Food as Medicine: Kiwifruit (Actinidia deliciosa, Actinidiaceae)

Kiwifruit (Actinidia deliciosa, Actinidiaceae), also known by the less common name “Chinese gooseberry,” is one of 50 known species within the genus Actinidia.1 These species are climbing, woody vines with large, heart-shaped leaves and cream-colored flowers that bloom in the spring. The flowers are dioecious, with male and female blossoms found in separate individuals. The kiwifruit matures in early winter and typically has brown fuzzy skin. Depending on the species, the flesh is either green or yellow, but all species are filled with small black, edible seeds.1 While A. deliciosa accounts for about 90% of kiwifruit in international trade, two other species are cultivated and sold commercially: A. Chinensis and A. arguta.2 Actinidia deliciosa is the common green kiwifruit.3 The most common cultivar of A. chinensis is “Hort16A,” known by the brand name ZESPRI, or “gold kiwifruit.”4Actinidia arguta is referred to as “baby kiwi” or “grape kiwi” due to the small size of its fruits.2Actinidia species are native to southwestern China, but they are now cultivated in New Zealand, the United States, Italy, France, Chile, and Japan.5

Phytochemicals and Constituents

Kiwifruit provides fiber, potassium, folate, phosphorus, copper, and vitamins A, C, E, and K.3,6 In fact, one kiwifruit provides more than the Recommended Dietary Allowance (RDA) of vitamin C for adults and almost 35% of the RDA of vitamin K. Vitamin C has numerous health benefits, including anticarcinogenic and immune-regulating properties.3,7 In addition, it plays a role in the formation of collagen, a major component of connective tissue, skin, and bones. Vitamin C intake also has been shown to help mitigate a number of conditions, including cardiovascular disease and inflammation.8 Vitamin E is an antioxidant that stops the oxidation of low-density lipoprotein (LDL) cholesterol and protects cell membranes against damage caused by reactive oxygen species.9 Vitamin E also helps maintain the structure and function of skeletal, cardiac, and smooth muscles. Vitamin K regulates blood clotting, aids in the transfer of calcium through the body, and supports bone health, reducing the risk of osteoporosis and bone fractures due to age.10

Kiwifruit is also a good source of fiber, which contributes to its laxative effect. Additionally, the lignins in cellulose (a form of dietary fiber) are believed to have antimutagenic properties due to their ability to increase the adsorption of aromatic amines in the gut, thus preventing them from entering the bloodstream. Aromatic amines can act as carcinogens after they have been metabolized by the liver.3

One of the interesting compounds present in kiwifruit is actinidin, an enzyme that helps to hydrolyze proteins. Due to the actinidin content of kiwifruit, other fruits and dairy products will soften or curdle upon prolonged contact with the chopped fruit, so kiwifruit should be added at the last minute to fruit salads and other mixed preparations. Actinidin has been shown to improve digestion by assisting with protein digestion and digestive motility.11 Kiwifruit contains numerous other bioactive compounds, including organic acids, plant pigments, and polyphenols. The primary organic acid in kiwi is citric acid, but it also contains malic, quinic, gallic, and oxalic acids. Organic acids provide the fruits with significant antioxidant properties.

Some of the plant pigments present in kiwifruit include carotenoids and chlorophyll, and some cultivars also contain anthocyanins.11 The carotenoids include beta-carotene, lutein, violaxanthin, and 9’-cis-neoxanthin.3 When compared with other commonly consumed fruits, kiwifruit is the richest source of lutein, which is a carotenoid that is highly concentrated in the macula of the eye and is associated with lowering risk of cataracts. All Actinidia species contain chlorophylls a and b, but levels are much lower in the gold kiwi variety. Some kiwifruits also contain anthocyanins, but they are not a significant component of the antioxidant capacity of the fruit. Glutathione is another important antioxidant present in kiwifruit, and it not only prevents oxidative damage of cells but also helps to keep vitamins C and E in their active form, regenerating their antioxidant capacities.11

Historical and Commercial Uses

Kiwifruit is featured in Chinese literature dating back to the 15th century.12 The kiwifruit was originally called mi hou tao, or “monkey peach,” because monkeys would eat the fruit in the wild.4 Traditionally, both the root and the fruit of A. chinensis were used in traditional Chinese medicine and are known as xiao yang tao. The root of A. Chinensis contains antiangiogenic phytochemicals including triterpenes, polyphenols, and anthraquinones, and it has been noted in the Chinese pharmacopeia as being useful for treating many diseases, such as stomach, rectal, and breast cancers, as well as hepatitis viral infections.12-14 The fruit of A. Chinensis was used as a juice to quench thirst, aid digestion, clear heat, and reduce irritability, inflammation, and vomiting.3,14

Other Actinidia species were used for their therapeutic effects as well. Historically, A. macrosperma was used to stimulate the immune system and A. polygama was used as an anti-inflammatory agent and to counteract allergies due to its anti-asthmatic effect.3,15

Modern Research

Clinical trials for kiwifruit primarily have focused on its effects on the digestive, immune, and cardiovascular systems. Preliminary research has also investigated the antioxidant properties of kiwifruit and its possible inhibitory effect on cancerous cell growth.

