HerbalEGram: Volume 17, Issue 10, October 2020

Editor’s note: Every other month, HerbalEGram highlights a conventional food and briefly explores its history, traditional uses, nutritional profile, and modern medical 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, and HerbalGram Associate Editor Hannah Bauman for their contributions to this project.

By Jenny Perez, ABC Education Coordinator

Overview

The cashew (Anacardium occidentale) belongs to the sumac family (Anacardiaceae), a tropical and subtropical plant family known for caustic resins that can cause allergic reactions. Members of this plant family, including poison ivy (Toxicodendron radicans) and poison sumac (T. vernix), have resin ducts in the bark which exude gums and resins that become black when exposed to air.¹ In addition to the cashew plant, other economically important fruits and nuts in the sumac family include mango (Mangifera indica), sumac berry (Rhus spp.) and pistachio (Pistacia vera).¹

The cashew is an evergreen tree with an irregularly shaped trunk and twisted, crooked branches that can grow to a height of 40 feet.^2-4 Cashew trees can thrive in the tropical climates of Central and South America, where soils are thin and humidity is high.^2,3 Its leathery leaves have smooth margins and are two to eight inches long, up to six inches wide, elliptical in shape, and spirally arranged around the stem.^2,3 The tree produces 10-inch long panicles (multi-branched infloresences) of seven-petaled, small fragrant flowers that change from pale green to a coppery-pink color after pollination has occured.^3,4 The true fruit of the tree is the one-inch-long, kidney-shaped, nut-like fruit, commercially known as the cashew nut.^3,5

The cashew “apple,” which more closely resembles a pear (Pyrus spp., Rosaceae) in shape, is an accessory fruit, or false fruit (pseudofruit), that develops from the receptacle of the flower rather than the flower itself.^3,4 It is reddish or yellow in color and grows up to four inches — three times the size of the cashew nut, or true fruit. ^2,3 The true fruit of the cashew tree is a drupe that grows at the end of the pseudofruit and consists of two walls or shells. The outer shell is smooth, thin, and elastic, and changes in color from olive green to pale brown when ripe.^2,3 Within the drupe is a single seed: the cashew nut.³ The seed is surrounded by a double shell containing a mixture of anacardic acids, which are closely related to urushiol (the caustic oily mixture exuded by poison ivy).³

Historical and Commercial Uses

The cashew tree is called maranon in most Spanish-speaking countries, but known as merey in Venezuela.⁵ In northeastern Brazil, the cashew tree is regionally known as cajueiro and the fruit is called caju, which is derived from what indigenous peoples called acaju or acajous (“to pucker the mouth”), referring to the astringent flavor of the fruit.^3,4 During the late 16th century, Portuguese traders brought the cashew plant to eastern Africa and India, where it thrived in nutrient-deficient sandy soils and was used as a fast-growing soil retainer near the seacoast.^2,4,5 Once naturalized, cashew trees were extremely hardy and drought tolerant, living 30 to 40 years in the extreme tropical heat of these regions.^4-6 When the low-growing, gnarled branches of the cashew tree rest upon the ground, they take root and can form extensive forests in the tropical lowlands of northern South America, Central America and the West Indies.^4,5

Cashew trees are economically important, and their components have numerous uses. The wood from cashew trees can be used for shipping crates, boats, and charcoal.⁵ The rough bark contains resin, acrid sap, and a gum similar to gum arabic (Senegalia senegal, Fabaceae).^4,5 Untreated wood from the cashew tree may cause allergic reactions and must be handled with care by susceptible individuals.² Resins from the unprocessed cashew seed are commercially known as cashew nut seed liquid (CNSL) and are considered an important agricultural byproduct of cashew production.³ CNSL is used as an insecticide, wood varnish, industrial sealant, laminating resin, epoxy resin, rubber compounding resin, and in cashew cement and other industrial applications.^2,3 The caustic, acrid-tasting resin present between the inner and outer cashew shell is used topically as a traditional medicine to remove corns and warts.⁵

