January 2020 Issue
Pomegranates — Crimson-Colored Fruit Packing a Wallop of Antioxidants That May Help Prevent Chronic Disease
By KC Wright, MS, RDN, LD
Today’s Dietitian
Vol. 22, No. 1, P. 32
In ancient times, pomegranates were revered as symbols of prosperity and fertility; in the modern era, the fruit has gained considerable recognition as a functional food due to its high antioxidant content.
The pomegranate is native to the region of Iran to northern India and has been cultivated throughout the Mediterranean, Africa, and Europe. Spanish settlers brought pomegranates to California, currently the largest grower of the fruit in the United States.1 These bright crimson orbs with crownlike stems are grown on a large shrub or small tree, about 20 to 30 feet high. From a distance, the pomegranate shrub can be mistaken for an apple tree. In fact, “pomegranate” comes from the French word for apple, pomme, and the Latin word granatum, meaning “seeded.”
In addition to being rich in antioxidant polyphenols, a pomegranate comprises approximately 80% water and 16% sugar and is a good source of potassium and vitamin C.2 Due to pomegranate’s high polyphenol content, it’s been touted as one of the distinguished edibles that’s classified as a “superfood”—a popular buzzword in the language of food and health.
Culinary and Medicinal Uses
Pomegranate seeds are covered with a fleshy outgrowth, known as an aril, that resembles a ruby red jewel. Hundreds of arils compose the heart of the fruit. They have a juicy and refreshing taste with hints of sweetness and citrus. Arils can be eaten raw out of hand; added to cereals, oatmeal, smoothies, salads, beverages, desserts, and other dishes; or pressed for juice.
Pomegranate juice generally is available commercially bottled, as a juice concentrate, or as an extract (typically in pill form.) One 8-oz cup of juice can range in polyphenol content from 480 to 2,400 mg, whereas supplements of extract offer 250 to 1,000 mg. Commercial pomegranate juice made from the fruit’s arils and rind has greater antioxidant activity than juice made from the arils alone. The health benefits of pomegranate juice, particularly its anti-inflammatory properties, have been especially extolled.3
The pomegranate fruit, leaves, flowers, and seeds all have been used for teas in traditional herbal medicine, as the fruit goes back as far as the history of agriculture itself.1,4 In the ancient Ayurveda system of medicine, the pomegranate was used extensively as a source of traditional remedies for thousands of years.5 Pomegranate juice was used in preparations for dyspepsia and leprosy, while extracts of pomegranate tree bark, leaves, fruit rind, and immature fruit were offered as remedies for bleeding, diarrhea, dysentery, and intestinal parasites. Dried pomegranate flowers have been used for bronchitis and a decoction of the flowers to relieve swelling in the mouth and throat.2
Research Findings
The bioactive properties of pomegranate polyphenols, along with the advancement in analytical technologies, have spurred vast interest in researching the fruit especially within the last decade. As of 2017, more than 1,500 articles were published about pomegranates, with most of them published between 2006 and 2016.6 Much of the research has linked pomegranate polyphenols, particularly anthocyanins and tannins, to health promotion. Anthocyanins are colorful, water-soluble polyphenol pigments found in many plant foods, including pomegranates and berries. They’ve been linked to human disease prevention and treatment due to their anti-inflammatory and cardioprotective properties.7
Various phytochemicals are present in different pomegranate tissues. Specifically, a group of health-promoting phenolic metabolites called urolithins, transformed from ellagic acid (a hydrolysis product of pomegranate ellagitannins by the human gut microbiota) have been investigated.
Despite the abundance of research on the purported effects of pomegranate fruit and extract on chronic inflammatory diseases and other inflammation-related diseases, a definitive relationship between the consumption of pomegranate products and their beneficial properties hasn’t yet been established.8 The most promising properties of pomegranates thus far are related to their effect on diabetes, metabolic syndrome, and CVDs.
