tablets 30 minutes before meals, up to a total of 6 tablets daily. Vitamin A deficiency: Daily consumption of beta-carotene–rich sweet potato (orange-fleshed varieties) has been used to improve vitamin A status.

Contraindications

Hypersensitivity to any of the chemical components of the plant species.

Pregnancy/Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking. Women with hypersensitivity reactions to the plant should avoid use.

Interactions

None well documented.

Adverse Reactions

Historical and clinical data report no serious adverse reactions. Patients with known hypersensitivity reactions to the plant may develop generalized urticaria, hypotension, and edema of the hands and face. Dizziness, loss of consciousness, nausea, vomiting, and a sensation of tickling and tightness in the throat have been documented.

Toxicology

No data.

Botany

The sweet potato plant is an herbaceous perennial vine that originated in Central America. Although China is considered the leading producer of sweet potatoes, the plant is widely cultivated and consumed throughout the world. It has alternate, heart-shaped, lobed leaves and medium-sized flowers. The root is edible and is often long and tapered. The skin may be red, purple, or brown and white. The interior, or "flesh," may be white, yellow, orange, or purple. The leaves and shoots are sometimes eaten as greens. Synonyms include Convolvulus tiliaceus auct. non Willd.; Ipomoea fastigiata (Roxb.) Sweet; Ipomoea tiliacea auct. non (Willd.) Choisy; Ipomoea triloba auct. non L.1, 2

History

Sweet potato is one of the world's largest food crops and is important for the growing populations in Asian and African countries. The plant has been used medicinally in Japan for treating diabetes and other diseases. American Indians used sweet potato to treat thirst and weight loss attributed to diabetes.3, 4, 5, 6

Chemistry

Numerous extensive phytochemical investigations focusing on the nutraceutical properties and physiological functions of sweet potato have been conducted.7, 8 The root and skin contain most of the studied medicinal components. High levels of polyphenols, such as anthocyanins and phenolic acids (eg, caffeic acid), have been isolated from sweet potato. Chlorogenic, dicaffeoylquinic, and tricaffeoylquinic acids are derivatives of caffeoylquinic acid that protect the root from fungal diseases and have potential cancer chemoprotective effects. The numerous acylated anthocyanins are the major color constituents in the storage roots and play a major role in the plant's antidiabetic properties. Sesquiterpenoids include 6-myoporol and ipomeamarone. Structural properties of the anthocyanins important for bioactivity include phenolic esters of the sugar, 2 hydroxyl groups on the aromatic ring, and an unsaturated alkyl chain in the acylated moiety.5, 9, 10, 11, 12

The plant's antioxidant activity is associated with its alpha-tocopherol content, alpha-tocopherol being the most common form of vitamin E and comprising 25 mg per 100 g of sweet potato shoots. The 2 storage proteins sporamins A and B account for more than 80% of the total protein isolated from the roots of sweet potato.13, 14

Uses and Pharmacology

Antioxidant effects

Animal and in vitro data

The major phenolic components in a 70% methanol extract of sweet potato showed strong antioxidant activity in a linoleic acid–aqueous system.15

Anthocyanins of purple sweet potato have antioxidant activity. Levels of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity were increased in collected urine samples of purple sweet potato anthocyanin–injected rats and in 6 human volunteers administered a purple sweet potato beverage. The degree of radical scavenging activity for some of the anthocyanins was higher than that for ascorbic acid.16

Clinical data

A clinical trial reported modulation of antioxidative status and decreased exercise-induced oxidative damage in healthy young males (N=15) following 7 days of purple sweet potato leaf consumption after completing a running exercise protocol.17

The bioavailability of polyphenols in purple sweet potato leaves was demonstrated in a clinical study, with reported potential for enhanced antioxidant defense and decreased oxidative stress in young healthy adults.18

