Food as Medicine: Rutabaga (Brassica napus subsp. rapifera, Brassicaceae)

HerbalEGram: Volume 13, Issue 8, August 2016

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 thank Melanie Leslie (TSU, 2015) for her research and work on rutabaga. Overview Rutabaga (Brassica napus subsp. rapifera, Brassicaceae), also known as “swede” or “Swedish turnip,” is a natural hybrid between cabbage (B. oleracea) and turnip (B. rapa).1 It can also be found under the subspecies “napobrassica.” Considered a root vegetable, the rutabaga is actually the enlarged base of the stem of the plant.2 Most commonly, rutabagas have a pale yellow or white inner flesh and a darker yellow or purple exterior. Rutabaga is a relative newcomer to the world of domesticated crops, with its first mention in botanical literature appearing in the 17th century.3 The nickname “swede” comes from the plant’s geographical origin, as it became a fixture in Swedish agriculture before spreading around the world.4 It was introduced in North America in the early 19th century. A biennial plant that stores well, rutabaga thrives in cooler climates where the summer season is not excessively hot.5 Rutabagas are considered a root crop, and lend themselves to longer post-harvest storage when placed in a root cellar or similar environment that is damp and cool, lasting up to six months in storage.6,7 To prevent loss of moisture during storage or transit, the green tops are removed and the bulbs are waxed.5 Phytochemicals and Constituents Rutabagas are rich in carbohydrates and fiber and contain little fat or protein.8 They contain about half of the calorie content of potatoes, and are relatively high in vitamin C and potassium. A diet high in fiber has many benefits, primarily for the gastrointestinal tract.9 Insoluble fiber, which cannot be absorbed and digested, promotes healthy bowel movements and lowers the risk of developing disorders such as acid reflux, ulcers, constipation, hemorrhoids, and diverticulosis, a condition in which small, bulging pouches develop along the digestive tract. These pouches can become inflamed, which is known as diverticulitis, causing abdominal pain and fever and requiring treatment. The fiber content of rutabagas consists mostly of insoluble fiber, which, in addition to maintaining bowel health, may also lower the risk of cardiovascular disease, hypertension, diabetes, stroke, and obesity.10 Potassium is an essential mineral for the body. It functions as an electrolyte, conducting electricity through the body, ensuring the proper function of cells, tissues, and organs.11 Other important electrolytes include sodium, chloride, calcium, and magnesium. Maintaining healthy potassium levels is vital for maintaining bone health, especially for the aging population, and people with diets high in potassium are at lower risk for stroke and heart disease. Additionally, potassium levels depend on an inverse relationship with salt intake: those who consume too much sodium in proportion to potassium will have less potassium available for absorption by the body.12 Other bioactive components in rutabagas include glucosinolates and phenols, similar to other plants in the Brassicaceae family, such as broccoli (Brassica oleracea)13. Glucosinolates are precursors to isothiocyanates, which may reduce the risk of certain cancers.14 In the plant, glucosinolates are converted to isothiocyanates by an enzyme called myrosinase. However, the enzyme is deactivated with excessive heat, so cooking rutabaga will impact the conversion of glucosinolates to isothiocyanates. Gut bacteria also have this ability to convert glucosinolates to isothiocyanates. Phenols act as antioxidants, which reduce free radicals in the body. Historical and Commercial Uses The cultivation of rutabagas began in the 1600s in Bohemia (which now makes up the western Czech Republic) before they made their way to Scandinavia, where the cold-weather crop was embraced as both food for humans and livestock.6 By the 18th century, rutabaga consumption had spread to France and England.2 Rutabagas were introduced in the United States in the early 19th century, where they were primarily grown as livestock fodder. Because the plant is so hardy and grows well in bad weather conditions, rutabagas became associated with times of scarcity, which impacted their popularity as a food product. Even in modern times in the United States, they are not as widely consumed as other, more familiar root vegetables. However, the rutabaga has had some interesting cultural impacts.  