In the international tree nut trade, cashew ranks third in global sales, with more than 20% of the market, and it is considered the second-most-expensive nut traded in the United Sates, after macadamia (Macadamia spp., Proteaceae) nuts.^6,7 Cashew processing and exportation began in the 1950s in India, and consumer demand has steadily increased.⁶ Cashews are produced in 32 countries with tropical and subtropical climates. According to published Food and Agriculture Organization (FAO) data, in 2005, the three major cashew-producing countries were India, Brazil, and Indonesia, followed by Vietnam and Nigeria.^2,3,5 Global annual production was reported to be 2.7 million tons.³

Cashew nut kernels are not true nuts and must be carefully processed before consuming. Processing involves several labor-intensive steps and must be undertaken with care due to the brown, oily resin composed mainly of anacardic acids in the nut shell that can blister human skin.^2,6 First, the nuts are removed from the cashew apple and then baked to loosen the inner and outer shells. This process often takes place in a roasting cylinder to avoid exposure to and inhalation of the caustic fumes caused by the burning resin. The shells are then removed by hand to harvest the edible seed inside.^2,3,7 Processing cashew nuts is somewhat hazardous, and workers must wear gloves to avoid painful skin rashes.^3,6

The thin, reddish-brown seed coat of the cashew, which contains 25% tannins, is difficult to remove, causes astringent, tingling sensations in the mouth, and generally is not desired by consumers.^6,7 Cashews that are whole, white, and without a seed coat (sold as “raw”) are considered high quality.⁶ Unfortunately, the removal of the seed coat also removes potent antioxidants, catechin and epicatechin, which are only present in the seed coat.⁷ More recent cashew-processing techniques enable the removal of the caustic CNSL while leaving the cashew skins intact, which increases levels of phenolic compounds compared to skinless cashew products.⁶

Cashew nuts are rich in oils and versatile in use, providing a distinct flavor in numerous chicken and vegetarian dishes of southern India and Asia. In Chinese cooking, cashews are often added to stir fries.⁴ In Western countries, cashews are consumed as a protein-rich snack food.² Cashew nuts can be easily ground into a spread similar to peanut (Arachis hypogaea, Fabaceae) butter.^2,4

The fragile cashew apple must be hand-picked and the curved fruits detached before being sun-dried.² Due to the hazards of processing the cashew nut, Latin Americans and West Indians commonly discard the nut and enjoy the juicy cashew apple instead. Cashew apples are highly perishable due to their susceptibility to various yeast and fungi post-harvest.^3,5 The juicy, acidic pulp of cashew apples is consumed fresh or used in beverages, jellies, and chutneys.² Cashew apple juice is very astringent and contains over 30% tannins.⁵ In Cuba and Brazil, cashew apple juice was prescribed as a remedy for sore throats and chronic dysentery.⁵

In Brazil, the pulp is fermented to make a vinegar called anacard, the juice is consumed diluted and sweetened as a refreshing beverage known as cajuina, distilled into liquor, or fermented into a Madeira-like wine known as cajuada.^3,4 Similarly, in Goa, India, the juicy pulp of the cashew apple is used to prepare fenny, a regionally popular distilled liquor. In Nicaragua, cashew apples are consumed fresh, made into juice, and used to create sweets, jellies, wine, and vinegar.⁵ Despite the versatility of the cashew apple, in many parts of the world, the cashew apple is discarded after the nut is removed because of its short shelf life.³

Nutrients and Phytochemicals

Nuts can help manage blood cholesterol levels, which is an important component of cardiovascular health.⁸ Cashew nut kernels are nutrient and calorie dense. They contain protein, cholesterol, more carbohydrates than other nuts (with the exception of pistachios), and are high in fat, most of which is unsaturated.⁴ Its high energy and protein content are ideal for growing children, pregnant and nursing mothers, and those recovering from illness.⁷

Cashews, along with almonds (Prunus dulcis, Rosaceae) and pistachios, have the highest protein of all tree nuts.⁶ The predominant amino acid is arginine, which plays a role in the vasodilation of blood vessels.⁶ Despite cashew nut’s high protein content, its biological value (BV), or protein bioavailability, is low due to the limited content of essential amino acids, especially lysine.⁶ Since essential amino acids represent the bottleneck in protein production in the human body, protein sources with low quantities of essential amino acids have a lower BV.

