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 (TSU) in San Marcos and the
University of Texas (UT) 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 Mariam Alhadob
a HerbalGram Associate Editor
b ABC Dietetics
Intern (TSU, 2017)
Overview
Spinach (Spinacia
oleracea, Chenopodiaceae) is an
annual plant that grows up to 23 inches tall (60 cm).1 Spinach
plants produce an edible rosette and toothed, fleshy leaves. There are two main
types of spinach: crinkled savory-leaf spinach and smooth or flat-leaf spinach.2
Spinach leaves are fleshy, deep green, and rich in essential nutrients and
phytochemicals. Spinach requires deep and nitrogen-rich soil to grow, and
prefers a cool climate, with spring and autumn being optimal growth seasons for
the leaves.2,3 The hot weather of summer may cause the spinach to bolt
quickly, which causes the leaves to deteriorate.3 The plant produces
greenish-yellow flowers when ready to set seed.4
Spinach
is native to southwest Asia, in the area of present-day Iran.3
Spinach cultivation spread to China in 647 BCE, and spread across Europe by the
12th century CE. Now, spinach is cultivated throughout the world in temperate climate
zones. In the United States, California is the largest producer of spinach,
followed by Arizona and New Jersey. The annual per capita consumption of
spinach in the United States was estimated to be 1.7 pounds in 2014.5
Phytochemicals and Constituents
Spinach
is one of the most nutritious leafy vegetables, and ranks second behind kale (Brassica
oleracea var. acephela,
Brassicaceae) in total carotenoids and folate content.6
Spinach is high in protein and low in carbohydrates and fat.
The
plant is a nutrient-dense source of vitamins and minerals, and maintains its
nutritional value well after cooking. Spinach provides an array of B vitamins,
which are important for carbohydrate metabolism, the nervous system, and the
brain. Spinach contains other important minerals including calcium, magnesium,
zinc, and selenium, and is a significant source of potassium, copper, iodine,
and iron.7 It also contains abundant amounts of vitamins A, K, and
C.7
The
flavonoid, phenolic acid, and carotenoid content of spinach makes it a healthy,
therapeutic food. These compounds are effective at neutralizing free radicals
in the body and are able to protect the body from damage and disease by
reducing inflammation.
The
two major carotenoids present in spinach leaves are lutein and beta-carotene,8
and they compose more than 65% of the total carotenoids content. Lutein may
help prevent vision loss from age-related degenerative disorders such as
macular degeneration and cataracts.9 A yellow pigment, lutein is
found in high amounts in the retina and absorbs blue light emitted by back-lit
devices such as smart phones and computer screens. Other carotenoids in spinach
include violaxanthin and neoxanthin.8
The
carotenoids in spinach are very delicate and highly susceptible to degradation over
time. Post-harvest handling of spinach from field to freezer does alter the
phytochemical profile of the leaves. In one study, storing fresh spinach leaves
for 24 hours at 39°F (4°C) did not impact
the carotenoids content in fresh spinach.8 However, storing fresh
spinach for 72 hours at the same temperature resulted in a reduction of the
carotenoids content by almost 15%. Blanching fresh leaves for two minutes at
212°F (100°C) followed by
freezing effectively preserved the carotenoid content of spinach.
Historical and Commercial Uses
Historically,
spinach leaves have been used as a
laxative, diuretic, antidote against poison or infection, and as a treatment
for asthma and other breathing difficulties, sore throat, and kidney stones.1
Spinach also has potential effects
against hyperglycemia and inflammation. The seeds were used to control fever, to
address back pain, and as a diuretic. In the Indian traditional medicine, the
plant is known as palak and was used
to treat liver injury or infection and jaundice. Spinach was prescribed and
used in traditional Iranian medicine as an antidepressant.10 Due to
its high iron and chlorophyll content, spinach often is used as a therapeutic
food for patients with anemia.11
Spinach
leaves are available commercially fresh, frozen, or canned. Depending on the
spinach cultivar and method of preservation, the nutrients and phytochemical
profile of spinach may vary.2 Spinach leaves can be eaten fresh or
cooked. Several popular spinach-based dishes are said to be prepared “a la
Florentine,” supposedly in honor of Catherine de Medici (1519-1589), who was
born in Florence and introduced the vegetable to the French court upon her
marriage to King Henry II.12
Modern Research
There
are limited data regarding the effect of whole spinach leaves on diseases,
metabolic pathways, and conditions. Most of the available literature reports
the effects of leaf extracts or
specific isolated phytonutrient components.
