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 Haley Royerb
a HerbalGram Associate Editor
b ABC Dietetics
Intern (Texas State, 2016)
Overview
Pecan
(Carya illinoinensis) is a member of
the Juglandaceae family, which also includes other economically important North
American trees, such as hickory (Carya spp.) and walnut (Juglans spp.).1,2 Fossil records show that the pecan
tree can live up to a thousand years, and its existence predates human
settlements in North America.3 Pecan can grow to a height of 150
feet with a seven-foot diameter.2-4 The deciduous, lanceolate leaves
are alternate and odd-pinnately compound, and are typically made up of 9-17
leaflets.4 In the spring, the tree produces both male and female
inconspicuous flowers that are often wind-pollinated.5,6 During the
summer, the “fruit” of the tree grows in clusters of 3-6 one-inch oblong
brown-shelled nuts, called endocarps, that contain two seeds that are referred
to and sold in the market as pecans.4,5
The
pecan tree initially requires well-drained soil with an adequate water supply;
however, once established, it is drought-tolerant.7 Pecan trees are
native to North America, and typically grow in the southern and midwestern
regions of the United States and in the northern regions of Mexico.2,8
Eighty percent of the world’s supply of pecans is grown and produced in the
United States,2 but other countries, such as Mexico, Brazil, Peru,
Israel, China, South Africa, and Australia also produce pecans on a large
commercial scale.4,7 In the
United States, pecans are grown and harvested commercially in 14 states. More
than 75% of US pecans come from Georgia, New Mexico, and Texas, which produced
76 million, 67 million, and 61 million pounds, respectively, in 2014.9,10
Among tree nut consumption in the United States, pecans
rank third behind almonds (Prunus dulcis,
Rosaceae) and English walnuts (Juglans
regia, Juglandaceae), respectively.10 In 2014, the global pecan crop
totaled 264.2 million pounds or 132,075 US tons and was valued at $517 million,
a 12% increase from 2013. In terms of pecan exports, Hong Kong and Vietnam
remain the primary markets for in-shell pecans from the United States. Canada
and the Netherlands are the primary markets for shelled pecans from the United States.
Phytochemicals and Constituents
Pecans
contain essential fatty acids, 17 different vitamins and minerals, and phenols
and phytosterols.4 They are calorie-dense and have a high fat
content.7 Of all culinary nuts (though the pecan nutmeat is
botanically considered a drupe), pecans have the second-highest fat content
after macadamia (Macadamia spp., Proteaceae).11
Pecans are low in saturated fats but are a rich source of monounsaturated fatty
acids (MUFAs), primarily oleic acid, and polyunsaturated fatty acids (PUFAs),
predominantly linoleic acid (omega-6).4 Diets with higher intakes of
MUFAs and PUFAs and lower intakes of saturated and trans fats correlate with a
lower risk for cardiovascular disease (CVD).
Compared to other nuts, pecans have an especially
high antioxidant content.12 Specifically, pecans contain bioactive
compounds such as phenols, condensed tannins (e.g., proanthocyanidins, or
PACs), hydrolyzable tannins (e.g., derivatives of gallic and ellagic acids),
and tocopherol isomers that contribute to their antioxidant activity.12,13
Phenolic acids, such as gallic acid, may inhibit
the growth of a variety of bacteria.14 PACs exhibit antimutagenic
properties and antioxidant effects,1 specifically by inhibiting
lipid oxidation in both foods and in human cells.15 A study that
analyzed phenolic compounds from 18 different pecan cultivars in the United
States found that the most abundant antioxidants present were PACs, as well as gallic
and ellagic acids and their derivatives.12
Pecan shells have also been tested for bioactive
compounds and reportedly contain higher amounts of phenolic compounds than the
actual pecan nutmeat.13 Current research is exploring the use of
teas prepared with pecan nut shells to treat liver damage in rat models, which
may expand the role of pecans in the human diet.16 However, no human
research has been conducted regarding the therapeutic use of pecan shells, so
additional research is warranted to ensure safety.
Pecans are an excellent source of tocopherols,
which are forms of lipid-soluble vitamin E, and exist as four different
isomers: alpha, beta, gamma, and delta.4 Foods
that are sources of vitamin E typically contain alpha-tocopherol
and gamma-tocopherol.