Cardiovascular effects

Animal data

A sweet potato leaf extract was examined for relaxant activity in isolated rat vascular aortic preparations. Sweet potato showed 97% relaxation activity for endothelium-intact aortic ring preparations but only 35% in the mesenteric vascular bed. The vasorelaxation mechanism of action was similar to that of the pharmacological agent acetylcholine.19

Clinical data

Research reveals no clinical data regarding the use of I. batatas in cardiovascular disease; however, a sweet potato/footbath/acupressure massage intervention to prevent constipation was conducted among hospitalized patients with acute coronary syndromes.20

Diabetes

Animal data

Blood glucose-lowering activities of sweet potato have been demonstrated in animal studies.8

In a free-glucosidase (AGH) assay system, potent AGH inhibitory activity was observed with anthocyanin extracts from the storage roots of purple sweet potato (50% inhibitory concentration [IC50]=0.36 mg/mL). The extracts also inhibited alpha-amylase activity, indicating a potential role in suppressing the increase in postprandial glucose levels.21

The antidiabetic activity of white-skinned sweet potato versus troglitazine was examined in Zucker fatty rats over 8 weeks. Oral dosing of white-skinned sweet potato reduced hyperinsulinemia 23%, 26%, 60%, and 50%, at 3, 4, 6, and 8 weeks, respectively. White-skinned sweet potato also inhibited increases in blood sugar levels after administration of a glucose challenge test during week 7. Histology of the pancreas showed regranulation of pancreatic islet B cells. Isolation and purification of the antidiabetic component in white-skinned sweet potato was unsuccessful.3, 22

A sweet potato leaf extract given for 5 weeks decreased glucose levels in mice with type 2 diabetes; additional studies demonstrated stimulated secretion of glucagon-like peptide-1, resulting in increased insulin secretion.23

Evidence and similar experiments in rats indicate that acylated anthocyanins (eg, caffeoylsophorose) are responsible for alpha-glucosidase inhibitory activities of the extract. The production of adiponectin, a protein produced and secreted only from adipose tissue as a cytokine and found in human plasma, by transgenic sweet potatoes has gained pharmaceutical interest. Low levels of this cytokine or protein are associated with type 2 diabetes mellitus, obesity, and hypertension.11, 24

Clinical data

A Cochrane review evaluated randomized clinical trials comparing sweet potato with a placebo or a comparator intervention in type 2 diabetes. In 2 of the included trials (N=122), administration of sweet potato (caiapo tablets) produced significant improvement in glycosylated hemoglobin A1c at 3 to 5 months compared with placebo (mean difference, −0.3% [95% confidence interval, −0.6 to −0.04]; P=0.02). Included trials were all conducted by the same group of researchers.8

Immune system effects

Animal data

Sweet potato fiber, in combination with other therapeutic agents, may be useful in skin wound therapy. The healing effect of sweet potato fiber was evaluated for burns or decubital wounds in rats over 19 days. Outcome measures included reduction in size and changes in quality of the wounds. In rats treated with the sweet potato fiber covering, wound areas were reduced by 21% at day 9, 19.5% at day 11, and 18.7% at day 13 compared with controls. Healing times for both groups were 19 days for treated rats and 21 days for controls.25

In a mouse model, purified sweet potato polysaccharide (PSPP) isolated from the roots acted as a biological response modifier. In mice treated with PSPP (50, 150, and 250 mg/kg body weight for 7 days), phagocytic function, hemolytic activity, and serum immunoglobulin concentration increased in a dose-dependent manner.2

