Food as Medicine: Pecan (Carya illinoinensis, Juglandaceae)
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.4In 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.2,8Eighty 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.4They 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 (Macadamiaspp., 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 bloodstream. 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 pacanesor 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.4This 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
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.
Nut consumption has been linked to lowered risk of cardiovascular events such as heart attacks.4,23Epidemiological 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
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
Macronutrient Profile: (Per 1 ounce [approx. 28.4 grams])
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)
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)
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.