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.
The basic materials for this series were compiled
by dietetic interns from Texas State University in San Marcos and the
University of Texas at Austin through the American Botanical Council’s (ABC’s)
Dietetic Internship Program, led by ABC Education Coordinator Jenny Perez. We would like to acknowledge Perez, ABC Special
Projects Director Gayle Engels, and ABC Chief Science Officer Stefan Gafner,
PhD, for their contributions to this project.
By Hannah
Baumana and Erika Martinezb
a HerbalGram Associate Editor
b ABC Dietetics
Intern (Texas State, 2017)
Overview
The
pistachio (Pistacia vera) is the only
commercially grown species in its genus, which belongs to the Anacardiaceae family.
Members of the genus Pistacia are
among the oldest flowering nut trees and are small to medium in size, and
characterized by their ability to exude mastic (plant resin).1,2
Other economically important plants in Anacardiaceae include cashew (Anacardium occidentale) and mango
(Mangifera indica).
Pistachio
trees are temperate, deciduous trees adapted to the dry, hot, drought-prone
climates of the Middle East.1,2,3 The pistachio tree can grow to a
height of 10 meters (about 33 feet) and has pinnately compound leaves
containing three to seven leaflets.3,4 The trees are dioecious; both
male and female pistachio trees produce their own flowers.4 Female
trees are wind-pollinated and produce green and brown flowers with no petals during
the early summer.1,5 Female pistachio trees produce clusters of
nuts, botanically known as drupes, after being pollinated by a nearby male tree.1
The pistachio tree matures at a slow pace and typically bears fruit after seven
to 10 years.1,5
Similar
to almonds and other drupes, the pistachio fruit matures in clusters that
resemble grapes. Pistachio fruit has multiple parts: the nutmeat (kernel),
which is enclosed in a thin, hard shell (endocarp) surrounded by a fleshy hull
(mesocarp and exocarp).1 By the beginning of fall, the pistachio
nuts are ripe and their hulls begin to crack open, revealing the pistachio
kernels inside.5
Pistacia vera cultivars are
currently grown in many temperate parts of the world, including Mexico, Israel,
Australia, California, Italy, Greece, North Africa, and South Africa.3,4
In 2014, pistachio nuts represented 6% of the world’s total production of tree
nuts.2 Iran and California produce the majority of the global supply
of pistachio nuts.3 California, Arizona, and New
Mexico comprise all of the commercial pistachio production in the United
States, with California producing 99% of the total 312,000 acres planted.6
In 1976, the first commercial crop of pistachios in the United States was 1.5
million pounds and has dramatically increased to a record 2016 crop of more
than 900 million pounds.
Phytochemicals and Constituents
The
pistachio nut is nutrient-dense with less fat than other nut varieties. The nut
has a total fat content of 12.7 g per ounce, of which 1.5 g is saturated fat
(SF), 3.8 g is polyunsaturated fatty acids (PUFAs), and 6.7 g is monounsaturated
fatty acids (MUFAs).3 Oleic acid, a MUFA, and linoleic acid, a PUFA,
make up approximately 88% of the fatty acid profile. The high concentrations of
unsaturated fatty acids and low concentration of saturated fat in pistachios
may be associated with cardioprotective effects.3,7 The nut also
contains protein and all nine essential amino acids, which is of particular
importance for those who follow vegetarian and vegan diets.7
Moreover, pistachios are a good source of insoluble fiber, making up 80% of the
total fiber content per ounce.3
Pistachio’s
vitamin content includes fat-soluble vitamins A, C, E, and K, as well as many B
vitamins: thiamin (B1), riboflavin (B2),
niacin (B3), pantothenic acid (B5), and pyridoxine (B6).5,7
The thiamin content found in pistachios is relatively high.7 Pistachio
is a good source of vitamin K, which is necessary for good bone health.
Clinical studies have demonstrated that intake of vitamin K may result in
decreased incidences of type 2 diabetes mellitus, cancer, and cardiovascular
disease (CVD).
Pistachio
nut also provides an array of minerals including potassium, magnesium, calcium,
copper, manganese, zinc, and selenium.7 The potassium content in
pistachios may be helpful in stabilizing blood pressure in hypertensive
subjects, as maintaining a healthy sodium-potassium ratio can help offset the
hypertensive effects of sodium. Zinc and selenium are two important minerals
with distinct antioxidant properties that may play a role in reducing the
incidences of CVD and certain forms of cancer.