Clinical data

A randomized, crossover study involving 16 healthy, nonsmoking adults (7 men and 9 women) examined the effects of physiological doses of purple sweet potato leaves over 6 weeks. During week 1, control and experimental groups were subjected to a low-polyphenol diet. During weeks 2 and 3, the experimental group consumed a diet consisting of 200 g daily of purple sweet potato leaves, and the control group consumed a diet consisting of low polyphenols and carotenoids adjusted to the same level as those of purple sweet potato leaves. A washout diet followed during week 4. During weeks 5 and 6, the experimental and control groups switched diets. Results from blood and urine samples indicate that dietary intervention in the form of purple sweet potato leaf consumption modulated various aspects of immune function, including increased proliferation responsiveness of peripheral blood mononuclear cells, secretion of cytokines IL-2 and IL-4, and lytic activity of natural killer cells.26 Similarly, a clinical trial in healthy young males (N=15) reported decreased proinflammatory cytokine secretion after 7 days of consuming purple sweet potato leaves after completing a running exercise protocol.17

Immune system effects have also been documented for white-skinned sweet potato.27

Other uses

Chemoprotective effects may be associated with the anthocyanins and phenolic acids in sweet potato. Intake of an anthocyanin-rich purple sweet potato beverage improved serum hepatic biomarkers in Japanese men with borderline hepatitis who were otherwise healthy.28

Clinical studies document use of sweet potato, due to its provitamin A (or beta-carotene) content, as a potential long-term, food-based strategy to improve vitamin A deficiency in children in many developing countries.29, 30, 31, 32, 33, 34

Dosing

Diabetes

4 g/day of a sweet potato preparation (caiapo tablets) given for 3 to 5 months has been used in clinical studies.8

Clinical studies regarding efficacy of the nutraceutical caiapo used 2 g (low dose) or 4 g (high dose) daily, for a total of 4 tablets daily (each containing either 168 or 336 mg of powdered white-skinned sweet potato). Sweet potato supplements are available in powder and tablet (caiapo) forms.6, 35 Dosage regimens vary, but most commercial manufacturers suggest 2 tablets 30 minutes before meals, up to a total of 6 tablets daily.

Vitamin A deficiency

Daily consumption of beta-carotene–rich sweet potato (orange-fleshed varieties) has been used to improve vitamin A status.31, 32, 33, 34

Pregnancy / Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking. Women with a history of hypersensitivity reactions to the plant should avoid use.36

Interactions

None well documented.

Adverse Reactions

Historical and clinical data report no serious adverse reactions. No serious adverse effects were reported in a Cochrane review of clinical trials of caiapo use in type 2 diabetes.8

Patients with known hypersensitivity reactions to the plant may develop generalized urticaria, hypotension, and edema of the hands and face. Other case reports also document dizziness, loss of consciousness, nausea, vomiting, and a sensation of tickling and tightness in the throat.36

Toxicology

Limited toxicity data are available. Animal studies document temporary neurological effects followed by extensive liver necrosis for 3 sesquiterpenoids in sweet potato, with a median lethal dose ranging from 184 to 266 mg/kg.12 Sweet potato consumption should be avoided in individuals hypersensitive to any of the chemical components of the plant species.36