Gastrointestinal System

Clinically, kiwifruit has been shown to have a laxative effect. Daily consumption of the fruit improved the frequency and ease of bowel movements and improved stool bulk and softness in healthy older adults.3 In another study, researchers found that daily kiwifruit intake relieved symptoms in subjects suffering from chronic constipation, with no reports of adverse effects like diarrhea.3 Additionally, a trial in healthy subjects who were not experiencing constipation found no adverse gastrointestinal effects from daily consumption of kiwifruit.16

These gastrointestinal benefits are attributed to the lubricating effects of kiwifruit’s pectin and the enzyme actinidin, which combine with the enzymes in the stomach and the small intestine to improve digestion.4The pectin and fiber present in kiwifruits also function as prebiotics. Prebiotics help to modify the composition of the bacterial flora in the gut so that healthy bacteria are stimulated and harmful bacteria are suppressed. An in vitro study looked at the prebiotic effect of the pectin present in kiwifruit compared to other prebiotics like inulin, guar gum, and citrus pectin. The pectin in kiwifruit was more effective than these prebiotics in reducing the intestinal adhesion of harmful bacteria and increasing the adhesion of beneficial bacteria.17 In a mouse study on irritable bowel disease (IBD), extracts of both green and golden kiwifruit were administered, resulting in a potent anti-inflammatory effect. These results indicate that further research should be done exploring the medicinal properties of kiwifruits in the treatment of IBD.18

Antibacterial and Immunological Activity

In an in vitro study, essential oil from A. macrosperma produced inhibitory effects against a number of common bacteria, including Escherichia coli and Staphylococcus aureus, as well as three common fungal species.3 In a mouse study, kiwifruit extract was shown to alter innate and acquired immunity when the mice were injected with cholera and diphtheria/tetanus vaccines.15 This could have implications for improving immunity in vaccinated individuals, particularly children and other high-risk populations.

Other animal studies have shown that extracts of A. arguta may have anti-allergenic effects, implying a potential for the use of kiwi extracts as therapies for allergy conditions like bronchial asthma or eczema.3 A human trial observed the effects of daily intake of golden kiwifruit on both older adults (older than 65 years) and young children (ages 2-5) in relation to cold and flu-like illnesses. For the adults, those who ate four kiwifruits daily had symptoms for fewer days over the course of a cold than the adults who ate two bananas (Musa acuminata, Musaceae) daily. In the preschool children, the odds of getting a cold or the flu decreased by almost half in the children who ate two kiwifruits daily instead of one banana.4

Cardiovascular System

There is some evidence that kiwifruit may have the ability to affect risk factors for cardiovascular disease, like blood pressure, plasma triglycerides, and platelet aggregation. A human study showed that eating two to three kiwifruits per day reduced triglyceride levels by 15% and reduced platelet aggregation response by18% compared to control.19Multiple studies have shown that daily kiwi consumption improves not only triglyceride levels but also the ratio of total cholesterol to high-density lipoprotein (HDL) cholesterol. One clinical trial studied male smokers who ate three kiwis per day for eight weeks. The patients had significantly reduced blood pressure and angiotensin-converting enzyme (ACE) activity (a component of the blood pressure-regulation process), especially those with hypertension. A number of in vitro studies support the claim that kiwifruit reduces platelet aggregation, but clinical trials are conflicting and more human studies are needed to confirm this effect.4

Antioxidant and Cytotoxic Properties

The vitamin and phytochemical composition of kiwifruit give it powerful antioxidant properties. An in vivo study showed that kiwifruit juice ingestion increased plasma antioxidant capacity within 30 minutes and that these levels were sustained for up to 90 minutes. Though this was not a long-term study, this may have implications for kiwifruit’s ability to fight oxidative stress.3 Similar findings were established through two human studies in the United Kingdom, which showed that kiwifruit consumption improved antioxidant status of both the plasma and lymphocytes of participants. One of these studies also showed that kiwifruit seemed to stimulate DNA repair. A pilot study was performed to extrapolate on this possibility and the results showed that kiwi aided DNA repair for an average of 13 hours after ingestion.7

Though vitamin C is known for its antioxidant power, it also has a synergistic effect on iron absorption. In a study of young women with mild anemia (iron deficiency), participants who consumed two golden kiwifruits with an iron-fortified cereal daily had significantly improved iron levels compared to participants who ate the cereal with a banana. The vitamin C content, along with the carotenoids lutein and zeaxanthin present in kiwifruits, are likely responsible for this outcome.4

