HerbalEGram: Volume 15, Issue 12, December 2018

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. We would like to acknowledge ABC Chief Science Officer Stefan Gafner, PhD, for his contributions to this project.

By Jenny Perez^a and Hannah Bauman^b

^a ABC Education Coordinator

^b HerbalGram Associate Editor

Overview

The genus Pyrus consists of 30 deciduous species and is closely related to the genus Malus, which includes apples (Malus spp.). Both genera are part of the economically important Rosaceae family.^1,2 Similar to apples, Pyrus fruits are classified as pomes, where the seeds are contained in a central, compartmentalized core.³ The Pyrus genus is native to Europe, Asia, the Middle East, and North Africa.¹ Capable of living more than 250 years, the pear tree is one of the longest-living fruit trees.¹ Cultivated pears are derived from one or two wild pear species widely distributed in Europe and western Asia.² Of the 5,000 varieties cultivated worldwide, the two species grown commercially are the European pear (P. communis) with its juicy, aromatic, bell-shaped fruit, and the Asian pear (P. pyrifolia) with its crisp and crunchy, apple-like shape and texture.^1,2,

The European pear is a medium-sized tree that grows to 30-50 feet with a narrow canopy and alternate, glossy green leaves that are oval or lanceolate in shape.^1,2 The Asian pear grows to 30 feet and has green, oblong, alternately attached leaves that appear orange and bronze in autumn. Both species have small, white, five-petaled flowers with numerous stamens that emerge just prior to the leaves in spring.^1,2 

Historical and Commercial Uses

Both the Asian pear and the European pear were domesticated in their respective countries of origin approximately 3,000 years ago. Asian pears were originally grown in China, Japan, and Korea, while the European pear was domesticated in France, Germany, and Belgium.³ In 1620, the first pear tree in America was planted by colonists.⁴ In addition to its edible fruit, the pear tree is valued for its ornamental beauty as well as its wood, which is used to manufacture furniture and woodwind instruments.²

For thousands of years, pear fruits have been used as medicine in both traditional Chinese medicine (TCM) and Ayurvedic practices. In both Ayurveda and TCM, Asian pears are considered sweet and cooling and are used to manage respiratory diseases such as asthma, rhinitis, and bronchitis.^3,5 Pears also are considered antitussive and are used to soothe coughs, clear phlegm, and relieve inflammation.³ In general, pears are used for their anti-hyperglycemic and diuretic properties, while pear juice (Asian pears specifically) is used to treat shortness of breath during hot days and as a prophylactic to prevent hangovers from alcohol consumption.^3,5 Pear peel is utilized in cosmetics for the skin-whitening properties attributed to its arbutin content. In Ayurveda, pears are used as a natural face and body scrub to reduce dryness, tone the skin, and treat acne.⁵

Pears are commercially produced in at least 81 countries with a global annual yield of approximately 40 billion pounds of fruit.² China leads the world with more than 50% of pear production, followed by Italy and the United States.^2,4 Within the United States, Washington, Oregon, and California are the leading pear producers.² Like other fruit trees in the rose family, many European pear trees require 900-1,000 chill hours (i.e., hours of exposure to temperatures between 32°F and 45°F) in order to break dormancy, bloom, and set fruit.² The most popular varieties of European pear include Bartlett, d’Anjou, Bosc, Comice, Seckel, and Winter Nelis. The Bartlett pear accounts for 75% of US pear production and is the most common pear cultivar in the world.² Asian pear cultivars have lower chill requirements and can therefore be cultivated in warmer climates.² Unlike European pears, Asian pears are allowed to fully ripen on the tree before harvest.²

While commonly considered a dessert fruit, pears were once widely used to make hard pear cider known as “perry.”¹ While perry consumption has seen a decline since the 1970s, there has been a renewed consumer interest in many countries in recent years. In European countries like Austria, Germany, and Switzerland, hard cider made from mixtures of apple and pear juices is still popular. Pear pomace (the remaining skin, seeds, and core post-processing) has been studied for its potential as a fiber supplement to fortify low-fiber food products, such as baked goods.³

Phytochemicals and Constituents

According to the 2001-2010 National Health and Nutrition Examination Survey (NHANES) study, pears are the 11th most commonly consumed fruit in the United States.⁶ Pears contain a high amount of digestion-regulating carbohydrates, specifically fructose, sorbitol, and both soluble and insoluble fiber.^3,4 In fact, pears have a higher pectin content than apples.⁴ Pectin acts like a sponge throughout the digestive system, absorbing water, removing waste and toxins, and lowering cholesterol.^4,7 The consumption of one medium-sized pear daily could enhance bowel transit time and meet nearly 25% of the adult daily dietary fiber requirement.³