Jack o’ lanterns are a Halloween tradition with roots in Irish culture. The origin myth tells the story of a trickster named Jack, who thwarted the devil’s plan to take his soul and found his way out of hell with the aid of a burning ember and a hollowed-out rutabaga (or “turnip”).15 Though the rutabaga’s colloquial name of “turnip” in the British Isles has resulted in the erroneous belief that Brassica rapa was used, it is accepted by the standard lore that rutabagas were, in fact, the first jack o’ lanterns. When the practice migrated to the United States, where pumpkins (Cucurbita pepo, Cucurbitaceae) were readily available and already involved in many fall celebrations, the pumpkin replaced the rutabaga.  Many towns with a prominent Scandinavian population have events to celebrate the rutabaga and its place in cultural traditions. One of the more tongue-in-cheek celebrations is the International Rutabaga Curl competition, which has been a tradition in Ithaca, New York, since 1996.16 Notably, in 2016, the town of Cumberland, Wisconsin, held its 84th Annual Rutabaga Festival Parade.  Modern Research In a recent study, rutabaga methanol extracts killed human liver cancer cells in vitro and also decreased the rate of cancer cell proliferation.17 The normal, non-cancerous cells were not affected. Compared to root or seed extracts, rutabaga sprout extracts were more effective at battling liver cancer cells. This was due to the significantly higher levels of flavonoids found in the rutabaga sprout, which correlated to stronger antioxidant activity. Rutabaga is a variety of the rapeseed plant (Brassica napus, Brassicaceae). Brassica napus contains plant sterols that, in isolation, have shown effects against prostate cancer cells.18 The sterol called brassinolide induced apoptosis (normal, pre-programmed cell death) in these prostate cancer cells during in vitro trials. Researchers concluded that brassinolide “might therefore be a promising candidate for the treatment of prostate cancer.” The bioactive compounds present in cruciferous vegetables, including rutabagas, have been studied for many different conditions. A randomized, crossover, controlled study showed that intestinal bacteria were changed within two weeks of eating a diet rich in cruciferous vegetables, although the bacterial colonization was different with each study participant.19 A hospital-based, case-control study showed that consumption of raw, rather than cooked, cruciferous vegetables decreased risk of bladder cancer.20Additionally, growth conditions can impact the glucosinolate content in cruciferous vegetables.21Supplementing the soil with selenium, nitrogen, or sulfur was correlated with an increase in glucosinolate content, but when applied in excess had an inhibiting effect. Rutabaga’s status as a nutritious food has often been overlooked in the United States. Combined with its ease of preparation and possible health benefits, this less-glamorous cousin of cabbage and turnips deserves a popularity renaissance. Nutrient Profile8 Macronutrient Profile: (Per 1 cup raw rutabaga cubes [approx. 140 g]) 52 calories 1.5 g protein 12.07 g carbohydrate 0.22 g fat Secondary Metabolites: (Per 1 cup raw rutabaga cubes [approx. 140 g]) Excellent source of: Vitamin C: 35 mg (58.3% DV) Very good source of: Potassium: 427 mg (12.2% DV) Dietary Fiber: 3.2 g (12.8% DV) Good source of: Manganese: 0.18 mg (9.2% DV) Thiamin: 0.13 mg (8.7% DV) Phosphorus: 74 mg (7.4% DV) Folate: 29 mcg (7.3%DV) Magnesium: 28 mg (7.0% DV) Vitamin B6: 0.14 mg (7.0% DV) Calcium: 60 mg (6.0% DV) Also provides: Niacin: 0.98 mg (4.9% DV) Riboflavin: 0.06 mg (3.5% DV) Iron: 0.62 mg (3.4% DV) Vitamin E: 0.42 mg (1.4% DV) DV = Daily Value as established by the US Food and Drug Administration, based on a 2,000-calorie diet. Recipe: Honey-Lemon Glazed Rutabagas and Carrots Adapted from: Bon Appétit22 Ingredients: 1 1/4 pounds rutabaga, peeled and sliced into matchstick-sized strips 1 pound carrots, peeled and sliced into matchstick-sized strips 1/4 cup unsalted butter 1/4 cup freshly-squeezed lemon juice 1 teaspoon grated lemon zest 3 tablespoons honey 1/2 cup fresh chives, minced Salt and pepper to taste Directions: In a large saucepan, bring lightly salted water to boil. Add rutabagas and cook for 2 minutes. Add carrots and cook until vegetables are tender, about 3 minutes. Drain. Melt butter in a large saucepan over medium-high heat. Add lemon juice, zest, and honey. Bring to a boil. Add the vegetables and cook until glazed, stirring occasionally, about 6 minutes. Season to taste with salt and pepper. Remove from heat and stir in chives. —Hannah Bauman References Van Wyk BE. Food Plants of the World. Portland, OR: Timber Press; 2006. Davidson A. The Oxford Companion to Food. 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