Food as Medicine: Buckwheat

HerbalEGram: Volume 15, Issue 10, October 2018 (Fagopyrum esculentum; F. tataricum, Polygonaceae) By Jenny Pereza and Hannah Baumanb a ABC Education Coordinator b HerbalGram Associate Editor 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. We would like to acknowledge ABC Chief Science Officer Stefan Gafner, PhD, for his contributions to this project. Overview Buckwheat (Fagopyrum esculentum and F. tataricum) belongs to the Polygonaceae, or knotweed, family, a plant family with 40 known genera and approximately 1,200 species, which includes other edible plants such as common sorrel (Rumex acetosa) and rhubarb (Rheum rhabarbarum).1,2 Plants in this family have polygonum, or “many knees,” referring to the swollen nodes of the leaf stems.1 Commercially, buckwheat is grown for its fruits, leaves, and flowers that are obtained from either Fagopyrum esculentum, often referred to as common or sweet buckwheat, or F. tataricum, known as Tartary or bitter buckwheat.2-6 Both species are annual herbaceous plants that grow erect from a single hollow stem, which is succulent and smooth except at its characteristic swollen nodes.4 The plant grows rapidly to an average height of 1-3 feet and has soft, heart-shaped leaves and clustered groups of five small white to dark pink petal-like sepals.4,7 Its small dry fruits, botanically known as achenes, are grey to black and have a distinct triangular shape, a hard shell, and a starchy endosperm inside.7 These achenes are known commercially as “groats.” Despite its common name, buckwheat does not belong to the cereal grain family (Poaceae) but is considered a pseudocereal due to its similarities to wheat (Triticum aestivum, Poaceae) in terms of chemical characteristics and dietary uses.3 However, buckwheat does not contain gluten. The name buckwheat comes from the Dutch boekweit (boeke: “beech” and weite: “wheat”), which describes the resemblance of buckwheat seeds to beech (Fagus spp., Fagaceae) nuts as well as the wheat-like nature of buckwheat flour.7,8 Phytochemicals and Constituents Buckwheat groats and flour are considered important nutritional foods because of their high levels of protein, polyphenols, and minerals.5 Starch is the major nutritional component of buckwheat seed. The groats are high in B vitamins, including thiamin (B1), riboflavin (B2), and pyridoxine (B6), and they provide an array of minerals such as potassium, calcium, magnesium, zinc, copper, manganese, and selenium.3 In fact, buckwheat is considered a very good source of dietary magnesium, which is required for healthy nerves and muscles, and contains considerably more calcium than most cereal grains.8,9 Buckwheat’s fatty acid profile and total dietary fiber content is also considered superior to cereal grains.3 However, the high fiber content (17.8%) of buckwheat impedes the digestibility of its proteins.4 The protein content in buckwheat groats is well-balanced and extremely high compared to true cereal grains, and it has a biological value above 90%.3,6 (Biological value is a measure of how much protein is absorbed and integrated into the human body.) Buckwheat contains all nine essential amino acids and is particularly high in lysine, an amino acid found in limited quantities in cereal grains.3,4,8 Buckwheat also contains high amounts of arginine, tryptophan, and thiamine-binding proteins (TBPs), which act to stabilize and enhance the biological activity of thiamine.3 Foods that contain TBPs can be used to prevent dietary thiamine deficiencies.2,3 Despite the high protein content of buckwheat groats, the presence of trypsin inhibitors, fiber, and tannins lowers enzymatic availability, which can impede digestion and absorption of protein.3 The high antioxidant capacity and flavonoid content of buckwheat groats qualify buckwheat and buckwheat-enriched products as functional foods.3 Buckwheat groats are rich in antioxidant compounds, including glutathione, and have a very high polyphenol content, including catechins and flavonoids (e.g., rutin and quercetin).2,3 Rutin and quercetin are biosynthesized by plants in order to protect themselves