Oxidative Damage and Inflammation
The
antioxidant content of spinach leaf, which contains high amounts of vitamins A
and C, suggests protective effects against damage from cellular oxidation. A
mouse study found that supplementation with 1,100 mg/kg per day of methanolic spinach
leaf extract significantly decreased radiation-induced lipid peroxidation in
the liver.13 This study further demonstrated that the leaf extract
decreased the negative impact of radiation on glutathione levels.
A
2017 rat study used a different methanolic spinach leaf extract with high
levels of lutein, luteolin, quercetin, and coumarin.14 High-performance
liquid chromatography analysis of the extract confirmed the presence of these
compounds in active amounts. The study reported that intraperitoneal injection
of the extract showed a protective anti-inflammatory effect in mice that were
given isoproterenol to induce a heart attack. Spinach extract intake led to
changes in activities of multiple enzymes, including paraoxonase, lecithin-cholesterol
acyltransferase, C-reactive protein, myeloperoxidase, and caspase-3.
Furthermore, the levels of pro-inflammatory cytokines in the heart tissue were significantly
lower in mice pretreated with spinach extract than the control group. These results
indicate the potential protective effects of spinach against inflammation and atherogenesis
(the formation of abnormal fatty masses in arterial walls) when used as a concentrated
leaf extract.
Cancer Chemoprevention
An in
vitro study demonstrated that neoxanthin significantly suppressed inflammation
and proliferation of prostate cancer cells.15 Additionally, in a
bacteria-based model, flavonoids found in spinach leaves showed anti-mutagenic
potential.16
A
study in mice reported that the antioxidants extracted from spinach leaves have
protective effects against benign epithelial tumors.17 The potential mechanism of action was linked
to the direct and indirect abilities of antioxidant compounds in spinach leaves
to act as free-radical scavengers that inhibit the progression of
carcinogenesis.
The abundant
glycolipids in spinach leaves were found to possess inhibitory effects against gastric
cancer cell and promyelocytic leukemia cell proliferation in vitro.18
These findings are considered positive, but preliminary, results of the
potential therapeutic effects of spinach glycolipids to prevent cancer proliferation.
Cardiovascular Disease
In a
semi-randomized crossover study in humans, the consumption of a fortified
spinach beverage resulted in a
significant increase in plasma nitrate concentration, which correlated with
lower diastolic blood pressure within 150 minutes post-consumption and persisted
for five hours thereafter.19 This study suggests the possible
therapeutic uses of spinach as a safe alternative and effective carrier for
nitrate medications.
Supplementation
Spinach,
like most dark, leafy greens, contains a high amount of folate: 100 grams of
raw spinach provides almost half of an average person’s daily recommended
intake.7 Daily intake of spinach for three weeks showed a
significant increase in plasma folate concentrations, and processing spinach
leaves did not affect the bioavailability of folate when compared to fresh
whole-leaf spinach.20 Frozen whole-leaf spinach, minced spinach, and
liquefied spinach have similar effects in terms of increasing plasma folate
concentration.
Researchers
currently are examining the potential benefits of fortifying flour with
dehydrated spinach, with a goal to improve total folate content in bread.21
Fortification of white bread and whole grain bread with spinach (40 g spinach
per 100 g of other ingredients) increased the total folate content, despite the
effect of processing factors such as kneading and baking.
Diabetes
Spinach
leaves contain many beneficial compounds such as vitamin C, iron, zinc, folic
acid, polyphenols, and fatty acids. These compounds have protective effects
topically as well as internally.22 In a study, diabetic rats were
fed an aqueous spinach leaf extract to determine its effects on wound healing.
The results showed that the spinach group had better wound-healing outcomes as
indicated by significant improvements in epithelial and granulation tissue
formation and blood vessels. These results indicate the potential beneficial
effects of supplementation with spinach juice or other types of spinach
extracts to treat wounds and ulcers in patients with diabetes.
