April 2017 Issue

Exceptional, Enjoyable Edamame
By Judith C. Thalheimer, RD, LDN
Today's Dietitian
Vol. 19, No. 4, P. 24

Once an exotic rarity, these tasty beans are now widely available, easy to cook, and a highly nutritious and well-accepted addition to any diet.

The popularity of edamame (ed-ah-MAH-may) is growing worldwide.1 These immature green soybeans in their tough, hairy pods are nutritional gems that are as tasty and fun to eat as they are healthful. Sometimes called green vegetable soybeans, edamame is the second most popular soyfood in America, after soymilk. "Edamame is actually the term used for immature soybeans in the pod," says Torey Armul, MS, RD, CSSD, LDN, a spokesperson for the Academy of Nutrition and Dietetics (the Academy). "The Japanese term for these beans out of the pod is mukimame, although in US markets you're likely to see them listed as 'shelled edamame.'"

Edamame became popular in America with the sushi boom in the 1980s. Early Japanese restaurants in California reportedly served them with Japanese beer as a culturally appropriate substitute for the peanuts often served at American bars. In 1994, packaged ready-to-eat edamame appeared in a supermarket for the first time.2

With their familiar lima bean shape, pealike pod, and pleasant taste and texture, edamame may be more appealing than a block of tofu or a chunk of tempeh. "Edamame is a great way to open people up to the whole world of soyfoods," says Mark Messina, PhD, a noted soy researcher and executive director of the Soy Nutrition Institute in St. Louis.

Powerful Nutrition Profile
Edamame is packed with nutrients that make it a standout even among other soyfoods. While nutrition analyses vary, 1 cup of cooked beans provides approximately one-third the DV of both protein and fiber, with just under 200 kcal.3 "Edamame has an outstanding nutrition profile," Armul says. "I can't think of many foods that low in calories and also that high in protein and fiber." As complete proteins, soybeans have all nine of the essential amino acids.4

The United Soybean Board’s 2014 report “Consumer Attitudes About Nutrition, Health and Soyfoods,” found that 75% of consumers perceive soy products as healthful.5 In 1999, the FDA approved a health claim linking soy protein intake to reduced risk of heart disease.6 This endorsement led to a general rise in demand for soyfoods, including an increase in the popularity of edamame.5 The SANA report indicates that sales of these tender beans have been growing steadily, up 9% from 2010 to 2013, the latest year for which data are available.5

A daily intake of 25 g soy protein (as part of a diet low in saturated fat and cholesterol) is recommended to potentially lower heart disease risk.6 One cup of prepared edamame (in the pod) provides around 18 g.7 One-half cup of boiled shelled edamame beans has 10 g protein.7

The protein in edamame isn't just complete; it's also well-balanced by other macronutrients. About one-third of the calories in edamame beans come from protein, one-third from carbohydrate, and one-third from fat.3 Vandana Sheth, RDN, CDE, a diabetes educator and spokesperson for the Academy, recommends edamame as a snack for her clients with diabetes. "It has the right balance of protein and carbohydrate, plus fiber to increase satiety," Sheth says. Moreover, soyfoods, including edamame, are a good source of both omega-6 (linoleic acid) and omega-3 (alpha-linolenic acid) polyunsaturated fats, with 1 cup of cooked beans providing nearly 3 g omega-6 and nearly 0.6 g omega-3 (as much as 1 oz of walnuts).3,8

In addition to an admirable macronutrient profile, edamame is packed with vitamins and minerals. It's an excellent source of thiamin, iron, magnesium, phosphorus, copper, vitamin K, folate, and manganese (see Table 1 for more information).7 It's also rich in phytochemicals and active compounds (see Table 2 on page 28).8 But the star of the nutrition show for these beans, as for all soyfoods, is isoflavones. "Isoflavones are what make soyfoods so interesting and valuable," Messina says. "There have been an enormous number of studies on soy isoflavones."