The most abundant vitamin in cashew nuts is vitamin E (α- and γ-tocopherols), which protects unsaturated fatty acids from becoming damaged through oxidation.^6,8 Cashews contain one of the highest levels of vitamin K of all nuts, an important vitamin for bone health and immunity.⁶ Like most nuts, cashews are rich in minerals, including potassium, magnesium, and calcium, all of which are important for maintaining bone health, heart health, and many other important body functions.⁷ Levels of phosphorus, potassium, and magnesium are high enough to substantiate US Food and Drug Administration (FDA)-approved nutrition label claims.⁶ Cashew nuts also contain copper, iron, and zinc.⁷

Foods containing high levels of monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) are associated with a lower risk of cardiovascular disease (CVD).^6,9 There is growing evidence that replacing refined grains with healthy fats, such as MUFAs, may improve high-density lipoprotein (HDL) cholesterol levels.¹⁰ This is important since just a 1% increase in HDL cholesterol levels is associated with a 3% reduction in CVD risk. However, cashew nuts also contain 20% saturated fat and deliver four grams of saturated fat per 50-gram serving.⁹ This excludes cashews from being officially listed by the FDA as a food associated with reducing risk of CVD.

Recent studies suggest that stearic acid, one of the most abundant saturated fats in cashews, has a neutral effect when used to replace carbohydrates or cholesterol-raising saturated fatty acids (SFAs), despite the widespread misconception that all high-calorie, high-fat snacks result in increased cholesterol levels and, potentially, weight gain.¹¹ Additionally, cashew nuts also contain other heart-healthy components such as glutamic acid, arginine, cholesterol-lowering phytosterols, and a variety of phenolic compounds (Table 1).^6,8 Cashews also contain significant levels of phosphatidylcholine, a phospholipid that improves cell membrane integrity and precursor to acetylcholine, the main neurotransmitter involved with muscle movements, memory, and circadian rhythms.⁷

Table 1. Primary Bioactive Compounds Present in Cashew Nut^6-8

Modern Research and Potential Health Benefits

The dietary role of nuts is considered vital to human nutrition. Nut-producing trees are perennial edible crops and reliably yield significant amounts of nutrient- and energy-dense nuts for decades once the tree matures. Similar to other tree nuts, cashew kernels have been studied primarily for their cardiovascular and metabolic health benefits.

Cardiovascular Effects

CVD is the leading cause of death globally, accounting for more than four million deaths annually in Europe and nearly 930,000 deaths annually in the United States.¹¹ In epidemiological studies, the consumption of tree nuts in the diet is associated with a reduced risk of CVD. While not a true tree nut, the cashew nut has similar characteristics nutritionally and phytochemically that validate its benefits as a nutrient-dense part of healthy diets.

In a randomized, crossover, isocaloric, controlled-feeding study, 51 men and women with median low-density lipoprotein (LDL) concentrations of 159 mg/dL at screening participated in two 28-day intervention periods with a two-week washout period between interventions.⁹ During each intervention, participants consumed either 28-64 grams daily of roasted salted cashews or baked potato (Solanum tuberosum, Solanaceae) chips, both providing 11% of daily total calories. Otherwise, participant diets were designed to reflect that of a typical US adult (49% carbohydrates, 16% protein, 33% fat). MUFA intake increased in the cashew group without affecting SFAs and PUFAs. Study results indicate that the cashew group had significantly decreased LDL cholesterol and total cholesterol levels compared with the potato chip group and no significant changes in triglyceride or HDL cholesterol levels. However, the cashew group also reported more adverse events. Of the 14 adverse events reported, eight were classified as possibly or probably related to consuming cashews and included constipation, bloating, increase in pain from pre-existing inflammatory conditions like arthritis and gout, weight gain, fatigue, and general malaise.

