💎 Key Nutrients
What Is Natto? Origin and Varieties
Natto is a traditional Japanese fermented soyfood with a long culinary history dating back to at least the Edo period (1603–1868) where it became a staple breakfast food in Japan. Its name derives from the Japanese word “nattō” and is characterized by its distinctive sticky, stringy texture and powerful aroma that develop through fermentation with the bacterium Bacillus subtilis var. natto. This fermentation not only transforms the taste and texture of soybeans but also enhances their digestibility and nutrient profile. Unlike plain cooked soybeans, natto carries unique biochemical profiles, including beneficial peptides, enzymes (such as nattokinase), and living bacterial cultures that are responsible for many of its purported health benefits. Natto’s texture and flavor can vary slightly depending on soybean size and variety, regional fermentation practices, and fermentation duration, but the core sensory traits remain consistent: a strong, earthy aroma, a nutty umami flavor, and a stringy, viscous consistency when stirred. Historically, fermented foods like natto were developed as methods of food preservation before refrigeration, leveraging microbial action to extend shelf life while adding new flavors. Today, natto remains deeply rooted in Japanese food culture where it is traditionally served atop steamed rice often garnished with soy sauce, mustard, scallions, or raw egg. Outside Japan, natto is proliferating in global markets through health food stores and Asian groceries, prized for its nutrient density and functional food properties. Contemporary varieties may include additions of mixed grains or seeds, but traditional natto remains purely fermented soybeans. As a living food, natto is also a topic of scientific interest not just as a food but as a potential functional ingredient in broader nutritional and medical research. Its fermentation process increases the availability of certain nutrients and introduces probiotic bacteria that contribute to the gut microbiome’s composition, setting it apart from unfermented legumes such as cooked soybeans or tofu.
Nutrition Profile: A Detailed Breakdown
Natto’s nutrient profile is notable among legume products for its combination of high protein, fiber, beneficial fats, and micronutrients. According to USDA FoodData Central, a 175 g serving (~1 cup) of natto contains 211 calories, 19.4 g of protein, 11.0 g of total fat, 12.68 g carbohydrates, and 5.4 g dietary fiber. This makes it a nutrient-dense food, particularly among plant-based proteins. The protein content in natto is significant for plant foods: at nearly 20 g per serving, it delivers a robust amino acid profile including essential amino acids like leucine and valine which are critical for muscle protein synthesis. Compared to tofu or cooked soybeans, natto often has a higher level of bioavailable amino acids due to partial proteolysis during fermentation. On fats, natto contains predominantly unsaturated fatty acids, including monounsaturated and polyunsaturated fats, which are linked to heart health when replacing saturated fats. Natto also contains essential fatty acids including some omega‑3 and omega‑6 precursors, albeit in modest amounts compared to fatty fish or seeds. Carbohydrates in natto are relatively modest, with roughly 12.68 g, and ~4.89 g total sugars, none of which are added sugars, making it compatible with lower‑sugar diets. Micronutrient‑wise, natto is particularly rich in vitamin K (especially as menaquinone‑7 or MK‑7), which plays a key role in bone metabolism and blood clotting pathways. Although the USDA data reports ~23.1 µg per cup, fermented natto is widely recognized as one of the richest food sources of vitamin K2 in the diet, which occurs during fermentation. It also provides iron (8.6 mg), potassium (729 mg), calcium (217 mg), magnesium (115 mg), and trace elements like zinc and selenium. These minerals contribute to electrolyte balance, enzyme function, and antioxidant defenses. The fiber content supports digestive health and helps modulate blood glucose when consumed with carbohydrate‑rich foods. Vitamin C (13 mg) and B vitamins are present in modest amounts, adding to the overall nutrient picture. When compared to other soy products like tofu or tempeh, natto often has higher levels of certain micronutrients and unique bioactives due to fermentation, including live cultures that add probiotic value beyond basic nutrition.
Evidence-Based Health Benefits
Scientific interest in natto has expanded beyond traditional knowledge to include multiple lines of research pointing to potential health benefits. One of the most investigated areas is bone health: habitual natto consumption elevates serum levels of MK‑7, a form of vitamin K2, which enhances osteocalcin carboxylation—an indicator of bone formation and mineralization. Meta‑analyses of observational and quasi‑experimental studies (N = 2,327) have found that regular natto intake is associated with significantly higher serum MK‑7 and modestly higher bone mineral density compared to lower or non‑consumers. This suggests that natto could support skeletal health, particularly in populations at risk for osteoporosis. Another clinical area centers on gut health and bowel movement regulation; a recent randomized, double‑blind, placebo‑controlled study with 30 healthy adults found that 3 g of natto powder consumed daily for four weeks significantly improved bowel movements and reduced discomfort during defecation compared to placebo, suggesting beneficial effects on intestinal function and microbiome interactions. The probiotic nature of Bacillus subtilis var. natto introduced in natto may help diversify gut microbial communities, contributing to improved digestion and reduction of pathogenic bacteria. Cardiovascular health is another promising area, particularly through the action of nattokinase, an enzyme produced during fermentation that exhibits fibrinolytic activity (the ability to break down fibrin in blood clots). While most evidence derives from in vitro and animal studies or small human trials, nattokinase has been shown to support healthy blood lipid profiles, potentially lower blood pressure, and reduce arterial plaque formation. In one preclinical atherosclerosis model, natto‑derived B. subtilis modulated systemic immune responses relevant to atherogenesis, suggesting possible mechanisms for cardio‑metabolic benefits. Additional animal studies indicate that natto can favorably alter gut microbiota and metabolites to prevent diet‑induced hyperlipidemia. Beyond these areas, natto also contains soy isoflavones and peptides that exert antioxidant and anti‑inflammatory effects in preclinical models, contributing to cellular health and possibly reduction of chronic disease risk. Collectively, these benefits tie back to specific compounds such as MK‑7, nattokinase, probiotics, fiber, and soy phytonutrients—each of which plays a role in cellular processes linked to cardiovascular, digestive, and bone health.