Pecans have unusually high gamma-tocopherol
content: around 25
mg of gamma-tocopherol per 100 grams. Gamma-tocopherol has been observed to act as a stronger antioxidant in
vivo than alpha-tocopherol.17 In addition, it has been suggested
that gamma-tocopherol may also detoxify reactive nitrogen oxide species, and
thus reduce inflammation in the body.
In addition, pecans contain phytosterols, also
known as plant sterols, primarily in the forms of beta-sitosterol and
stigmasterol, which may help lower cholesterol levels.12,18 In the
small intestine, phytosterols compete with cholesterol for absorption and thus
inhibit the body’s uptake and reuptake of cholesterol in the blood stream. This
can improve serum cholesterol levels and may reduce low-density lipoprotein (LDL)
cholesterol by up to 10-14%.4 Different cultivars and the degree of
ripening in pecans yield varying quantities of phytosterols, but all varieties
provide these plant sterols.19
Historical and Commercial Uses
The
word “pecan” likely comes from an Algonquian language. French traders recorded
the word as pacanes or pecanes, which later evolved into its current common name.8
Native Americans consumed and stored pecans, but also traded them for furs and
other goods.2 The low-water and high-calorie contents of pecans help
them survive long storage.20 A historical record from the mid-1500s
by the Spanish explorer Álvar Núñez Cabeza de Vaca revealed that Native
Americans in south Texas would gather pecans in autumn and then grind them and
soak them in water to make a milky beverage to sustain them throughout the
winter.4 This liquid also formed the base of a fermented beverage
called powcohicora. Native Americans
also used ground pecan meal to thicken stews, and roasted the pecans for
sustenance on long journeys.3
In
addition to using the pecan nuts as a food source, the Kiowa tribe of the Great
Plains area of the United States used decoctions of the tree bark to treat
tuberculosis.21 The Comanche Nation used a poultice of pulverized
pecan tree leaves as a topical treatment for ringworm-infected skin.
Although
it can be used as a source of wood,3 the pecan tree is primarily
grown and commercialized for its nuts. In order to reduce waste, different uses
for pecan shells are being researched more extensively. Pecan shell mulch is
available in areas that produce pecans commercially; however, its high tannin
content may inhibit the growth of certain plant species. In addition, pecan
shells can be used like wood chips to smoke and barbeque meats.
Due
to its wide distribution throughout the state and long history of cultivation,
the pecan tree became the official state tree of Texas in 1919.3 Texas
also officially recognized pecan as its state health nut in 2001, and named
pecan pie as the state pie in 2013.22
Modern Research
Currently,
most research conducted on pecan consists of epidemiological or
population-based studies that analyze correlations between nut consumption and
lowered risk of CVD.23 However, there have been some in vitro and
clinical research studies that have investigated the effects of pecan
consumption in regards to antioxidant capacity.
Cardiovascular Health
Nut
consumption has been linked to lowered risk of cardiovascular events such as
heart attacks.4,23 Epidemiological studies suggest a 37% decreased
risk for coronary heart disease when nuts are consumed at least four times a
week compared to infrequent or no nut consumption.24 A systematic
review and meta-analysis of 61 trials confirmed that increased intake of tree
nuts was associated with lower total cholesterol, LDL cholesterol, apolipoprotein
B (Apo B, the main protein constituent of LDL cholesterol), and triglyceride
levels.25 The review also found that nut consumption correlated with
markedly lower Apo B levels in patients with diabetes versus patients without
diabetes. Because people with diabetes are at an increased risk for CVD, this
finding is significant and should be explored further.
In a crossover
study, participants were randomly assigned to consume either a pecan-enriched
diet or the National Cholesterol Education Program Step 1 diet for four weeks. The
participants switched diets for the following four weeks. When consuming the
pecan-rich diet, participants demonstrated a decrease in concentrations of Apo
B and an increase in Apo A1, which stimulates an uptake of high-density
lipoprotein (HDL) cholesterol, beyond the values observed in the Step 1 diet.26
Decreased LDL and increased HDL cholesterol levels were also observed in
participants while consuming the pecan diet. In addition, the pecan-enriched
diet resulted in decreased plasma triglycerides.