Researchers
have isolated and identified several bioactive compounds in pistachios
including cholesterol-lowering phytosterols, carotenoids, phenolic compounds,
and γ-tocopherol.7 In comparison with similar portions of other
nuts, pistachios contain higher amounts of phytosterols per one-ounce serving.3
These include in beta-sitosterol, stigmasterol, and campesterol.7,8 The
chemical structures of phytosterols resemble cholesterol, and they may
interfere with its absorption.3 Pistachio’s distinctive green color
is imparted by the carotenoids lutein and zeaxanthin; these carotenoids are
found in high concentrations within the retina, and dietary intake may help
protect the eye from oxidative damage and delay age-related vision degeneration.7,9
γ-tocopherol, a powerful antioxidant, targets reactive nitrogen species and may
reduce inflammation by inhibiting the activity of the enzyme cyclooxygenase-2 (COX-2).3
Pistachio
also contains phenolic compounds, including anthocyanins, proanthocyanidins,
gallic acid, ellagic acid, flavonoids, phenolic acids, and stilbenes.10
However, the majority of the phenolic compounds are more concentrated in the
inedible hulls than in the pistachio kernel.7
Historical and Commercial Uses
The
pistachio tree is native to central and southwest Asia.11 Archeological evidence suggests that
humans were consuming pistachios in what is now modern-day Turkey by 7,000 BCE,
and pistachio trees were cultivated in the gardens of Babylon under the rule of
King Merodach-Baladan II around 700 BCE.3 A legend about the Queen
of Sheba holds that she confiscated all of Assyria’s pistachio nuts for her
personal consumption, declaring them an exclusive royal delicacy.3,5
Couples in Persia would stand underneath pistachio trees by the moonlight in
order to listen to the sound of cracking pistachio shells, which was considered
a symbol of prosperity.5
By
the first century CE, Syrian trade introduced pistachios to the Romans,5
who transported pistachios throughout the Mediterranean and across the Asian
continent to China. By the 16th century, pistachios were introduced to England.
In 1854, the pistachio arrived in the United States as an experiment directed
by a seed supplier named Charles Mason, and in 1875, American botanist William
Whitehouse successfully cultivated pistachio from seed and developed the
“Kerman” variety in California.5,11,12 Kerman pistachio trees were
later commercially planted throughout California during the 1960s and early
1970s, where they remain a successful food crop.3
Consumption
of pistachio nuts has been mentioned as a traditional folk remedy in Jordanian
folk medicine to treat jaundice.5 They also were consumed in
traditional Iranian medicine to treat hepatic, renal, cardiovascular, and
respiratory diseases.12 Some evidence suggests that pistachios were consumed
to treat bruises, chest pain, circulatory disorders, rheumatism, and liver
sclerosis.13 Other records indicate that pistachios were
historically consumed to soothe tooth pain.14 In Assyria and Greece,
the pistachio was used as a powerful aphrodisiac and consumed as a remedy to
counteract the effects of animal venom.15
Other
parts of the pistachio tree were used traditionally, as well. Some European and
Middle Eastern countries used the resin from the trunk to stop heavy bleeding,
and in India, the pistachio shells were used in the making and processing of
hides.14 Iranians often use pistachio shells as compost and livestock
feed.11 The oil from the pistachio nut is utilized in Iran for the
manufacture of cosmetic products.
Currently,
pistachios are commercially harvested and processed, and available roasted,
salted or unsalted, and flavored.3 Pistachios often are used in
baked goods and as a flavoring for candies and ice cream.11
Pistachio nuts have also been gaining popularity as a source for nut butter.
The nut’s complete amino acid profile has made pistachio a popular addition to
vegan and vegetarian protein products such as powders, bars, and drink mixes.
Modern Research
The
pistachio nut can be considered an important part of a balanced diet due to its
nutritional profile. Emerging evidence suggests a correlation between the
bioactive compounds found in pistachio and the prevention of chronic health
conditions, including cardiovascular disease, diabetes, obesity, and cancer.