Pear is also a good source of potassium and vitamin C.⁹ Potassium is essential for healthy muscles, nervous system function, and blood pressure levels. Vitamin C helps regulate metabolism and enhances wound healing, tissue repair, and immune function.⁹ According to the healthy eating index (HEI), individuals who consume pears were more likely to have higher-quality diets and consume higher amounts of vitamin C, magnesium, copper, dietary fiber, and potassium than those who do not consume pears.⁶

Pears have a unique sugar profile due to their higher content of fructose compared to sucrose and glucose. Fructose gives pears their characteristic sweet taste and is a rich source of sorbitol, a natural fruit sugar alcohol that is poorly absorbed and associated with a laxative effect when consumed in excess.³ Despite their sweet taste, pears have, on average, a glycemic index (GI) value of 38, which is comparable to apples and, as it is a GI score under 55, considered low. Eating foods with a low GI value is important for both weight and blood sugar management as these foods are digested and absorbed more slowly and have a minimal impact on blood glucose levels.³

The phenols abundant in pear fruit and peel include arbutin, flavonoids, and phenolic acids. The most abundant flavonoids in pears are catechins (flavan-3-ol monomers and polymers) and cyanidin glycosides. The highest concentration of cyanidin glycosides (a type of anthocyanin with antioxidant properties) is found in the peel of red pears.³ The phenolic acids found in pears — chlorogenic acid, ferulic acid, and citric acid — also contribute to pear’s health benefits. Both ferulic and chlorogenic acid are being studied for their ability to inhibit α-glucosidase and α-amylase, which appear to delay the digestion and absorption of carbohydrates.³ Ferulic acid is a potent antioxidant with a range of anti-inflammatory, anti-atherogenic, anti-diabetic, neuroprotective, and hepatoprotective effects. The citric acid content of some pear cultivars is considered high for non-citrus fruits (more than 2 g/kg fresh fruit) and has been shown to improve dietary iron absorption by as much as 600%.³

Pear cultivars with greenish-yellow and red-blush peels typically are high in chlorogenic acid and arbutin.⁸ In humans, chlorogenic acid regulates the metabolism of fats and glucose in the body and therefore plays an important role in managing diabetes and cardiovascular disease (CVD), while arbutin has anti-hyperglycemic, anti-hyperlipidemic, and antioxidant properties and is involved in alcohol metabolism.³

Modern Research

Researchers have examined various pear parts and preparations including whole pear fruit, pear peel, pear pulp, pear pomace, or pear extracts.³ Studies published on pear generally are observational or animal. Most human clinical studies of pear do not exclusively focus on pear but also include apple consumption. Although apples and pears are closely related, further investigation is needed focusing solely on pear.

Metabolic Health Markers and Chronic Disease

Hypertension, dyslipidemia, abnormal blood glucose, and chronic inflammation result from metabolic abnormalities that contribute to the onset of conditions such as cardiovascular disease (CVD), type 2 diabetes mellitus (T2DM), and cancer.³ Fruit and vegetable consumption can drastically reduce the risk of CVD. For every 200 g/day intake of fruit and vegetable consumption, stroke risk has been shown to decrease by as much as 32%.³ Results from three prospective studies indicate that consumption of both apples and pears is associated with a lower risk of stroke and CVD. While the effects of pear consumption alone were not assessed in these studies, it is thought that the fiber and polyphenols in pear work synergistically to affect blood pressure, lipid profiles, body weight, inflammation, and oxidative stress.

Weight management is a critical part of correcting metabolic abnormalities and improving overall health. Fruits are low-energy-dense foods that induce satiety without increasing calorie intake.¹⁰ Pear fruit is a low-calorie, high-fiber snack that has been studied for its potential in promoting weight loss. Regular consumption of pears is associated with lower body weight and a 35% reduction in risk of becoming obese.⁶ In one randomized clinical trial, 49 overweight middle-aged women were randomly assigned to add three pears, three apples, or three oat (Avena sativa, Poaceae) cookies to their regular diet. Participants who consumed pears or apples experienced significantly more weight loss compared to those who consumed oat cookies after 10 weeks.¹⁰ Since the fiber content of the oat cookie, pear, and apple was similar, researchers attributed the weight loss to the low energy density of pears and the overall reduction in daily caloric intake even though more food was consumed by weight.^3,10

T2DM, which is characterized by hyperglycemia and insulin resistance, is one of the fastest growing preventable chronic diseases in developed countries worldwide. There is consistent evidence from observational studies that daily pear and apple consumption is associated with a reduced incidence of T2DM. A cohort study by Muraki et al. found an inverse relationship between apple and pear consumption (collectively) and T2DM. An intake of more than one apple or pear daily correlated with a 17% reduction in T2DM risk.³ Additionally, participants who consumed three servings of juice made from whole pears and/or apples weekly showed a 14% lower risk of developing T2DM.^3,11 Similar research has found the strongest inverse association from intake of anthocyanin-rich foods (such as unpeeled pears and apples) and the risk of T2DM.^3,12 The peel of the pear fruit contains six to 20 times the antioxidant nutrients than the flesh. Additionally, studies have shown that removing the peel of the pear decreases the phenolic and vitamin C content of the fruit by 25%.¹³ Similar to other fruits and vegetables, consuming pears, peel and all, provide a complete array of its nutrients.¹³