Soybeans and soy products are the richest source of isoflavones in the human diet.9 Isoflavones are phytoestrogens, plant chemicals that are capable of exerting estrogenlike effects.9 "The fact that isoflavones are classified as phytoestrogens has created some controversy around soyfoods," Messina says. Breast cancer, especially estrogen receptor-positive breast cancer, is a primary concern. Rats that were exposed to high doses of isoflavones in some animal studies showed an increased risk of breast cancer, but rats process soy differently from humans.10 "In the 1990s, animal research began to be published suggesting isoflavones might worsen the prognosis of breast cancer patients," Messina says, "but the human data that began to be published in the late 2000s suggest postdiagnosis soy intake could actually reduce recurrence and mortality."

According to Marji McCullough, ScD, RD, strategic director of nutritional epidemiology for the American Cancer Society, epidemiologic studies that followed large populations of healthy women for many years (particularly studies in Asian countries where lifelong soy consumption is higher than in the United States) have shown either no association between soy and breast cancer or a protective association from eating soyfoods like edamame.

McCullough offers some explanation as to why soy's phytoestrogens may not be the powerful cancer-causers they were once thought to be. "While isoflavones may act like estrogen, they also have antiestrogen properties," McCullough explains. "That is, they can block the more potent natural estrogens from binding to the estrogen receptor. In addition, they stop the formation of estrogens in fat tissue and stimulate production of a protein that binds estrogen in the blood, making it less able to bind to the receptor. They also have antioxidant and anti-inflammatory properties and may work in other ways to reduce cancer growth."

While old information associating soy with cancer persists in the public imagination, the American Cancer Society states that no reliable studies have pointed to any dangers from eating edamame and other soyfoods, and the health benefits appear to outweigh any potential risk.10 The American Institute for Cancer Research considers soy a food that fights cancer.8

While the immature beans have less isoflavones than mature soybeans, and about 50% to 60% is lost in processing (boiling, freezing, or freeze-drying), edamame still is a rich source of isoflavones.11,12 "Soy products are essentially the only meaningful source of isoflavones among commonly consumed foods," Messina says. "Because Americans eat so little soy, they get only a couple of milligrams of isoflavones per day on average. A serving of a traditional soy food provides about 25 mg." One-half cup boiled green soybeans has 16 mg total isoflavones, which is less than that found in a serving of tofu, tempeh, or aqueous washed soy protein concentrate, but more than soymilk, which has just over 6 mg per cup.9

Edamame stacks up well nutritionally against other soyfoods. "Tempeh is more calorie dense and higher in fat than a similar serving of edamame," Armul says, "and soymilk is lower in calories but has much less protein and fiber. Tofu, like edamame, is low in calories while still being a good source of protein, without all the saturated fat of animal proteins, but edamame has more fiber."

Whether or not edamame has a more favorable impact on health than other soyfoods is impossible to say. "There's little data on any unique health benefits edamame may have compared with other soyfoods, because edamame isn't used in clinical trials," Messina says. "In most trials, participants need to be blinded, and they all need to consume a precise amount of whatever is being studied each day, so clinical research on soy is typically conducted using isoflavone pills or soy protein powder provided in the form of a beverage or muffin."

Eating Edamame
Getting clients to add edamame to their diets may not be difficult. "In my experience, edamame is the soyfood people like the most in terms of taste," Messina says.

Armul agrees: "Edamame has a pleasant sweetness that makes it very appetizing," she says.

According to Keshun Liu, PhD, a research chemist at the USDA's Agricultural Research Service, it's scientific fact that immature soybeans taste better than mature beans. "This is a result of at least three aspects: higher simple sugars that make them sweeter than mature beans, higher free amino acids that give them a meaty taste, and their tender texture," Liu says.

They're also fun to eat. Once the pods are cooked, the beans can be popped directly into the mouth of the person eating them by pulling the pod through lightly closed teeth.

"Often, people don't realize there are so many ways to eat edamame," Sheth says. "Boiling, steaming, or microwaving the pods and then sprinkling them with salt is traditional. Using some of the interesting salts on the market, such as black or truffle salts, is a little different and unique, but salt isn't the only option. My favorite way to eat edamame is cooked in a wok with a little oil, garlic, and crushed chili peppers or chili paste. You get so much flavor on the pod, and you get that flavor as you pull the pod through your teeth to remove the beans."