Cardiovascular Disease
A
prospective, randomized, crossover human clinical trial replaced 15% of total
fat calories in subjects’ diets with those provided by pistachio nuts.16
After four weeks, the subjects who consumed two to three ounces of pistachio
nuts daily had significantly improved ratios of total cholesterol to high
density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL)
cholesterol to HDL cholesterol, and B-100 to A-1 (proteins associated with
cholesterol levels) over baseline. Although the mechanism of action by which
pistachio nuts can improve serum lipid levels is still unclear, researchers hypothesize
that pistachio’s low saturated fat content, impressive mineral profile, and bioactive
compounds, such as phytosterols, may have played a role in the reduction of
cholesterol levels in the subjects.16
Diabetes
In a
randomized, controlled, crossover clinical trial, subjects diagnosed with
prediabetes who consumed two ounces (57 g) of pistachio nuts daily for a period
of four months displayed significant positive changes in LDL and HDL
cholesterol levels compared to those who consumed a nut-free diet. Researchers
also reported that subjects consuming the pistachio-supplemented diet displayed
significantly lower fasting glucose levels and improved insulin resistance.17
Researchers
hypothesized that the consumption of pistachios can potentially impact insulin
production by elevating the levels of glucagon-like peptide-1 (GLP-1), a
hormone present in the stomach.17 GLP-1 modulates insulin release
and inhibits the release of glucagon to stabilize glucose levels in the blood. The authors of this study found that the subjects who included pistachios in their
diets exhibited a significant decrease in inflammatory markers, including oxidized
LDL, fibrinogen, and platelet factor-4 (PF-4), when compared to control. The
favorable changes in inflammatory markers can be explained by the elevated
serum levels of lutein and γ-tocopherol (antioxidant substances found in high
amounts in pistachios) in the participants from the pistachio group. Further
studies are warranted specifically in the pre-diabetic population to validate a
correlation between pistachio consumption and blood glucose management.
Weight Management
A
randomized, isocaloric weight-loss trial compared weight loss and body mass
index (BMI) measurements in overweight and obese participants who consumed
either a serving of pistachios or a pretzel as a snack for a 12-week period.3
Although the participants from each group exhibited some level of weight loss,
those who consumed the pistachio snack had a significantly higher reduction in
body weight and BMI than the pretzel group. Furthermore, those in the pistachio
group had significant reductions in serum triglyceride levels compared to the pretzel
group. Researchers hypothesized that pistachio consumption increased feelings
of fullness by stimulating satiety cues.
Two
studies have investigated the correlation between consuming pistachios in the
shell versus shelled pistachios and the amount consumed. Both studies observed
that participants consumed fewer calories when presented with pistachios in the
shell, and researchers hypothesized that this result could be due to the visual
representation of the shells left on the table as participants consumed the
nuts. Researchers also noted that when participants had to take the time to
open the shells, it appeared that on average, participants reported a 40%
reduction in calories that would otherwise have been consumed if the
participants were provided with the pistachio nuts without their shells.3
Other Uses
Pistachio
leaves, resin, and all parts of the nut have traditional medicinal uses, and
modern in vitro studies suggest that these plant parts demonstrate
anti-inflammatory, antioxidant, anti-microbial, and photoprotective activities.12
Recently, researchers have focused on the potential therapeutic properties of
the pistachio hull and skin, both of which are often discarded byproducts of
the commercial pistachio industry.
When
compared to other parts of the pistachio tree, the hull has higher levels of
phenolic, antioxidant, and anti-mutagenic activity.12 Aqueous
extracts of the pistachio hull have been analyzed for their ability to induce
apoptosis (normal, pre-programmed cell death) as well as their cytoprotective
effects and ability to prevent cell membrane peroxidation of both red and white
blood cells.12,18 Pistachio hull extract is rich in flavonols (like
quercetin), phenolic acids (like gallic acid), and flavan-3-ols (like catechin),
and in vitro evidence has shown that pistachio hull extract can induce
apoptosis in HepG2 cells.
In
vitro research also suggests that pistachio skin and hull extracts have
photoprotective properties. Plant-derived phenols have been shown to exhibit
photo- or UV-protective activity when taken orally or applied topically. There
is evidence that anthocyanins, which accumulate in the pistachio skin in the
presence of strong sunlight, can function as efficient UV-absorbing agents.19
In addition to the antioxidant properties of phenolic compounds, they also
exhibit a significant anti-inflammatory effect. All of these factors support
its potential use as a low-cost ingredient with high added value in UV-protective
products.