Five out of the six published prospective and case-controlled studies on pears and apples have demonstrated that increased consumption of these fruits is associated with a reduced risk of certain types of cancer. A cohort study of more than 470,000 women and men across Europe found that both apple and pear consumption was associated with reductions in bladder cancer (each 25 g increment consumed resulted in a 7% risk reduction) and lung cancer (each 100 g increment consumed resulted in a 14% risk reduction).³ In addition, a study by Rossi et al. showed that for each portion of apple or Asian pear consumed, pancreatic cancer risk decreased by 27%.³ Pears contain ursolic acid, which inhibits aromatase activity, and its isoquercitrin helps maintain DNA integrity; these factors both play a role in cancer development.⁵ Additional studies are needed to further investigate pear’s potential cancer preventive properties and mechanisms.

Gastrointestinal Health

Both sorbitol and fructose are poorly absorbed in the small intestine and attract and move water into the large intestine, which softens the stool and elicits a laxative effect.³ Pear’s fructose and sorbitol content combined with its dietary fiber and pectin content gives the fruit the natural ability to prevent and treat constipation.³ Using pears to treat constipation may be especially useful in children who may be unaccustomed to taking medications or older adults who are often taking several medications.³ However, eating too many pears when not constipated may cause loose stools or diarrhea, especially in young children.¹³

Individuals with irritable bowel syndrome (IBS) often experience malabsorption issues as well as digestive discomfort upon eating foods high in fructose (e.g., honey, fruits, and corn [Zea mays, Poaceae] syrup); fructans such as inulin, which is found in wheat (Triticum aestivum, Poaceae) and onions (Allium cepa, Amaryllidaceae); and polyols such as sorbitol found in fruit and artificially sweetened foods. Due to their fructose and sorbitol content, pears should be avoided by those following a low FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) diet.^3,5

Hangover Helper

The key enzymes in alcohol metabolism are alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Consumption of high volumes of alcohol depletes these enzymes, which are needed to detoxify the body, and often results in a hangover. Symptoms of a hangover include headache, fatigue, diarrhea, dizziness, and poor concentration. Certain Asian populations have a genetic variation known as ALDH2, which is associated with a reduced, or inefficient, ability to metabolize alcohol.³ In an acute crossover randomized clinical trial, 14 healthy men consumed 220 mL of Asian pear juice or placebo (juice with fructose and pear flavoring) prior to consuming 540 mL of 20% alcohol. Participants that did not have the ALDH2 genetic variant in the pear juice group experienced significant alleviation of hangover symptoms. However, those who had the genetic variant did not experience alleviation from hangover symptoms when consuming pear juice prior to alcohol consumption.¹⁴ By adding fructose to the placebo drink, it was ruled out as a possible active ingredient. Research has confirmed that arbutin is the primary constituent responsible for stimulating ADH and ALDH activity and reduces the occurrence or severity of hangovers.³ Future larger studies including populations from other ethnicities need to be conducted to confirm these findings and assess the impact of different ethnic backgrounds.¹⁴

Allergic and Respiratory Conditions

Pears are considered a low allergenic food and are often one of the earliest foods introduced to infants.^3,4 In a cross-sectional study of 244 eight-year-old children who were sensitive to food-based allergens, there was an inverse association between pear and apple intake and allergic symptoms, including rhinitis, asthma, and chronic skin conditions like eczema.³ Pears are rich in quercetin and rutin, which down-regulate mast cell activity, reducing the severity of immune response to allergens.³ Clinical research is necessary before recommendations can be made regarding pear consumption as a dietary treatment for allergic and respiratory conditions.