Pomegranate juice has shown therapeutic potential for many illnesses, but most of the scientific research has been done in animal or cell culture models. Thus, there’s limited scientific evidence that evaluates the influence of pomegranate on reducing disease implications in humans. Furthermore, clinical trials have yet to establish the dose or form of pomegranate juice that’s effective in the treatment or prevention of any disease. According to ConsumerLab.com (a leading provider of independent test results and information to help both consumers and health care professionals identify the best-quality health and nutrition products), one of the challenges with research on pomegranates may stem from the fact there’s a vast difference in the levels of polyphenols among commercial products.2 For example, researchers at UCLA tested commercial pomegranate extract supplements for levels of polyphenols and found enormous variation among products¬—some of which contained significant amounts, while others contained trace amounts and still others had no detectable amounts. It’s unknown whether polyphenols are converted to other compounds during processing, or whether the products were altered or “spiked” with antioxidants to meet label claims on the products.4
Urolithins have been studied in enzyme assays to assess a potential role in breast cancer, where they exhibit antiaromatase properties, reducing the conversion of androgens to estrogens. Urolithins also have been shown to reduce the proliferation of endometrial cancer cells, though the mechanism of action has yet to be determined. Several studies suggest that urolithins may be chemopreventive agents against prostate cancers, through different mechanisms in androgen-sensitive, -responsive, and -independent cells.6
In vitro studies with neutrophils, monocytes, and nitric oxide suggest potential anti-inflammatory and cardiovascular-protective functions of urolithins. Urinary excretion of urolithins by healthy volunteers after ingesting ellagitannin-rich food or fruit extracts demonstrated an interlinked relationship between microbial imbalance and ellagitannin metabolism, suggesting that ellagitannins may influence gut-producing bacteria that in turn may reduce the effects associated with obesity.6
One small study of 16 healthy volunteers compared the acute effect of pomegranate juice with that of a polyphenol-rich extract on a bread-derived postprandial blood glucose concentration in two randomized, crossover, controlled studies (double-blinded for the supplements).9 Outcome data showed that pomegranate polyphenols in a beverage, but not in a supplement, can help reduce the postprandial glycemic response of bread.
Results from a double-blinded, randomized, placebo-controlled clinical trial published this year suggest that dietary supplementation of urolithin A (UA), a pomegranate metabolite, could offer an antiaging benefit due to its impact on mitochondrial and cellular health.10 Healthy, sedentary, elderly subjects were given doses of UA over a four-week period. The UA was found to be bioavailable in plasma with observed effects on mitochondrial biomarkers, suggesting that UA induces improved mitochondrial and cellular health—a natural process that typically declines in function with advanced age. It’s important to recognize that this research was sponsored by the life science company Amazentis, whose lead product is UA. Amazentis proclaims this research as the “First human clinical trial results on an antiaging compound … a breakthrough for translational science of dietary supplementation with urolithin A.” Amazentis, a Swiss company, has partnered with Nestlé to use the patented product in foods and beverages. This study demonstrates the need for RDs to discern objectivity or bias in nutrition research.
Well-designed human studies are needed to substantiate preliminary research findings on the effects of pomegranate on health and disease. The National Institutes of Health is funding several ongoing studies to evaluate the effects of pomegranate on health and various diseases.11-14
Practice Points for RDs
Due to its reported health benefits, the regal pomegranate attracts many consumers. Whole pomegranate fruit, bottled juice, and harvested, prepackaged arils are available in the produce department of most markets from October through January. Pomegranate also is sold in functional food ingredients, dietary supplements, teas, jams, jellies, wine, and spices prepared from dried seeds.
Pomegranate arils comprise about one-half of the weight of the whole fruit. Recommend clients choose fruits that feel heavy for their size. The skin should appear taut, thin, and smooth. Pomegranates should be stored in a dark cool place; whole fruits remain intact for as long as two months in the refrigerator.
The sweet edible arils are high in vitamin B6, vitamin C, and potassium.2 Pomegranate juice is processed as 100% pomegranate, which may be rather tart, or combined with other fruits for a juice blend that may be more palatable and less expensive. As commercial pomegranate products vary in the amounts of polyphenols per serving, read the labels for any information on the type or amount of polyphenols contained. Pomegranate juice doesn’t appear to interfere with the absorption or metabolism of any medications.15
Consumers with weight management and blood glucose concerns need to be aware that an 8-oz serving of pomegranate juice from concentrate contains 150 kcal, 32 g sugar, and no fiber. These individuals would be better served by consuming 1/4 cup of whole pomegranate arils, which contains 36 kcal, 6 g sugar, and almost 2 g fiber.
— KC Wright, MS, RDN, LD, is a research dietitian at Dartmouth-Hitchcock Medical Center and maintains a nutrition communications practice. She advocates for good food and sustainable food systems at www.wildberrycommunications.com.
[Sidebar]
EXTRACTING ARILS FROM POMEGRANATE FLESH
To the novice, extracting the arils from inside a pomegranate can seem a bit daunting, but there are several methods that simply take some practice. Seeking advice from how-to videos on YouTube can be especially helpful. Always wash the outside of the pomegranate well before cutting.