from UV radiation, diseases, and predators.10 Buckwheat is among a few other field-grown crops that contain rutin, which is considered to be an important component of a heart-healthy diet.3,4 The leaves of buckwheat contain the highest amount of rutin in the plant.10 Tartary buckwheat contains more rutin than common buckwheat.2 Rutin has significant antioxidant and anti-inflammatory effects, and may also have antidiabetic and anti-hypertensive effects.2-4 Consuming 100 g (3.5 oz) of buckwheat flour or grains delivers roughly 10% of the daily therapeutic dose of rutin, which is considered to be between 180 and 350 mg.5 Buckwheat’s rutin levels decrease when exposed to heat; however, quercetin levels remain stable when heated. Although heat-treatment results in lower rutin levels in buckwheat breads and noodles, they are still considered nutrient-dense compared to raw flour.5 Historical and Commercial Uses Buckwheat, grown mainly for its groats, has been cultivated in China for at least 1,000 years.4,5 Buckwheat initially spread to Asia, reaching Japan 3,000 years ago from northern China via the Korean Peninsula.4 Buckwheat cultivation then spread to the Middle East and subsequently to Europe and Russia during the Middle Ages.7 From Europe, buckwheat arrived in North America in the 1600s, and early immigrants cultivated buckwheat on cleared lands to smother weeds and build soil.4,8 Today, Russia and China are the biggest producers of buckwheat globally.2,6 In traditional Chinese medicine (TCM), the leaf of the Tartary buckwheat is used to treat choking, ulcers, and hypertension, and to cleanse wounds. The flavonoid-rich leaves are also considered a nutritious food used to improve vision and hearing.4 Buckwheat is considered blood-building and detoxifying as it neutralizes acidic metabolic waste, and it is a staple of macrobiotic diets.9 In Nepal, Tartary buckwheat leaves are consumed to alleviate stomach disorders.4 Buckwheat groats are prepared raw or roasted, whole or powdered.11 To process buckwheat, the hulls enclosing the seeds are removed, and the seeds are typically roasted.3,11 Raw, hulled buckwheat seeds have a subtle flavor, while roasted, hulled buckwheat has an earthy, nutty flavor.8,11 Roasted, cooked groats have the consistency of porridge and are the basis of kasha, a traditional Russian dish cooked and served much like rice.7,11 In medieval Russia, the word kasha meant “meal” or “feast,” which referred to the belief that no meal was complete without buckwheat.9 Buckwheat flour is made from unroasted groats and typically includes a mixture of both hulled and unhulled buckwheat seeds. Depending on the amount hulled and unhulled seeds, buckwheat flour is graded light, medium, or dark.9 Unhulled buckwheat seed flour is the darkest in color and most nutritious, while flour made from hulled ground groats is the lightest in color and contains fewer nutrients.8,9 Buckwheat flour is used by a variety of diverse cultures, alone or as an ingredient in pancakes, French crepes, Southeast Asian unleavened breads (chapattis) and fried snacks (pakora), as well as Japanese soba noodles.4,7 To prevent rancidity, buckwheat seeds are stored with hulls and de-hulled shortly before use.4 A balanced amino acid profile can be achieved by mixing buckwheat with cereal grains, which are typically low in lysine.4 In Europe, buckwheat bread is gaining popularity as a nutrient-dense, antioxidant rich, gluten-free alternative to common cereal grains.5 Food science studies indicate that making wheat bread with 15% buckwheat flour functionally enhances its nutrient content and natural antioxidant capacity without compromising texture or flavor.3 In Europe and North America, buckwheat flour is typically blended with wheat flour to prepare pancakes, biscuits, noodles, and cereals.3 Aromatic buckwheat flowers provide both pollen and nectar for honeybees.3,8,11 Because honey production comes late in the season when other nectar sources are scarce, buckwheat is an important warm-weather, late-season crop for honeybees.4,11 Buckwheat honey has dark color, a distinct spiced flavor, and confirmed