References

1. Ipomoea batatas. USDA, NRCS. 2017. The PLANTS Database (http://plants.usda.gov, March 2017). National Plant Data Team, Greensboro, NC 27401-4901 USA. Accessed March 2017.
2. Zhao G, Kan J, Li Z, Chen Z. Characterization and immunostimulatory activity of an (1→6)-a-D-glucan from the root of Ipomoea batatas. Int Immunopharmacol. 2005;5(9):1436-1445.15953570
3. Kusano S, Abe H, Tamura H. Isolation of antidiabetic components from white-skinned sweet potato (Ipomoea batatas L.). Biosci Biotechnol Biochem. 2001;65(1):109-114.10227139
4. Yoshimoto M, Okuno S, Yoshinaga M, Yamakawa O, Yamaguchi M, Yamada J. Antimutagenicity of sweetpotato (Ipomoea batatas) roots. Biosci Biotechnol Biochem. 1999;63(3):537-541.13129295
5. Konczak-Islam I, Yoshimoto M, Hou DX, Terahara N, Yamakawa O. Potential chemopreventive properties of anthocyanin-rich aqueous extracts from in vitro produced tissue of sweetpotato (Ipomoea batatas L.). J Agric Food Chem. 2003;51(20):5916-5922.13129295
6. Ludvik B, Waldhäusl W, Prager R, Kautzky-Willer A, Pacini G. Mode of action of Ipomoea batatas (Caiapo) in type 2 diabetic patients. Metabolism. 2003;52(7):875-880.12870164
7. Mohanraj R, Sivasankar S. Sweet potato (Ipomoea batatas [L.] Lam)--a valuable medicinal food: a review. J Med Food. 2014;17(7):733-741.24921903
8. Ooi CP, Loke SC. Sweet potato for type 2 diabetes mellitus. Cochrane Database Syst Rev. 2012;(2):CD009128.22336861
9. Konczak I, Okuno S, Yoshimoto M, Yamakawa O. Caffeoylquinic acids generated in vitro in a high-anthocyanin-accumulating sweet potato cell line. J Biomed Biotechnol. 2004;2004(5):287-292.15577191
10. Goda Y, Shimizu T, Kato Y, et al. Two acylated anthocyanins from purple sweet potato. Phytochemistry. 1997;44(1):183-186.8983218
11. Matsui T, Ebuchi S, Fukui K, Matsugano K, Terahara N, Matsumoto K. Caffeoylsophorose, a new natural alpha-glucosidase inhibitor, from red vinegar by fermented purple-fleshed sweet potato. Biosci Biotechnol Biochem. 2004;68(1):2239-2246.15564660
12. Wilson BJ, Burka LT. Toxicity of novel sesquiterpenoids from the stressed sweet potato (Ipomoea batatas). Food Cosmet Toxicol. 1979;17(4):353-355.520970
13. Ching LS, Mohamed S. Alpha-tocopherol content in 62 edible tropical plants. J Agric Food Chem. 2001;49(6):3101-3105.11410015
14. Maeshima M, Sasaki T, Asahi T. Characterization of major proteins in sweet potato tuberous roots. Phytochemistry. 1985;24:1899-1902.
15. Hayase F, Kato H. Antioxidative components of sweet potatoes. J Nutr Sci Vitaminol (Tokyo). 1984;30(1):37-46.6737096
16. Kano M, Takayanagi T, Harada K, Makino K, Ishikawa F. Antioxidative activity of anthocyanins from purple sweet potato, Ipomoera batatas cultivar Ayamurasaki. Biosci Biotechnol Biochem. 2005;69(5):979-988.15914919
17. Chang WH, Hu SP, Huang YF, Yeh TS, Liu JF. Effect of purple sweet potato leaves consumption on exercise-induced oxidative stress and IL-6 and HSP72 levels. J Appl Physiol (1985). 2010;109(6):1710-1715.20864555
18. Chen CM, Lin YL, Chen CY, Hsu CY, Shieh MJ, Liu JF. Consumption of purple sweet potato leaves decreases lipid peroxidation and DNA damage in humans. Asia Pac J Clin Nutr. 2008;17(3):408-414.18818160
19. Runnie I, Salleh MN, Mohamed S, Head RJ, Abeywardena MY. Vasorelaxation induced by common edible tropical plant extracts in isolated rat aorta and mesenteric vascular bed. J Ethnopharmacol. 2004;92(2-3):311-316.15138017
20. Ren K, Qiu J, Wang X, Niu F, Jiang T. The effect of a sweet potato, footbath, and acupressure intervention in preventing constipation in hospitalized patients with acute coronary syndromes. Gastroenterol Nurs. 2012;35(4):271-277.22847287