A
study assessed postprandial (post-meal) plasma antioxidant capacity in human
subjects after pecan consumption, and found that participants who consumed 90
grams (about three servings) of whole pecans or pecans blended with water had
significantly higher hydrophilic and lipophilic plasma oxygen radical
absorbance capacity (ORAC; which measures antioxidant capability in blood),
decreased LDL oxidation, and increased plasma catechin concentrations, compared
to the control meal that matched the pecans in caloric, fluid, and
macronutrient contents.27 This demonstrates the bioavailability and
potential antioxidant action in humans after consuming pecans.
Similarly,
a randomized controlled, crossover trial assessed the impact of the addition of
pecans to the diet on cholesterol levels and antioxidant capacity. Twenty-four
healthy participants were assigned to either a control diet with no pecans or a
pecan-enriched diet for four weeks, and then switched diets for another four
weeks.15 The results showed that during the consumption of the
pecan-enriched diet, participants significantly increased serum gamma-tocopherol (normalized to total cholesterol) while decreasing
plasma LDL levels and inhibiting lipid peroxidation and degradation. Total
antioxidant activity was not significantly different between groups.
Type 2 Diabetes
Though
the mechanism of action is not fully understood, an inverse relationship has
been observed between nut consumption and risk for developing type 2 diabetes.28
The Nurse’s Health Study suggested that a higher intake of MUFAs and PUFAs may
contribute to improved insulin sensitivity.
For
individuals with type 2 diabetes, it appears that nut consumption has a neutral
impact on blood glucose and insulin levels.28 This makes nuts a
healthy option for people with diabetes looking to lower their risk of CVD
while having minimal impact on their blood glucose levels. Though the caloric
intake associated with adding nuts to the diet is a concern, especially for
those with, or at risk for, type 2 diabetes, the evidence that increased nut
intake is associated with weight gain is inconclusive. Some studies show slight
weight gain and others show weight maintenance or even loss with the addition
of nuts to a calorie-controlled diet.28,29
Consumer Considerations
Like
many other nuts, pecans contain phytic acid, which can block or reduce
absorption of important minerals, including calcium, magnesium, iron, and zinc.4
The process of soaking or drying the pecans prior to consumption can reduce the
phytic acid content. Pecans are also high in oxalates, so individuals with a
history of calcium oxalate kidney stones should consider limiting intake of
pecans to prevent complications.
Pecans
are in the class of tree nuts, which are fairly common food allergens. It is
estimated that about 1% of the population (about three million people) in the
United States suffers from tree nut and/or peanut (Arachis hypogaea, Fabaceae) allergies.4 These allergies can
cause severe reactions, such as life-threatening anaphylaxis. Individuals with
tree nut allergies should therefore avoid consumption of or exposure to pecans,
and always read food ingredient labels to determine if there is any possible
contamination from the processing facility.
Although
more common in peanuts and Brazil nuts (Bertholletia
excelsa, Lecythidaceae), nuts like pecans are susceptible to contamination
with a mold called Aspergillus flavus,
which produces aflatoxins, which are among the most carcinogenic substances
known, and also have the potential to lead to mental impairment in children.4
To avoid this mold, it is important to purchase high-quality nuts from
reputable grocery stores that keep them in a dry, cool environment. Because of
their high fat content, shelled pecans have a shorter shelf life than pecans in
the shell and become rancid easily, so it is best to consume them soon after
shelling or properly store them in the refrigerator or freezer.4,11
Purchasing them in the shell and roasting them at home can also safeguard
against this fungal growth.11
Nutrient Profile30
Macronutrient Profile: (Per 1 ounce
[approx. 28.4 grams])
196 calories
2.6 g protein
3.9 g carbohydrate
20.4 g fat
Secondary Metabolites: (Per 1 ounce
[approx. 28.4 grams])
Excellent source of:
Manganese: 1.3 mg (65% DV)
Vitamin E: 7.6 mg (36.7% DV)
Very good source of:
Thiamin:
0.2 mg (13.3% DV) Dietary
Fiber: 2.7 g (10.8% DV)
Good source of:
Magnesium:
34 mg (8.5% DV) Phosphorus:
79 mg (7.9% DV)
Also provides:
Iron:
0.7 mg (3.9% DV) Potassium:
116 mg (3.3% DV) Vitamin
B6: 0.06 mg (3% DV) Riboflavin:
0.04 mg (2.4% DV) Calcium:
20 mg (2% DV) Niacin:
0.3 mg (1.5% DV) Folate:
6 mcg (1.5% DV) Vitamin
K: 1 mcg (1.3% DV)
Trace amounts:
Vitamin
C: 0.3 mg (0.5% DV) Vitamin
A: 16 IU (0.3% DV)
DV =
Daily Value as established by the US Food and Drug Administration, based on a
2,000-calorie diet.