Fresh edamame may be found in season in the refrigerated produce section of the supermarket. They should be crisp and free from blemishes. Frozen edamame, in the pod or shelled, are available where frozen vegetables are sold.13

To cook, boil the pods or beans for four to five minutes on the stovetop, or place the edamame in a dish, add water, and then microwave covered on high for two to three minutes.13 "It's hard to mess up cooking them," Armul says, "and they're delicious eaten hot, cold, or room temperature, as part of a dish, or alone." She adds edamame to a wide variety of dishes. "I love them thrown in a salad. It's a great way to add protein," Armul says. "They're very versatile and pick up a lot of different flavors. But edamame is also just a great snack on its own. I buy the frozen precooked beans. Just thaw them in the fridge or on the counter and enjoy."

Sheth adds shelled edamame to pilafs, casseroles, pastas, soups, or stews. "They add a nice addition of flavor and nutrients in grains such as rice, couscous, or quinoa," Sheth says. "I also like adding the beans to salads or puréeing them to make a dip or a spread for a wrap or sandwich. Add puréed edamame beans to mashed avocado for a guacamole with added protein and fiber."

Edamame also makes a great snack for kids. "Since many of the proposed benefits of soy relate to its ability to reduce chronic disease risk over the long term, I'd recommend them as a great food for kids," Messina says. "There's a possibility that consuming soy early in life reduces breast cancer risk. In fact, epidemiologic studies suggest that one serving of soyfoods per day for children and teens could potentially reduce breast cancer risk 25% to 50%."

Easy to cook, fun to eat, versatile, and delicious, edamame is one healthful food consumers will be ready and able to eat on a regular basis. "I believe that edamame is an underused, underestimated food," Armul says, "whether for vegetarians, vegans, or anyone looking to add more plant-based proteins to their diet."

— Judith C. Thalheimer, RD, LDN, is a freelance nutrition writer, speaker, and community educator in Philadelphia.

References
1. Williams MM. Managing weeds in commercial edamame production: current options and implications. Weed Sci. 2015;63(4):954-961.

2. Shurtleff W, Aoyagi A; Soy Info Center. History of edamame, green vegetable soybeans, and vegetable-type soybeans (1275–2009). http://www.soyinfocenter.com/pdf/133/GVS.pdf. Published 2009.

3. Edamame, frozen, prepared: nutrition facts & calories. SELF Nutrition Data website. http://nutritiondata.self.com/facts/vegetables-and-vegetable-products/9873/2#ixzz4WbOHdkqF

4. Rivette C. Edamame is hard to say but easy (and nutritious) to eat. Michigan State University Extension website. http://msue.anr.msu.edu/news/edamame_is_hard_to_say_but_easy_and_nutritious_to_eat. Published March 27, 2012.

5. Soy products: sales and trends. Soyfoods Association of North America website. http://www.soyfoods.org/soy-products/sales-and-trends. Published 2014.

6. Food and Drug Administration. CFR Code of Federal Regulations, Title 21. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=101.82. Updated September 21, 2016.

7. United States Department of Agriculture, Agricultural Research Service. USDA Food Composition Databases. https://ndb.nal.usda.gov/ndb/search/list

8. AICR's foods that fight cancer: soy. American Institute for Cancer Research website. http://www.aicr.org/foods-that-fight-cancer/soy.html

9. Higdon J, Drake VJ, Delage B, Duncan AM. Soy isoflavones. Oregon State University Linus Pauling Institute website. http://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/soy-isoflavones#food-sources. Updated October 2016. Accessed February 2017.

10. Simon S. How your diet may affect your risk of breast cancer. American Cancer Society website. http://www.cancer.org/latest-news/how-your-diet-may-affect-your-risk-of-breast-cancer.html. Published May 21, 2015.

11. Wu Q, Wang M, Sciarappa WJ, Simon JE. LC/UV/EIS-MS analysis of isoflavones in edamame and tofu soybeans. J Agric Food Chem. 2004;52(10):2763-2769.

12. Simonne AH, Smith M, Weaver DB, Vail T, Barnes S, Wei CI. Retention and changes of soy isoflavones and carotenoids in immature soybean seeds (edamame) during processing. J Agric Food Chem. 2000;48(12):6061-6069.

13. Green soybeans (edamame): nutrition, selection, storage. Fruits and Veggies More Matters website. http://www.fruitsandveggiesmorematters.org/green-soybeans-edamame-nutrition-selection-storage