health benefits (see “Buckwheat Honey” section below).3 Modern Research A Gluten-free ‘Grain’ Unlike wheat, barley (Hordeum vulgare, Poaceae), and rye (Secale cereale, Poaceae), buckwheat grains lack α-gliadin and are low in prolamins (seed storage proteins that act as food antigens).3 These factors make buckwheat a healthy alternative for individuals with Celiac disease or non-Celiac gluten sensitivity (NCGS). Celiac disease is an autoimmune disease with both genetic and environmental components.3 Chronic intestinal inflammation can lead to malabsorption of several important nutrients, including iron and folate, which can lead to anemia and other ill effects.3 Strict adherence to a gluten-free diet is crucial to effectively treating Celiac disease and other gluten-sensitive individuals.3 A randomized, crossover trial with two intervention phases was conducted on 19 patients with NCGS over a period of 12 weeks.12 Participants either consumed a diet that consisted of buckwheat products or maintained their normal gluten-free diet without buckwheat supplementation. During the intervention period, those consuming buckwheat products experienced not only a significant reduction in the severity of abdominal pain and bloating, but also a significant increase in blood levels of magnesium and a reduction in pro-inflammatory cytokines.12 Type 2 Diabetes Dietary approaches are highly recommended for managing chronic diseases like type 2 diabetes mellitus (T2DM) and its associated cardiovascular, renal, and ocular complications.13 In many places where buckwheat is cultivated, it is traditionally used as both a food and a medicine. For example, in Taiwan and China, Tartary buckwheat is consumed daily to treat T2DM.5 Regular consumption of buckwheat products is strongly correlated with lower incidence of hyperglycemia and improved glucose tolerance.6 Buckwheat contains D-chiro-inositol (DCI), which is a primary mediator of insulin metabolism and has the ability to enhance glucose utilization and decrease blood pressure, plasma triglycerides, and glucose concentrations.6 Replacing or partially substituting buckwheat flour for white rice or wheat flour is a practical approach to disease management for patients with T2DM and those with a high risk of developing T2DM.13 Among all of the grains, buckwheat has the longest gastrointestinal transit time, which is associated with stabilized blood sugar levels and feelings of satiety.9 In a four-week clinical trial, 165 participants with T2DM who consumed Tartary buckwheat (> 110 g/d) experienced a 2.85% reduction in insulin, a 6.3% reduction in total cholesterol levels, and a 7.0% decrease in low-density lipoprotein (LDL) levels compared with the control group.13 Additionally, those who consumed buckwheat as part of their staple diet had a 15% increase in daily protein intake and a 25% increase in daily dietary fiber intake compared to baseline.13 A small clinical study of analyzed the effects on glucose and insulin on 10 healthy volunteers who consumed a single dose of boiled buckwheat groats, bread enriched with 50% buckwheat flour, or white wheat bread on separate days. Data showed that postprandial blood glucose and insulin production were lower when the subjects consumed buckwheat, especially buckwheat groats, than when the subjects consumed white wheat bread.2 Cardiovascular Health The bioflavanoids in green buckwheat tea may play a role in improving circulatory health.9,10 Rutin, for example, has been shown to increase the elasticity of blood vessels and arteries, enhance peripheral circulation, lower the risk of atherosclerosis and hypertension, and reduce capillary fragility.2-4,10 Two other compounds in buckwheat — γ-aminobutyric acid (GABA) and 2”-hydroxynicotianamine (H2N) — have been shown to possess blood pressure-reducing activity in vitro and in animals, possibly by inhibiting the action of angiotensin converting enzyme (ACE)-inhibitors.2,6 The use of buckwheat leaf and flower tea was investigated for its effects on leg adema in a randomized, double-blind, placebo-controlled trial of 67 patients with chronic venous insufficiency. Individuals