There is a great deal of investigation into the role of antioxidants and other phytochemicals in the prevention of cancerous cell growth, but despite kiwifruit’s history of use in traditional Chinese medicine, there are few clinical trials establishing the connection of the fruit and its constituents with cancer prevention or treatment. In vitro studies have shown that extracts of Actinidia species may be toxic to cancer cells. Additionally, mice studies have shown that kiwifruit juice inhibits the growth of sarcoma cells.12 Another mouse study showed that catechin in the stems of A. arguta and the juice of A. deliciosa increased bone marrow proliferation, which may have implications for reducing the adverse effects of chemotherapy treatments. There has also been evidence suggesting that the prebiotic effect of fiber found in foods may change the bacteria in the colon, providing protection against colon cancer.3

Consumer Considerations

Though it is poorly understood, there is an allergy risk associated with the fruits of Actinidia species. Allergic reactions can range from mild itching of the throat, mouth, and lips, and swelling to anaphylaxis, though it is more common for reactions to be mild. The more severe reactions typically occur in children.4The prevalence of allergies to Actinidia fruits may vary geographically; in France, Finland, and Sweden, kiwifruit is one of the top ten most common allergens.16 Allergies to kiwifruit are often cross-reactive with other common allergens such as pollens, rye (Secale cereale, Poaceae), hazelnut (Corylus avellana, Betulaceae), chestnut (Castanea spp., Fagaceae), banana, and avocado (Persea Americana, Lauraceae). Heat treatment and industrial homogenization have been shown to greatly reduce the allergic reactivity of green kiwi. These treatments are often performed on processed products like beverages and jams.20

Kiwifruit contains oxalate, which is from the salt of oxalic acid. Oxalates can cause oral irritation in some individuals, and they can be risky for individuals with a history of calcium oxalate-containing kidney stones. Oxalate in high concentrations can also reduce the bioavailability of calcium, magnesium, and iron in the body.3 Though kiwifruit contains more than 10 mg of oxalate per serving (enough to be considered high levels), it would require daily consumption of large quantities of kiwifruit for the levels of oxalates in the body to become dangerous. Additionally, oxalate content decreases during storage.16

Nutrient Profile21

Macronutrient Profile: (Per one fruit [approx. 69 grams])

42 calories
0.8 g protein
10.1 g carbohydrate
0.4 g fat

Secondary Metabolites: (Per one fruit [approx. 69 grams])

Excellent source of:

Vitamin C: 64 mg (106.7% DV)
Vitamin K: 27.8 mcg (34.8% DV)

Good source of:

Dietary Fiber: 2.1 g (8.4% DV)
Potassium: 215 mg (6.1% DV)
Vitamin E: 1 mg (5% DV)

Also, provides:

Folate: 17 mcg (4.3% DV)
Manganese: 0.07 mg (3.5% DV)
Magnesium: 12 mg (3% DV)
Calcium: 23 mg (2.3% DV)
Phosphorus: 23 mg (2.3% DV)
Vitamin B6: 0.04 mg (2% DV)
Thiamin: 0.02 mg (1.3% DV)
Niacin: 0.24 mg (1.2% DV)
Riboflavin: 0.02 mg (1.2% DV)
Vitamin A: 60 IU (1.2% DV)
Iron: 0.2 mg (1.1% DV)

DV = Daily Value as established by the US Food and Drug Administration, based on a 2,000-calorie diet.

Recipe: Kiwi, Lemon, and Rosemary Shrub

Courtesy of Jerry James Stone22

Ingredients:

  • 1 1/2 pounds kiwifruit
  • 2 slices of lemon
  • 1 sprig of rosemary
  • 1 cup sugar
  • 1 cup champagne vinegar

Directions:

  1. Peel and thinly slice the kiwifruit. Arrange a layer of kiwifruit in a quart-sized jar and sprinkle with sugar. Repeat the layering until all the sugar and fruit is in the jar. Seal and let stand for five hours.

  2. Add the lemon, rosemary, and vinegar to the jar. Seal and shake to combine and dissolve the sugar, then let stand for 24 hours.

  3. Strain the mixture through a sieve into a clean quart-sized jar. Seal and refrigerate. To serve, mix two tablespoons of the shrub with sparkling water in an ice-filled glass.