Recipe: Pecan Pie
Energy Bites
Courtesy of Gluten
Free Vegan Pantry31
Ingredients:
- 2
cups Medjool dates, pitted
- 1 1/2
cups pecans
- 1/2
cup rolled oats
- 1
teaspoon cinnamon
- 2
tablespoons maple syrup
Directions:
- Process
dates in a food processor on high for about 45 seconds, or until a date ball
begins to form.
- Add
pecans and process for another 1-2 minutes.
- Add
remaining ingredients, scraping down the sides of the processor bowl if
necessary, and process for another 1-2 minutes.
- Using
a small ice cream scoop or 1-tablespoon measure, portion out the mixture and
roll into balls. Place on a parchment paper-lined baking sheet and place in the
refrigerator for 15-20 minutes.
- Store
in an airtight container in the refrigerator for up to a week.
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Photo credits: Top: Pecans on the tree. Photo by Dobbi. Middle: Pecan specimens from the Museum de Toulouse. Photo by Roger Culos, via wikimedia commons. Bottom: Shelled pecans. Photo by Markus Brunner via wikimedia commons.
References
- Villarreal-Lozoya
JE, Lombardini L, Cisneros-Zevallos L. Phytochemical constituents and
antioxidant capacity of different pecan [Carya
illinoinensis (Wangenh.) K. Koch] cultivars. Food Chemistry.
2007;102:1241-1249.
- National Geographic
Society. Edible: An Illustrated Guide to
the World’s Food Plants. Lane Cove, Australia: Global Book Publishing;
2008.
- Pecan Tree: Texas
State Tree. State Symbols USA website. Available at: www.statesymbolsusa.org/symbol-official-item/texas/state-tree/pecan-tree.
Accessed October 16, 2017.
- Murray M. The Encyclopedia of Healing Foods. New
York, NY: Atria Books; 2005.
- Plants Profile for Carya illinoinensis (pecan). United
States Department of Agriculture website. Available at: http://plants.usda.gov/core/profile?symbol=cail2. Accessed October 16, 2017.
- Cheatham S,
Johnston MC, Marshall L. The Useful Wild
Plants of Texas, the Southeastern United States, the Southern Plains, and
Northern Mexico. Volume 3. Austin, TX: Useful Wild Plants, Inc; 2009.
- Van Wyk B-E. Food Plants of the World. Portland, OR:
Timber Press; 2006.
- Hall GD. Pecan food
potential in prehistoric North America. Economic
Botany. 2000;54(1):103-112.
- Lillywhite J,
Simonsen J, Heerema R. US consumer purchases and nutritional knowledge of
pecans. Horttechnology.
2014;24(2):222-230.
- Pecans.
Agricultural Marketing Resource Center website. August 2015. Available at: www.agmrc.org/commodities-products/nuts/pecans/.
Accessed October 16, 2017.
- Wood R. The New Whole Foods Encyclopedia. New
York, NY: Penguin Books; 1999.
- Robbins K, Gong Y,
Wells M, et al. Investigation of the antioxidant capacity and phenolic
constituents of US pecans. Journal of Functional
Foods. 2015;15:11-22.
- de la Rosa L,
Vazquez-Flores A, Pedraza-Chaverri J, et al. Content of major classes of
polyphenolic compounds, antioxidant, antiproliferative, and cell protective
activity of pecan crude extracts and their fractions. Journal of Functional Foods. 2014;7:219-228.