Consumer Considerations
Studies
have demonstrated that levels of all antioxidant and phenolic compounds present
in pistachio nuts decrease when roasted, with the anthocyanin content being
most significantly reduced by these post-harvest practices.20 These
results indicate that the pistachio skin plays an important role in protecting
the seed/kernel from becoming oxidized and rancid. Consumers should purchase
raw pistachios in the shell in order to obtain the most nutrients from the nut.
Like other tree nuts, pistachio nut can induce
immunoglobulin E (IgE)-mediated allergic reactions in sensitized/allergic
individuals, especially due to its genetic relationship to cashew nut.2
In terms of clinical presentation, allergic reactions to pistachio are
typically immediate (within minutes after ingestion or contact) and can result
in moderate-to-severe clinical symptoms, which may include hives, rash, eczema,
lip swelling, vomiting, abdominal pain, nasal congestion, or hypotension.2
Another concern regarding consuming pistachio and
other tree nuts is the potential post-harvest contamination with mycotoxins or
aflatoxins. These are highly toxic secondary metabolites that are produced by Aspergillus fungal species common in
hot, humid climate conditions.2 The most commonly affected tree nuts
are almonds (Prunus dulcis, Rosaceae),
hazelnuts (Corylus americana,
Betulaceae), and pistachios. Aflatoxins are very resistant to the most common
food processing techniques and present a potentially serious threat to both
human and animal health. The maximum allowable amount of aflatoxin amounts on
pistachio, almond, or hazelnut is 8-10 µg/kg of daily dietary exposure.21
The United States’ strict standards for aflatoxin contamination have
significantly decreased consumer exposure to aflatoxins.
Nutrient Profile22
Macronutrient Profile: (Per 1 ounce raw
pistachios [approx. 49 kernels])
159 calories
5.7 g protein
7.7 g carbohydrate
12.9
g fat
Secondary Metabolites: (Per 1 ounce raw
pistachios [approx. 49 kernels])
Excellent source of:
Vitamin
E: 6.83 mg (45.5% DV)
Vitamin B6: 0.5 mg (29.4% DV)
Thiamin:
0.25 mg (20.8% DV)
Very good source of:
Manganese:
0.3 mg (13% DV)
Vitamin
A: 635 IU (12.7% DV)
Phosphorus:
139 mg (11.1% DV)
Dietary
Fiber: 3 g (10% DV)
Good source of:
Magnesium:
34 mg (8.1% DV)
Potassium:
291 mg (6.2% DV)
Iron:
1.1 mg (6.1% DV)
Also provides:
Riboflavin:
0.05 mg (3.9% DV)
Folate:
14 mcg (3.5% DV)
Vitamin
K: 3.7 mcg (3.1% DV)
Niacin:
0.4 mg (2.5% DV)
Calcium:
30 mg (2.3% DV)
Vitamin
C: 1.6 mg (1.8% DV)
DV =
Daily Value as established by the US Food and Drug Administration, based on a
2,000-calorie diet.
Recipe: Chickpea
and Pistachio Salad with Citrus Vinaigrette
Adapted from Cooking for 223 Ingredients:
- 3
tablespoons orange juice
- 3
tablespoons extra virgin olive oil
- 1
tablespoon lime juice
- 1
small garlic clove, minced
- 1/4
teaspoon ground cumin (Learn more about the benefits of cumin here.24)
- 1/8
teaspoon cayenne pepper
- 1
15-ounce can of chickpeas, drained and rinsed (Learn more about the benefits of
chickpea here.25)
- 3
radishes, thinly sliced
- One
carrot, shredded or finely chopped (Learn more about the benefits of carrot here.26)
- 2
green onions, thinly sliced
- 1/4
cup pistachios, chopped
- 1/3
cup chopped parsley
- 3
cups salad greens
Directions:
- Whisk
the first six ingredients together. Season with salt to taste.
- In a
medium bowl, combine dressing, chickpeas, radishes, carrot, green onions,
pistachios, and parsley and stir gently. Serve over salad greens.
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Image captions/credits (top to bottom): Pistacia vera nuts in the shell “Kerman” variety pistachio nuts at Springs Preserve in Las Vegas, Nevada; photo courtesy of Stan Shebs Shelled and blanched pistachio nuts
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ML. Pistachio nuts: Composition and potential health benefits. Nutr Rev. 2012.
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