Consumer Considerations

Peak season for pears is late summer to early autumn.³ Root cellars are used to store and slowly ripen immature European pears after harvest, which allows a longer period of consumer access to these late-season fruits. Pears are eaten fresh or cooked, canned, preserved as jams, juiced, dried, or fermented into hard pear cider.^2,3 Of the pears grown in the United States, only 60% are available to consumers in whole fruit form, while 40% of pears are processed into prepared foods or canned. When selecting fresh pears, one should choose fruits that slightly yield to pressure, like an avocado.^4,13 Unripe pears will ripen if stored at room temperature or, temporarily, in a brown paper bag. Once ripe, pears should be stored in the refrigerator away from strong-smelling foods, as pears tend to absorb odors.⁴

Fruits and vegetables that have thin skins are prone to pesticide residue accumulation. Pears, with their thin, phytonutrient-rich skins, are listed among the top 12 fruits and vegetables that have the highest pesticide residues, according to the “2018 Shopper’s Guide to Pesticides in Produce” published by the consumer advocacy organization known as the Environmental Working Group.¹⁵ According to the organization’s 2018 data, 48% of conventionally grown pears were shown to have an average of five detectable pesticides. Since 2010, the amount of pesticide residues on pears has more than doubled from 0.6 ppm to 1.4 ppm. Due to the cumulative nature of fat-soluble pesticide residues within the human body, it is important to wash produce in a diluted vinegar solution (three parts water to one part vinegar) to help remove pesticide residues.⁴ For infants, the elderly, or those with chronic illnesses, purchasing and consuming organically grown pears and pear products is strongly recommended.

Nutrient Profile¹⁶

Macronutrient Profile: (Per 1 small European pear [approx. 148 g])

84 calories
0.53 g protein
22.5 g carbohydrate
0.21 g fat

Secondary Metabolites: (Per 1 small European pear [approx. 148 g])

Very good source of:

Dietary Fiber: 4.6 g (15.3% DV)

Good source of:

Vitamin C: 6.4 mg (7% DV)
Vitamin K: 6.5 mcg (5.4% DV)
Folate: 10 mcg (2.5% DV)

Also provides:

Potassium: 172 mg (3.7% DV)
Riboflavin: 0.04 mg (3.1% DV)
Manganese: 0.07 mg (3% DV)
Magnesium: 10 mg (2.4% DV)
Vitamin B₆: 0.04 mg (2.4% DV)
Thiamin: 0.02 mg (1.7% DV)
Iron: 0.27 mg (1.5% DV)
Niacin: 0.24 mg (1.5% DV)
Phosphorus: 18 mg (1.4% DV)
Vitamin E: 0.18 mg (1.2% DV)
Calcium: 13 mg (1% DV)

Provides trace amounts:

Vitamin A: 37 IU (0.7% DV)

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

Image credits (top to bottom):

European pear tree flowers. Image courtesy of Sten Porse.
Pear illustration by Prof. Dr. Otto Wilhelm Thomé from Flora von Deutschland, Österreich und der Schweiz. 1885.
Asian pear fruit on the tree. Image courtesy of Wikimedia Commons.
European pear fruit. Image courtesy of Rasbak.
Hangover stock image courtesy of Michal Jarmoluk.

References

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2. New World Encyclopedia. Pear. New World Encyclopedia website. Available at: http://www.newworldencyclopedia.org/entry/Pear. Accessed on 12-5-18.
3. James-Martin G, Williams G, Stonehouse W, O’Callaghan N, Noakes M. Health and nutritional properties of pears (Pyrus): a literature review. Adelaide, Australia: Commonwealth Scientific and Industrial Research Organization; 2015.
4. Murray M. The Encyclopedia of Healing Foods. New York, NY: Atria Books; 2005.
5. Parle M, Arzoo. Why is Pear So Dear? International Journal of Research in Ayurveda and Pharmacy. Jan.-Feb 2016:7(Suppl 1);108-113.
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7. Soluble and Insoluble Fiber. MedlinePlus website. Available at: https://medlineplus.gov/ency/article/002136.htm. Accessed December 7, 2018.
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15. The Dirty Dozen. Shopper’s Guide to Pesticides in Produce. Environmental Working Group website. Available at: www.ewg.org/foodnews/dirty-dozen.php. Accessed on December 10, 2018.
16. Agricultural Research Service. Basic Report: 09252, Pears, raw. National Nutrient Database for Standard Reference Legacy Release. April 2018. United States Department of Agriculture website. Available at: https://ndb.nal.usda.gov/ndb/foods/show/09252. Accessed December 12, 2018.
17. Quessenberry S. Arugula and Pear Salad with Maple Vinaigrette. Real Simple website. December 2005. Available at: www.realsimple.com/food-recipes/browse-all-recipes/arugula-pear-salad-maple-vinaigrette. Accessed December 12, 2018.
18. Bauman H, Brown Z. Food as Medicine: Mustard (Brassica juncea and B. nigra, Brassicaceae). HerbalEGram. 2017;14(3). Available at: http://cms.herbalgram.org/heg/volume14/03March/FAMMustard.html. Accessed December 17, 2018.
19. Bauman H, Kwon M. Food as Medicine: Arugula (Eruca sativa, Brassicaceae). HerbalEGram. 2016;13(4). Available at: http://cms.herbalgram.org/heg/volume13/04April/FoodAsMedicine_Arugula.html. Accessed December 17, 2018.