Some clinical trials indicate that cashew supplementation may have further drawbacks. In a similar randomized crossover trial, 42 individuals participated in a controlled-feeding study with two treatment phases.¹¹ The same diet was provided in both phases with no additions during the control phase and a 42-gram daily addition of cashews during the cashew nut phase. Diet and calorie intake were adjusted to achieve similar caloric intake of overall diets in both phases. After four weeks, CVD risk factors were measured, but there were no significant differences in blood lipids, blood pressure, augmentation index (an indicator of arterial stiffness), blood glucose, endothelin, adhesion molecules, or clotting factors. In fact, participants consuming the baseline diet with the addition of cashews experienced a significant increase in tumor necrosis factor-α (TNF-α) levels compared to those only consuming baseline diet, which indicates that cashew consumption may be associated with increased inflammation in the body. Cashew consumption was also associated with a decreased concentration of proprotein convertase subtilisin/kexin type 9 (PCSK9), which is associated with improved removal of LDL cholesterol from the bloodstream.

Metabolic Effects

Evidence suggests that consuming 60 grams of nuts daily may reduce fasting blood glucose and glycosylated hemoglobin A1c (HbA1c).¹⁰ These attributes are crucial to diabetes management and cardiovascular health. A recent meta-analysis of clinical trials indicates that despite the high calorie and fat content of nuts, long-term nut consumption is not associated with significant effects on body weight when included in a healthy diet, and is in fact associated with a lower risk of obesity.^7,10 Possible mechanisms that may explain this outcome include the thermogenic effects of readily oxidizable MUFAs and PUFAs, incomplete nut mastication resulting in lost calories via stool elimination, and enhanced satiety that results in less-frequent snacking.¹⁰

In a parallel-arm, RCT study, adults with type 2 diabetes with low HDL as well as dyslipidemia consumed their normal diet with or without 30 grams of raw cashews daily for 12 weeks.¹⁰ Those consuming the cashew nuts did so mid-morning or as an evening snack, not as a cooking ingredient. No other type of nut was consumed. Participants met with dietitians six times during the 12-week period to complete diet recalls, including a single 24-hour recall at baseline for participants in both groups. At the end of the study, those in the cashew group had a significant reduction in systolic blood pressure compared to the those in the control group. HDL levels were significantly improved from baseline, but there were no significant reductions in LDL cholesterol or other blood lipid markers.^10,11 Despite the significant increase in daily caloric intake by those in the cashew group, participants did not experience an increase in weight, body mass index (BMI), or waist circumference.

Consumer Considerations

Globally, cashews are one of the most popular tree nuts⁷ and have clinically supported cardiovascular benefits when added to typical American diet.⁹ Cashew oil can be extracted from the seed and used for culinary purposes.³ Although less frequent than tree nut allergies, cashews can cause allergic reactions in some individuals.³

Epidemiological evidence indicates that more than 170 foods can cause immunoglobulin E (IgE)-mediated allergic reactions.⁸ Cashew proteins are associated with potent allergic reactions. Anacardein is the main soluble protein in cashews (accounting for 40-45% of the total soluble proteins in cashew nuts) and is believed to be the main trigger for hypersensitivity reactions when consumed.⁷ Cashew nuts can cause two distinct hypersensitivity reactions: contact dermatitis (linked to cardol and anacardic acid present in CNSL) and IgE-mediated food allergy. Reactions can range from atopic dermatitis to fatal systemic allergic reactions.⁷ Approximately 20% of patients with type 1 hypersensitivity to cashew nut experience anaphylaxis.⁷ Reports reveal that cashew nut allergy is most common in young children (< four years old) and adult females.⁸

Consumers should be aware that cashew nut powder is often added to chocolate (from Theobroma cacao, Malvaceae) and milk-based products.⁷ Recent research indicates that the powdered milk used in manufacturing milk chocolate powder can contain approximately 25% roasted cashew kernel.⁸ Moreover, cashew processing treatments such as autoclaving, blanching, frying, and microwave heating have no effect on cashew nut allergens.⁸

Nutrient Profile¹²

Macronutrient Profile: (Per one ounce raw cashews)

157 calories
5 g protein
9 g carbohydrate
12 g fat

Micronutrient Profile: (Per one ounce raw cashews)