21. Matsui T, Ueda T, Oki T, Sugita K, Terahara N, Matsumoto K. Alpha-Glucosidase inhibitory action of natural acylated anthocyanins. 1. Survey of natural pigments with potent inhibitory activity. J Agric Food Chem. 2001;49(4):1948-1951.11308351
22. Kusano S, Abe H. Antidiabetic activity of white skinned sweet potato (Ipomoea batatas L.) in obese Zucker fatty rats. Biol Pharm Bull. 2000;23(1):23-26.10706405
23. Nagamine R, Ueno S, Tsubata M, et al. Dietary sweet potato (Ipomoea batatas L.) leaf extract attenuates hyperglycaemia by enhancing the secretion of glucagon-like peptide-1 (GLP-1). Food Funct. 2014;5(9):2309-2316.25066255
24. Berberich T, Takagi T, Miyazaki A, Otani M, Shimada T, Kusano T. Production of mouse adiponectin, an anti-diabetic protein, in transgenic sweet potato plants. J Plant Physiol. 2005;162(10):1169-1176.16255175
25. Suzuki T, Tada H, Sato E, Sagae Y. Application of sweet potato fiber to skin wound in rat. Biol Pharm Bull. 1996;19(7):977-983.8839973
26. Chen CM, Li SC, Lin YL, Hsu CY, Shieh MJ, Liu JF. Consumption of purple sweet potato leaves modulates human immune response: T-lymphocyte functions, lytic activity of natural killer cell and antibody production. World J Gastroenterol. 2005;11(37):5777-5781.
27. Miyazaki Y, Kusano S, Doi H, Aki O. Effects on immune response of antidiabetic ingredients from white-skinned sweet potato (Ipomoea batatas L.). Nutrition. 2005;21(3):358-362.15797679
28. Suda I, Ishikawa F, Hatakeyama M, et al. Intake of purple sweet potato beverage affects on serum hepatic biomarker levels of healthy adult men with borderline hepatitis. Eur J Clin Nutr. 2008;62(1):60-67.17299464
29. Haskell MJ, Jamil KM, Hassan F, et al. Daily consumption of Indian spinach (Basella alba) or sweet potatoes has a positive effect on total-body vitamin A stores in Bangladeshi men. Am J Clin Nutr. 2004;80(3):705-714.15321812
30. van Jaarsveld PJ, Faber M, Tanumihardjo SA, Nestel P, Lombard CJ, Benadé AJ. Beta-carotene-rich orange-fleshed sweet potato improves the vitamin A status of primary school children assessed with the modified-relative-dose-response test. Am J Clin Nutr. 2005;81(5):1080-1087.
31. Hotz C, Loechl C, Lubowa A, et al. Introduction of β-carotene-rich orange sweet potato in rural Uganda resulted in increased vitamin A intakes among children and women and improved vitamin A status among children. J Nutr. 2012;142(10):1871-1880.22875553
32. Hotz C, Loechl C, de Brauw A, et al. A large-scale intervention to introduce orange sweet potato in rural Mozambique increases vitamin A intakes among children and women. Br J Nutr. 2012;108(1):163-176.22018075
33. Jamil KM, Brown KH, Jamil M, et al. Daily consumption of orange-fleshed sweet potato for 60 days increased plasma β-carotene concentration but did not increase total body vitamin A pool size in Bangladeshi women. J Nutr. 2012;142(10):1896-1902.22933750
34. Turner T, Burri BJ, Jamil KM, Jamil M. The effects of daily consumption of β-cryptoxanthin-rich tangerines and β-carotene-rich sweet potatoes on vitamin A and carotenoid concentrations in plasma and breast milk of Bangladeshi women with low vitamin A status in a randomized controlled trial. Am J Clin Nutr. 2013;98(5):1200-1208.24004891
35. Ludvik BH, Mahdjoobian K, Waldhaeusl W, et al. The effect of Ipomoea batatas (Caiapo) on glucose metabolism and serum cholesterol in patients with type 2 diabetes: a randomized study. Diabetes Care. 2002;25(1):239-240.11772921
36. Velloso A, Baeza M, Tornero P, et al. Anaphylaxis caused by Ipomoea batatas. J Allergy Clin Immunol. 2004;113:S242.

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