References

  1. The National Geographic Society. Edible: An Illustrated Guide to the World’s Food Plants. Washington, DC: The National Geographic Society; 2008.
  2. Wojdyło A, Nowicka P, Oszmiański J, Golis T. Phytochemical compounds and biological effects of Actinidia fruits. J Funct Foods. 2017;30:194-202. doi:10.1016/j.jff.2017.01.018.
  3. Hunter DC, Skinner MA, Ferguson AR, Stevenson LM. Kiwifruit and health. In: Bioactive Foods in Promoting Health: Fruits and Vegetables. Auckland, New Zealand; 2010:565-580. doi:10.1016/B978-0-12-374628-3.00037-2.
  4. Stonehouse W, Gammon CS, Beck KL, Conlon C, von Hurst PR, Kruger R. Kiwifruit: our daily prescription for health. Can J Physiol Pharmacol. 2013;91(6):442-447. doi:10.1139/cjpp-2012-0303.
  5. van Wyk B-E. Food Plants of the World: An Illustrated Guide. Portland, OR: Timber Press; 2005.
  6. Murray M, Pizzorno J, Pizzorno L. The Encyclopedia of Healing Foods. New York, NY: Atria Books; 2005.
  7. Rush E, Ferguson LR, Cumin M, Thakur V, Karunasinghe N, Plank L. Kiwifruit consumption reduces DNA fragility: a randomized controlled pilot study in volunteers. Nutr Res. 2006;26(5):197-201. doi:10.1016/j.nutres.2006.05.002.
  8. Carr AC, Pullar JM, Moran S, Vissers MCM. Bioavailability of vitamin C from kiwifruit in non-smoking males: determination of “healthy” and “optimal” intakes. J Nutr Sci. 2012;1:e14. doi:10.1017/jns.2012.15.
  9. Weil A, Becker B. Facts about vitamin E. Weil website. August 2016. Available at: www.drweil.com/vitamins-supplements-herbs/vitamins/facts-about-vitamin-e/. Accessed June 21, 2017.
  10. Ehrlich SD. Vitamin K. University of Maryland Medical Center website. July 16, 2013. Available at: www.umm.edu/health/medical/altmed/supplement/vitamin-k. Accessed June 22, 2017.
  11. Drummond L. Chapter three — The composition and nutritional value of kiwifruit. Adv Food Nutr Res. 2013;68:33-57. doi:http://dx.doi.org/10.1016/B978-0-12-394294-4.00003-1.
  12. Motohashi N, Shirataki Y, Kawase M, et al. Cancer prevention and therapy with kiwifruit in Chinese folklore medicine: A study of kiwifruit extracts. J Ethnopharmacol. 2002;81(3):357-364. doi:10.1016/S0378-8741(02)00125-3.
  13. Zhu WJ, Yu DH, Zhao M, et al. Antiangiogenic triterpenes isolated from Chinese herbal medicine Actinidia chinensis Planch. Anti-Cancer Agents Med Hist. 2013;13(2):195-198. doi:10.2174/187152013804711146.
  14. Hsu HY. Oriental Materia Medica: A Concise Guide. Long Beach, CA: Oriental Healing Arts Institute; 1986.
  15. Shu Q, Mendis De Silva U, Chen S, et al. Kiwifruit extract enhances markers of innate and acquired immunity in a murine model. Food Agric Immunol. 2008;19(2):149-161. doi:10.1080/09540100802117198.
  16. Singletary K. Kiwifruit. Nutr Today. 2012;47(3):133-147. doi:10.1097/NT.0b013e31825744bc.
  17. Parkar SG, Redgate EL, Wibisono R, Luo X, Koh ETH, Schröder R. Gut health benefits of kiwifruit pectins: Comparison with commercial functional polysaccharides. J Funct Foods. 2010;2(3):210-218. doi:10.1016/j.jff.2010.04.009.
  18. Edmunds SJ, Roy NC, Love DR, Laing WA. Kiwifruit extracts inhibit cytokine production by lipopolysaccharide-activated macrophages, and intestinal epithelial cells isolated from IL10 gene deficient mice. Cell Immunol. 2011;270(1):70-79. doi:10.1016/j.cellimm.2011.04.004.
  19. Park YS, Leontowicz H, Leontowicz M, et al. Comparison of the contents of bioactive compounds and the level of antioxidant activity in different kiwifruit cultivars. J Food Compos Anal. 2011;24(7):963-970. doi:10.1016/j.jfca.2010.08.010.
  20. Nishiyama I. Fruits of the Actinidia genus. Adv Food Nutr Res. 2007;52(6):293-324. doi:10.1016/S1043-4526(06)52006-6.
  21. Basic Report: 09148, Kiwifruit, green, raw. United States Department of Agriculture Agricultural Research Service website. May 2016. Available at: https://ndb.nal.usda.gov/ndb/foods/show/2253. Accessed June 22, 2017.
  22. Stone JJ. Kiwi, lemon & rosemary shrub (drinking vinegar). Jerry James Stone website. December 4, 2013. Available at: jerryjamesstone.com/recipe/kiwi-lemon-rosemary-shrub-drinking-vinegar/. Accessed June 22, 2017. [Editor’s note: The linked webpage contains profanity.]
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