Excellent source of:

Copper: 0.62 mg (41% DV)
Zinc: 1.64 mg (20.5% DV women; 15% DV men)
Manganese: 0.47 mg (20.4% DV)

Very good source of:

Magnesium: 82.8 mg (19.7% DV)
Phosphorus: 168 mg (13.4% DV)
Iron: 1.89 mg (10.5% DV)
Selenium: 5.64 mcg (10.3% DV)

Good source of:

Vitamin K: 9.67 mcg (8% DV)
Vitamin B₆: 0.12 mg (7% DV)

Also provides:

Potassium: 187 mg (4% DV)
Dietary Fiber: 0.94 g (3% DV)
Niacin: 0.30 mg (2% DV)
Folate: 7.1 mcg (1.8% DV)
Vitamin E: 0.25 mg (1.7% DV)
Riboflavin: 0.02 mg (1.5% DV)

Trace amounts:

Calcium: 10.5 mg (0.8% DV)
Vitamin C: 0.14 mg (0.2% DV)
Thiamin: 0.12 mg (0.1% 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):

Anacardium occidentale. ©2020 Steven Foster
First known illustration of a cashew tree by André Thevet. 1558.
Anacardium occidentale. ©2020 Steven Foster
Anacardium occidentale. ©2020 Steven Foster
Anacardium occidentale. ©2020 Steven Foster

References

1. Anacardiaceae. Encyclopedia Britannica. Available at: www.britannica.com/plant/Anacardiaceae. Accessed on September 21, 2020.
2. Cashew. Encyclopedia Britannica. Available at: www.britannica.com/plant/cashew#ref194103. Accessed on September 21, 2020.
3. Cashew. New World Encyclopedia. Available at: www.newworldencyclopedia.org/entry/Cashew. Accessed on September 21, 2020.
4. National Geographic Society. Edible: An Illustrated Guide to the World’s Food Plants. Lane Cove, Australia: Global Book Publishing; 2008.
5. Morton J. Cashew apple. Fruits of Warm Climates. Available at: www.hort.purdue.edu/newcrop/morton/cashew_apple.html. Accessed on September 22, 2020.
6. Griffin L, Dean L. Nutrient composition of raw, dry-roasted, and skin-on cashew nuts. Journal of Food Research. 2017;6(6)13-28.
7. Kluczkovski A, Martins M. Cashew nut. In: Caballero B, Finglas P, Toldra F, eds. Encyclopedia of Food and Health. Manaus, Brazil: Federal University of Amazonus; 2016:683-686.
8. Tufail T, Saeed F, Ain H, et al. Cashew nut allergy; immune health challenge. Trends in Food Science & Technology. 2019;86:209-216.
9. Mah E, Schulz J, Kaden V, et al. Cashew consumption reduces total and LDL cholesterol: A randomized, crossover, controlled-feeding trial. American Journal of Clinical Nutrition. 2017;105:1070-1078.
10. Mohan V, Gayathri R, Jaacks L, et al. Cashew nut consumption increases HDL cholesterol and reduces systolic blood pressure in Asian Indians with type 2 diabetes: A 12-week randomized controlled trial. The Journal of Nutrition. 2018;148:63-69.
11. Baer D, Novotny J. Consumption of cashew nuts does not influence blood lipids or other markers of cardiovascular disease in humans: A randomized controlled trial. American Journal of Clinical Nutrition. 2019;109:269-275.
12. Cashew nut. USDA Food Data Central. Available: https://fdc.nal.usda.gov/fdc-app.html#/food-details/170162/nutrients. Accessed on October 2, 2020.
13. Stir-fried vegetables with toasted cashews. Food and Wine. September 2012. Available at: www.foodandwine.com/recipes/stir-fried-vegetables-toasted-cashews. Accessed on October 2, 2020.
14. Bauman H, Darby S. Food as Medicine: Broccoli (Brassica oleracea, Brassicaceae). HerbalEGram. 2016;13(3). Available at: http://cms.herbalgram.org/heg/volume13/03March/FoodAsMedicine_Broccoli.html. Accessed October 5, 2020.