who consumed buckwheat tea reported significant improvements in edema symptoms and less discomfort.5 Other studies have reported a rise in serum quercetin levels after consuming buckwheat tea, which may contributing to its potential anti-inflammatory and antioxidant effects.10 Buckwheat has also been studied for its ability to reduce unhealthy cholesterol levels including LDL and very low density lipoproteins.6 Buckwheat’s high fiber content helps lower cholesterol by increasing fecal excretion of sterols and decreasing absorption of dietary cholesterol.6,13 In a 2011 randomized, double-blind, placebo-controlled crossover study, 62 healthy volunteers were divided into two groups that consumed four cookies daily for four weeks. The active group received cookies enriched with buckwheat flour, and the control group were given cookies contained no buckwheat flour. After two weeks, the groups switched cookie types.2 The participants in the active group experienced significant decreases in levels of total cholesterol and myeloperoxidase (MPO), an enzyme that contributes to oxidative stress and inflammation.2 Oral Health In many traditional cultures, the seeds, roots, and bark of polyphenol-rich herbs are powdered and used as natural antibacterial and anti-inflammatory toothpowders to maintain oral hygiene and gum health. A clinical study reported a 62% improvement in periodontitis and bleeding gums in patients who brushed their teeth twice daily with Tartary buckwheat flour toothpowders.4 The improvements in gum tissue integrity were attributed to buckwheat’s vitamin and mineral contents, as well as the protective anti-inflammatory effects of rutin and quercetin.4 Buckwheat Honey Buckwheat honey provides antioxidant and antibacterial protection similar to New Zealand’s Manuka honey and has been studied for its powerful internal and external healing properties.14 Despite its own therapeutic benefits, buckwheat honey is not widely consumed due to its dark amber color and its strongly spiced odor and malty flavor.14 The flavor, composition, and biological activities of honey vary upon type of botanical forage and geographical location. Research indicates that dark-colored honey contains higher levels of phenolic compounds and has, therefore, a more potent antibacterial and antioxidant capacity.14 Higher mineral content in honey is also associated with a darker color and stronger flavor. Buckwheat honey has a higher protein content than most honeys and delivers more iron, calcium, magnesium, manganese, and zinc.14 A 2007 clinical study of 105 children with acute nocturnal cough due to upper respiratory illness were randomly assigned to one of three groups: an active group given a single nocturnal dose of buckwheat honey, an active control group given single nocturnal dose of artificial honey-flavored dextromethorphan (an over-the-counter antitussive), or the control group which received no treatment.15 Results indicated that the group treated with buckwheat honey had significantly greater symptom relief (reduced cough severity, and frequency while improving child’s sleep quality) than participants in the other two groups.15 In vitro, both Manuka and buckwheat honey have been shown to inhibit Staphylococcus aureus, a bacteria that causes a wide range of common skin infections and life-threatening illnesses such as pneumonia and sepsis.14 Studies by Zhou et al. have demonstrated buckwheat honey’s ability to prevent hydroxyl radical-induced DNA damage through its inherent antioxidant components.2 Consumer Considerations Buckwheat’s nutritional, dietetic, and therapeutic properties make it an important global food crop to cultivate especially as access to arable land and water become more challenging.2 Compared to cereal grains, buckwheat requires fewer soil nutrients and less water, and has the additional benefits of naturally suppressing weeds, improving soil health, fostering beneficial insects, and providing forage for livestock and poultry.2,7,11 Due to its very high protein content, buckwheat complements cereal grains and helps provide a more complete protein when combined