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By Malia Frey, M.A., ACE-CHC, CPT
Updated on January 03, 2021
Medically reviewed by Ayana Habtemariam, MSW, RDN, LDN
Natto is fermented soybeans. Often consumed as a breakfast food, the brown, sticky, concoction has a distinctive smell that can be compared to a pungent cheese. The powerful flavor is often described as earthy or nutty and somewhat bitter. While the food is most commonly consumed in Japan, it is slowly making its way into markets in the U.S. and other western countries due to its health benefits.
Natto is considered a superfood for several reasons, including its potential effects on the digestive system. Soybeans provide well-documented nutritional benefits. Studies are ongoing about the impact that natto has on overall health and wellbeing.
Nutrition Facts
The following nutrition information is provided by the USDA for one cup (175 grams) of natto.1
Calories: 369
Fat: 19.2g
Sodium: 12.2mg
Carbohydrates: 22.2g
Fiber: 9.5g
Sugars: 8.6g
Protein: 34g
Carbs
There are different types of carbohydrates in natto. Each type provides different benefits.
You'll get about 6 grams of naturally-occurring sugar if you consume one cup of natto. Sugar that occurs naturally in foods is less of a concern than sugars that are added to food as part of processing (called "added sugars"). Sugar provides the body with energy for daily activities.
Another form of carbohydrates in natto is fiber. You'll get over nine grams when you consume a full cup of the fermented food. The USDA recommends that adults consume 28 grams of fiber per day. Consuming fiber not only improves digestion and regularity, but it also provides many other health benefits, including decreased risk of some types of cancer, obesity, cardiovascular disease, and diabetes.2
The remaining carbohydrate in natto is starch, which is broken down to provide fuel for your brain and muscles.
The glycemic load (GI) of natto is estimated to be nine when one cup is consumed. Glycemic load takes portion size into account when estimating a food's impact on blood sugar. However, natto is often consumed with rice—a higher glycemic food. The University of Sydney estimates the glycemic load of a 150-gram serving of white rice and natto to be 24. Foods with a glycemic load of 20 or higher are considered to be high glycemic foods.3
Fats
Natto provides just over 19 grams of fat in a one-cup serving. Most of that fat is polyunsaturated. Polyunsaturated fats help reduce low-density lipoprotein (LDL) cholesterol and can help lower your risk of heart disease and stroke. Natto also provides about four grams of monounsaturated fat—also considered a "good" fat. And there are just under three grams of saturated fat in natto.
Dietary Fat Structure, Digestion, and Function
Protein
Natto is a high-protein food. You'll boost your intake of plant-based protein by 34 grams when you consume a full cup.
Vitamins and Minerals
Natto is packed with micronutrients. A serving of natto provides 2.7mg of manganese, a whopping 134% of your daily recommended intake. Manganese is important for enzyme function in the body and other functions including blood clotting and metabolism.4
You'll also get about 15 grams of iron (84% of your daily needs), 1.2 mg of copper (58% of your daily needs), 201 mg of magnesium (50%), 1,276 mg of potassium (36%), 5.3 mg of zinc (35%), 305 mg of phosphorus (30%), and 15.4 mcg of selenium (22%).
You'll also benefit from the vitamins that natto supplies. The food is high in vitamin C, providing almost 23 mg or about 38% of your daily needs. Vitamin C helps to boost your body's immune system, build collagen, and improve the absorption of iron from plant-based foods. It is also an antioxidant that can help your body repair the damage from free radicals.5
Natto contains 0.3 mg of thiamin (19% of your daily needs), 0.3 mg of riboflavin (20%), vitamin B6, folate, and choline.
Lastly, natto is often cited as one of the best sources of vitamin K, particularly vitamin K2. Your body uses vitamin K to form bone and prevent blood clotting. The National Institutes of Health recommends that adult women get at least 90 mcg of the vitamin per day and men get at least 120 of vitamin K per day.6 A one-cup serving supplies over 40 micrograms of vitamin K.
Health Benefits
Natto has been studied for a wide range of benefits that the food may provide. These are some of the most significant findings.
Provides Gastrointestinal Benefits
Natto is fermented with a specific type of bacteria called Bacillus subtilis. Researchers are studying the potential of this and other Bacillus strains to improve gut health in humans. They do know that this bacteria provides probiotic benefits.7
Probiotics are living, healthy microorganisms found in the gastrointestinal system and help protect the gut from unhealthy microorganisms, improve digestion, and may provide other health benefits.8 The extent of their impact is still being explored.
There is some limited evidence that consuming natto and other fermented foods may positively influence stool frequency, especially in those managing constipation.9 More trials need to be conducted to further understand the benefit.
Other Probiotic Foods to Boost Gut Health
Might Improve Bone Density
Vitamin K2, found in natto, is showing promise in the management of several conditions including diabetes, cancer, and particularly osteoarthritis.10
One study published in Osteoporosis International examined the impact of natto intake on the bone health of elderly Japanese men. After studying over 1,600 men, researchers found that those who consumed more natto experienced increased bone health as a result of the vitamin K content. However, researchers noted that more studies are needed to understand the association.11
Another study examined natto consumption in older women. For the study, 944 postmenopausal Japanese women were studied over the course of three years.