Consumer Considerations
In
August 2008, The US Food and Drug Administration (FDA) announced that it would
allow the irradiation of spinach in order to kill the harmful bacteria Escherichia coli and Salmonella after numerous outbreaks of
foodborne illness.23 Strains of E.
coli have the ability to survive and multiply in the absence of an animal
host when soil, water, and plants become contaminated. Pathogenic bacteria can grow
inside the leaf tissues of spinach, rendering typical antimicrobial surface
treatments ineffective. Uniformity of crop management practices as well as
environmental factors not only impact the vegetable quality, but also the
survival rate of E. coli in the soil
and on the leaf crops.24 There are concerns, however, about the
irradiation of food crops. Research indicates that the process generates
harmful reactive oxygen species and decreases the phytonutrient content of the
food in the process of eliminating foodborne pathogens.23
The
primary source of spinach leaf contamination with heavy metals is from
pesticides containing lead arsenate, environmental pollution, contaminated
irrigation water and rainwater, and runoff from nearby areas treated with plant
pesticides and fertilizers.25 Leaf crops are most sensitive to lead
contamination and bioaccumulation. Commercially farmed spinach is most
susceptible to heavy metal and pathogen contamination due to the reliance on
pesticides and poor land management techniques such as continual replanting in
contaminated soil.
Caution
with spinach consumption may be warranted in populations susceptible to kidney
stones. Spinach is one of a number of foods that naturally contains oxalates.3
The oxalate content in spinach is estimated to be about 0.77 mg/100 g. Oxalates
bind to many minerals, including calcium, zinc, and magnesium, inhibiting their
absorption.26 Approximately 80% of kidney stones contain calcium and
predominately consist of calcium oxalate.27 High levels of urinary
oxalate are a major risk factor and precursor to the formation of calcium
oxalate kidney stones. Observational data indicate an inverse relationship
between dietary calcium and the risk of kidney stone formation, since dietary
calcium may bind to oxalates in the gut, and thereby limit the absorption of
intestinal oxalates and subsequent excretion of urinary oxalates. However, a
study of three diverse populations noted only a small association between
oxalate and spinach consumption and the risk of kidney stone formation.27
Nutrient Profile7
Macronutrient Profile: (Per 100 grams raw
spinach)
23 calories
2.9 g
protein
3.6 g
carbohydrate
0.4 g
fat
Secondary Metabolites: (Per 100 grams raw
spinach)
Excellent source of:
Vitamin
K: 482.9 mcg (603.6% DV)
Vitamin
A: 9377 IU (187.5% DV)
Folate:
194 mcg (48.5% DV)
Vitamin
C: 28.1 mg (46.8% DV)
Manganese:
0.9 mg (45% DV)
Magnesium:
79 mg (19.8% DV)
Potassium:
558 mg (15.9% DV)
Iron:
2.7 mg (15% DV)
Very good source of:
Riboflavin:
0.19 mg (11.2% DV)
Vitamin
E: 2.03 mg (10.1% DV)
Vitamin
B6: 0.2 mg (10% DV)
Calcium:
99 mg (9.9% DV)
Dietary
Fiber: 2.2 g (8.8% DV)
Good source of:
Thiamin:
0.08 mg (5.3% DV)
Also provides:
Phosphorus:
49 mg (4.9% DV)
Niacin:
0.72 mg (3.6% DV)
DV =
Daily Value as established by the US Food and Drug Administration, based on a
2,000-calorie diet.
Recipe: Savory
Spinach-Onion Pastry
Courtesy of Mariam
Alhado
Ingredients:
- 3
cups frozen chopped spinach, thawed
- 1
yellow onion, thinly sliced
- 1/4
cup freshly-squeezed lemon juice
- 1 tablespoon
extra-virgin olive oil
- 1
tablespoon ground sumac or za’atar spice blend
- Salt
to taste
- 1
package frozen puff pastry
Directions:
- Heat
oven to 350°F. Using several layers of paper towels, squeeze as much excess
water from the frozen spinach as possible.
- In a
large bowl, combine spinach, onion, lemon juice, olive oil, sumac, and salt and
form a uniform mixture.
- Roll
out the pastry until it is smooth and of even thickness. Divide into three-inch
squares. Add a few tablespoons of the spinach mixture into the center of each
square, then fold the corners in and press to seal.
- Arrange
the pastries on a baking sheet and bake for 15-20 minutes, until golden brown
and heated through.
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