- Prado A, Aragao A,
Fett R, et al. Phenolic compounds and antioxidant activity of pecan (Carya illinoinensis (Wangenh.) K. Koch)
kernel cake extracts. Grasas Y Aceites
(España). 2009;(5):458.
- Haddad E, Jambazian
P, Karunia M, et al. A pecan-enriched diet increases γ-tocopherol/cholesterol
and decreases thiobarbituric acid reactive substances in plasma of adults. Nutrition Research. 2006;26:397-402.
- Müller L, Pase C,
Burger M, et al. Hepatoprotective effects of pecan nut shells on
ethanol-induced liver damage. Experimental
and Toxicologic Pathology: Official Journal of the Gesellschaft Für Toxikologische
Pathologie.
2013;65(1-2):165-171.
- Christen S, Woodall
AA, Shigenaga MK, et al. γ-tocopherol traps mutagenic electrophiles such as NOx
and complements α-tocopherol: Physiological implications. Proceedings of the National Academy of Sciences of the United
States of America.1997;94:3217–3222.
- Alasalvar C,
Bolling BW. Review of nut phytochemicals, fat-soluble bioactives, antioxidant
components and health effects. British
Journal of Nutrition. 2015;113 Suppl 2:S68-S78.
- Bouali I, Trabelsi
H, Berdeaux O, et al. Analysis of pecan nut (Carya illinoinensis) unsaponifiable fraction. Effect of ripening
stage on phytosterols and phytostanols composition. Food Chemistry. 2014;164:309-316.
- Pecan. Texas Texas
Beyond History website. Available at: www.texasbeyondhistory.net/st-plains/nature/images/pecan.html.
Accessed October 16, 2017.
- Moerman D. Native American Ethnobotany. Portland,
OR: Timber Press; 1998.
- Texas State
Symbols. Texas State Library and Archives Commission website. August 30, 2017.
Available at: www.tsl.texas.gov/ref/abouttx/symbols.html.
Accessed November 9, 2017.
- O’Neil C, Keast D,
Fulgon V, Nicklas T. Tree nut consumption improves nutrient intake and diet
quality in US adults: an analysis of National Health and Nutrition Examination
Survey (NHANES) 1999-2004. Asia Pacific
Journal of Clinical Nutrition. 2010;19(2):142-150.
- Kelly J, Sabaté J.
Nuts and coronary heart disease: an epidemiological perspective. British Journal of Nutrition. 2006;96
Suppl 2:S61-S67.
- Del Gobbo L, Falk
M, Feldman R, et al. Effects of tree nuts on blood lipids, apolipoproteins, and
blood pressure: systematic review, meta-analysis, and dose-response of 61
controlled intervention trials. American
Journal of Clinical Nutrition. 2015;102(6):1347-1356.
- Rajaram S, Burke K,
Connell B, et al. A monounsaturated fatty acid-rich pecan-enriched diet favorably
alters the serum lipid profile of healthy men and women. Journal of Nutrition. 2001;131(9):2275-2279.
- Hudthagosol C,
Haddad E, McCarthy K, et al. Pecans acutely increase plasma postprandial
antioxidant capacity and catechins and decrease LDL oxidation in humans. Journal of Nutrition. 2011;141(1):56-62.
- Lovejoy J. The
impact of nuts on diabetes and diabetes risk. Current Diabetes Reports. 2005;5(5):379-384.
- Morgan W,
Clayshulte B. Pecans lower low density lipoprotein cholesterol in people with
normal lipid levels. Journal of the
American Dietetic Association. 2000;100:312-318.
- Basic Report:
12142, Nuts, pecans. National Nutrient Database for Standard Reference Release
28. United States Department of Agriculture Agricultural Research Service.
Available at: https://ndb.nal.usda.gov/ndb/foods/show/3681.
Accessed October 16, 2017.
- Pecan pie energy
bites – vegan + gluten free. Gluten Free Vegan Pantry website. April 24, 2015.
Available at: www.glutenfreeveganpantry.com/pecan-pie-energy-bites-vegan-gluten-free/.
Accessed October 19, 2017.
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