Women who habitually consumed more natto showed greater bone mineral density at several locations in the body, including the hip and neck. However, other sites throughout the body showed no change.
Interestingly, the researchers did not see this benefit with increased intake of tofu or other soybean products.12
Tofu Nutrition Facts and Health Benefits
Improves Cardiovascular Health
Nattokinase is an enzyme produced in natto during the fermentation process. It acts as a natural blood thinner and assists in the prevention of arterial plaque formation.
Researchers have found that nattokinase may provide cardiovascular benefits including a reduction in the risk of cardiovascular disease. More specifically the enzyme has demonstrated antihypertensive, anti-atherosclerotic, and lipid-lowering, anti-platelet, and neuroprotective effects, according to several research studies.13
May Improve Longevity
Because nattokinase has been linked to substantial reduction in the risk for cardiovascular disease, researchers have also linked it to improved longevity. Cardiovascular disease is the leading cause of death in the world.
According to the authors of a 2018 study, "natto consumption is believed to be a significant contributor to the longevity of the Japanese population. Recent studies demonstrated that a high natto intake was associated with decreased risk of total cardiovascular disease mortality and, in particular, a decreased risk of mortality from ischaemic heart diseases.13
May Lower Blood Pressure
Many studies involving natto are conducted on people living in Japan, where the food is more commonly consumed. But one study involved 79 participants with elevated blood pressure, all living in North America. Researchers found that consumption of nattokinase was associated with a reduction in both systolic and diastolic blood pressure in both men and women. The data collected from women suggested a possible reduction of risk for stroke.14
Allergies
The Centers of Disease Control and Prevention has identified eight major food allergies in the United States. Soy is one of them. The others are milk, egg, peanut, tree nuts, wheat, fish, and crustacean shellfish.15 Those with a soy allergy should avoid natto.
Recipes
The Cleveland Clinic also identifies symptoms in adults including itching, hives, eczema, swelling of the lips, tongue, or throat, chest tightness or difficulty breathing, wheezing, dizziness, fainting and in severe cases, anaphylaxis.16 Children with soy allergies may experience chronic vomiting, diarrhea, and failure to gain weight or height, according to the National Institute of Allergy and Infectious Disease.17
Adverse Events
Soy may interact with certain medications. Memorial Sloan Kettering Cancer Center identifies several medications and classes of medication that may interact with soy.18 They include:
Aromatase inhibitors
Cytochrome P450 substrate drugs
P-Glycoprotein substrate drugs
Tamoxifen
Uridine 5’-diphospho-glucuronosyltransferase (UGT) substrate drugs
If you are not sure if your medication falls into one of these categories, speak to your healthcare provider to get personalized advice.
There has also been some concern about the impact of soy on women's health. Specifically, some are concerned that soy consumption may increase the risk of endometrial hyperplasia. However, the National Institutes of Health advises that soy foods do not appear to increase the risk of the condition. Furthermore, the agency states that it is safe for women who have had breast cancer or who are at risk for breast cancer to eat soy foods.19
Lastly, some people are concerned about antinutrients in soybeans. Antinutrients are compounds that interfere with nutrient absorption. Antinutrients can also and cause gastrointestinal discomforts such as bloating and gas. The term "antinutrient" is misleading as they have an effect only when consumed in extremely large quantities. Additionally, the fermentation process reduces antinutrients in food.20
Varieties
There are different varieties of natto, each distinguished by the fermentation process, the variety of soybean, and the soybean size. At an Asian market, you might see large, medium, and small natto for sale. Hikiwari natto is another variety that is widely known. Hikiwari is natto that has been pulverized before the fermentation process.
When It’s Best
Natto is available year round.
Storage and Food Safety
Natto can be stored for months in the refrigerator, where it continues to ferment. It should be covered with cheesecloth and stored in an airtight contain to maintain the food's moisture level. Natto can also be frozen. While natto can last a long time, there is a point when the beans start to go bad. When natto accumulates tiny white dots, it is time to throw it away.
How to Prepare
Natto lovers say that the flavor is an acquired taste. But those that enjoy this food say the extra effort is worth it. The food contains glutamate which the tongue perceives as umami. Umami is considered to be the fifth basic taste and is described as both satisfying and savory.
Most people don't eat natto alone. It is usually consumed on white rice. But some also eat the food on top of toast or pasta. It can also be added to foods including miso soup, salads, or other Japanese dishes such as tamagoyaki (omelet) or okonomiyaki (savory pancake).
Try adding ingredients to natto to enhance the flavor. When sold in Asian convenience stores, mustard and a special Japanese sauce are usually included. You can also add soy sauce, raw egg yolk, chives, green onion, sliced dry bonito, kimchi, wasabi, cheese, mayonnaise, seaweed, peppers, or tuna.
Natto aficionados recommend that you mix the beans thoroughly before eating. When it develops a sticky texture then it is ready to eat.
By Malia Frey, M.A., ACE-CHC, CPT
Malia Frey is a weight loss expert, certified health coach, weight management specialist, personal trainer​, and fitness nutrition specialist.
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Natto Nutrition Facts and Health Benefits [re: Mod vege]
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