with typical cereal grains and flours.8 Consuming buckwheat or buckwheat-containing foods frequently and in high amounts can cause IgE antibody-mediated allergic reactions.2 Additionally, it is important to be aware that buckwheat sprouts, despite their growing popularity, contain napthodianthrones, more specifically the fagopyrins that can cause photosensitization or skin irritation after sunlight exposure.5 Buckwheat sprouts should not be consumed in excess by poultry, livestock, or humans.5 Consumers should be aware that gluten-free products tend to be deficient in B vitamins, calcium, iron, zinc, magnesium, and fiber while also containing higher amounts of added sugar or fat.12 The dietary use of pseudocereals, like buckwheat, could improve dietary intake of protein, iron, calcium, and fiber.12 Nutrient Profile16 Macronutrient Profile: (Per 100 grams buckwheat groats) 343 calories 13.3 g protein 71.5 g carbohydrate 3.4 g fat Secondary Metabolites: (Per 100 grams buckwheat groats) Excellent source of: Manganese: 1.3 mg (56.5% DV) Magnesium: 231 mg (55% DV) Dietary Fiber: 10 g (33% DV) Riboflavin: 0.43 mg (33% DV) Niacin: 7.02 mg (43.9% DV) Phosphorus: 347 mg (27.8% DV) Very good source of: Vitamin B6: 0.21 mg (12.4% DV) Iron: 2.2 mg (12.2% DV) Good source of: Potassium: 460 mg (9.8% DV) Thiamin: 0.101 mg (8.4% DV) Folate: 30 mcg (7.5% DV) Also provides: Calcium: 18 mg (1.4% DV) DV = Daily Value as established by the US Food and Drug Administration, based on a 2,000-calorie diet. Recipe: Kasha Cereal9 Ingredients: 1 cup buckwheat groats 4-5 cups boiling water 1/2 onion, diced (optional) Salt to taste Directions: Place all ingredients in a large pot and bring to a boil. Cover, reduce heat to low, and simmer for 30 minutes until soft. Photo credit: Buckwheat (Fagopyrum esculentum) All photos ©2018 Steven Foster References Elpel T. Botany in a Day: The Patterns Method of Plant Identification. Pony, MT: HOPS Press LLC; 2004. Gimenez-Bastida JA, Zielinski H. Buckwheat as a functional food and its effects on health. J Agr Food Chem. 2015;63:7896-7913. Wronkowska M, Soral-Smietana M, Krupa-Kozak U. Buckwheat, as a food component of a high nutritional value, used in the prophylaxis of gastrointestinal disease. Eur J Plant Sci Biotech. 2010;4(Special Issue 1):64-70. Campbell CG. Buckwheat (Fagopyrum esculentum). International Plant Genetic Resources Institute. 1997. Kade Research Ltd. Morden, Manitoba, Canada. Kreft M. Buckwheat phenolic metabolites in health and disease. Nutr Res Rev. 2016;29:30-39. Zhang ZL, Zhou ML, Tang Y, et al. Bioactive compounds in functional buckwheat food. Food Res Int. 2012;49:389-395. Van Wyk B. Food Plants of the World: An Illustrated Guide. Portland, OR: Timber Press; 2006. Murray M, Pizzorno J. The Encyclopedia of Healing Foods. New York, NY: Atria Books; 2005. Pitchford P. Healing with Whole Foods: Oriental Traditions and Modern Nutrition. Berkeley, CA: North Atlantic Books; 1993. Kreft I, Fabjan N, Germ M. Rutin in buckwheat – Protection of plants and its importance for the production of function food. Fagopyrum. 2003;20:7-11. Buckwheat. Encyclopedia Britannica website. Available at: www.britannica.com/plant/buckwheat. Accessed on October 2, 2018. Dinu M, Macchia D, Pagliai G, et al. Symptomatic efficacy of buckwheat products in Non-Celiac Gluten Sensitivity (NCGS). Asian Pac J Clin Nutr. 2017;26(4):630-636. Qiu J, Liu Y, Yue T, et al. Dietary Tartary buckwheat intake attenuates insulin resistance and improves lipid profiles in patients with type 2 diabetes: a randomized controlled trial. Nutr Res. 2016;36:1392-1401. Deng J, Liu R, Lu Q, et al. Biochemical properties, antibacterial and cellular antioxidant activities of buckwheat honey in comparison to Manuka honey. Food Chem. 2018;252:243-249. Paul IM. Therapeutic options for acute cough due to upper respiratory infections in children. Lung. 2012;190:41-44. Agricultural Research Service. National Nutrient Database for Standard Reference Legacy Release. United States Department of Agriculture website. April 2018. Available at: https://ndb.nal.usda.gov/ndb/foods/show/20008. Accessed October 5, 2018.