Method 1
One of the easiest and fastest methods is to run a small sharp knife around the fruit, slicing about 1/2 inch deep. Hold both halves while twisting them apart. Hold one half of the pomegranate with the cut side open over a large bowl. Use a large wooden spoon to yield hefty taps on the fruit, hard enough so the arils fall out into the bowl. Then repeat with the other half. Finally, pick out any bits of white tissue that also may have fallen into the bowl. The main drawback to this method is that the arils may break apart, making a bit of a mess and causing a loss of some of the juice.
Method 2
Run a small sharp knife around the fruit, about 1/2 inch deep. Hold both halves while twisting them apart. Immerse the two halves in a large bowl full of cold water and gently remove the arils from the inside tissue. The arils will sink while the white bits will float so they’re easy to remove.
Method 3
Carefully cut an opening at either the top or bottom of the pomegranate to remove the cap. Then run the knife through the peel to make wedges, trying to avoid cutting any arils. Open the pomegranate carefully and separate into the wedges. Drop the seeds in the bowl with your fingers. This may be the slowest method, but the arils won’t be wet and likely will sustain less damage.
— KW
References
1. Pomegranates. Agricultural Marketing Resource Center website. https://www.agmrc.org/commodities-products/fruits/pomegranates. Updated February 2019. Accessed September 15, 2019.
2. Pomegranate juice and supplements review article. ConsumerLab.com website. https://www.consumerlab.com/reviews/Pomegranate_Juice_and_Supplements/pomegranate/. Updated December 19, 2007. Accessed September 16, 2019.
3. Taufer J. Pomegranate health benefits. University of Florida/Institute of Food and Agricultural Sciences Citrus Extension website. https://crec.ifas.ufl.edu/extension/pomegranates/health.shtml. Updated June 19, 2018.
4. Kader AA. Postharvest biology and technology of pomegranates. In: Seeram NP, Schulman RN, Heber D, eds. Pomegranates: Ancient Roots to Modern Medicine. Boca Raton, FL: CRC Press; 2006:211-222.
5. Bhowmik D, Gopinath H, Kumar BP, Duraivel S, Aravind G, Kumar KPS. Medicinal uses of Punica granatum and its health benefits. J Pharmacogn Phytochem. 2013;1(5):28-35.
6. Wu S, Tian L. Diverse phytochemicals and bioactivities in the ancient fruit and modern functional food pomegranate (Punica granatum). Molecules. 2017;22(10):E1606.
7. Zarfeshany A, Asgary S, Javanmard SH. Potent health effects of pomegranate. Adv Biomed Res. 2014;3:100.
8. Danesi F, Ferguson LR. Could pomegranate juice help in the control of inflammatory diseases? Nutrients. 2017;9(9):E958.
9. Kerimi A, Nyambe-Silavwe H, Gauer JS, Tomás-Barberán FA, Williamson G. Pomegranate juice, but not an extract, confers a lower glycemic response on a high-glycemic index food: randomized, crossover, controlled trials in healthy subjects. Am J Clin Nutr. 2017;106(6):1384-1393.
10. Andreux PA, Blanco-Bose W, Ryu D, et al. The mitophagy activator urolithin A is safe and induces a molecular signature of improved mitochondrial and cellular health in humans. Nat Metab. 2019;1:595-603.
11. Effect of inorganic nitrate supplement on blood pressure. ClinicalTrials.gov website. https://clinicaltrials.gov/ct2/show/NCT03909789?term=pomegranate&draw=23&rank=79. Updated April 12, 2019.
12. Pomegranate juice in treating patients with recurrent prostate cancer. ClinicalTrials.gov website. https://clinicaltrials.gov/ct2/show/NCT00060086?term=pomegranate&draw=3&rank=30. Updated May 7, 2019.
13. Dietary intervention in follicular lymphoma (KLYMF). ClinicalTrials.gov website. https://clinicaltrials.gov/ct2/show/NCT00455416?term=pomegranate&draw=11&rank=95. Updated May 21, 2008.
14. Anti-oxidative influence from pomegranate tablets on male sperm quality in couples undergo infertility treatments due to male infertility (pomegranate). ClinicalTrials.gov website. https://clinicaltrials.gov/ct2/show/NCT01918163?term=pomegranate&rank=1. Updated August 7, 2013.
15. Ask Tufts experts. Tufts University Health & Nutrition Letter website. https://www.nutritionletter.tufts.edu/issues/6_1/ask-experts/ask-tufts-experts_1104-1.html. Published January 2010.