Potential Risks and Who Should Be Careful
Despite its nutrient density and potential benefits, natto isn’t universally appropriate for everyone. The high fiber and fermented content can cause digestive discomfort—bloating, gas, or changes in bowel habits—particularly in individuals who are not accustomed to high‑fiber diets. Those with soy allergies should avoid natto entirely, as soy is one of the eight major food allergens and can trigger severe reactions. Additionally, because natto is rich in naturally occurring vitamin K, individuals on anticoagulant medications (e.g., warfarin) need to monitor intake closely, as vitamin K can antagonize the action of these drugs and affect clotting factors. People with a history of kidney stones may need personalized guidance due to natto’s potassium and mineral load. Another consideration is taste and sensory sensitivity; the strong aroma and sticky texture may be off‑putting for some, leading to over‑reliance on supplements rather than whole food. While research points to cardiovascular benefits from nattokinase, high‑dose enzymatic supplements are distinct from whole food intake and may carry different safety profiles; individuals with bleeding disorders or on antiplatelet therapies should consult healthcare providers before use. There’s also ongoing debate about soy phytoestrogens in specific populations, such as those with estrogen‑sensitive conditions, though current evidence generally supports the safety of moderate soyfood consumption within a balanced diet. In sum, natto is safe for most people but requires caution for those with allergy, medication interactions, or specific medical conditions.
How to Select, Store, and Prepare Natto
To select high‑quality natto, look for packages with firm, intact sealed containers and a pleasant, slightly fermented aroma (not sour). Commercial natto is typically refrigerated and should feel cold to the touch. Avoid packages with excessive liquid separation or strong off‑odors, which can indicate spoilage. Fresh natto is available in most Asian grocery stores; frozen versions may also be found but can alter texture upon thawing. For storage, keep unopened natto refrigerated at 34–40°F (1–4°C) and use within 3–5 days of purchase. Once opened, consume within 2–3 days if kept chilled, keeping the container airtight to minimize exposure to oxygen. Freezing is feasible if fresh natto won’t be used within a few days; freeze in airtight containers for up to 2–3 months, though texture may become slightly more watery upon thawing. Always check for spoilage signs like strong sour smell, discoloration, or sliminess beyond its natural texture before consuming. When preparing natto, minimal heat preserves probiotics and enzymes; traditionally it’s stirred vigorously to enhance stringiness, then served cold atop hot steamed rice. Additions like soy sauce, mustard, scallions, or sesame seeds complement its savory taste. For cooking, add natto at the end of soups or warm dishes to retain beneficial compounds. If raw fermentation tastes are too intense, start with mixtures in sushi rolls, salads, or blended into sauces to acclimate the palate. Ultimately, proper selection, storage, and gentle preparation preserve natto’s nutritional and functional qualities.
Best Ways to Eat Natto
Natto’s versatility extends beyond a traditional Japanese breakfast. Nutritionally optimal ways to consume natto emphasize minimal heating to retain probiotics and enzyme activity. The most common and culturally authentic method is to serve natto atop warm steamed rice with condiments such as soy sauce, karashi mustard, and finely chopped scallions. This preserves its live cultures while balancing flavor. For those who want to integrate natto into Western meals, stirring natto into cool salads, grain bowls, or vegetable wraps adds a protein‑rich fermented element that enhances gut health. Bolder eaters can incorporate natto into miso soups by adding it at the end of cooking to preserve probiotics. Natto also pairs well with soft scrambled eggs, avocado toast, or blended into pesto or dips. Some chefs recommend pairing natto with citrus or vinegar‑based dressings to cut through its earthy aroma. Smoothies are not typical due to texture, but blending small amounts with complementary flavors like banana and cocoa can work for nutrient boost. From a nutrition preservation standpoint, eating natto raw or gently warmed allows for the greatest retention of its unique bioactives such as nattokinase and probiotic bacteria. For those aiming to increase bone health support, pairing natto with vitamin D‑rich foods like mushrooms or fortified milk can enhance calcium utilization. Athletes might combine natto with whole grains and leafy greens to optimize amino acid uptake and micronutrient balance. Overall, natto’s earthy, umami flavor can be adapted into a variety of dishes while preserving its nutrient density and functional benefits.
Nutrient Absorption: What Helps and Hinders
Nutrient absorption from natto can be enhanced by pairing it with foods that provide complementary nutrients. Vitamin K2, abundant in natto, works synergistically with vitamin D and calcium to promote bone health; consuming natto with vitamin D sources (e.g., sunlight exposure, fortified foods) can optimize this effect. The fermentation process also breaks down complex proteins and fibers into smaller, more digestible components, increasing amino acid absorption. Probiotic bacteria present in natto promote gut diversity, which can improve overall nutrient uptake and short‑chain fatty acid production, which supports colon health. However, compounds like phytates found in soy can bind to minerals such as iron and zinc, potentially inhibiting their absorption. Fermentation reduces phytate levels compared to unfermented soy products, but pairing natto with vitamin C‑rich foods (e.g., citrus fruits or peppers) can further enhance iron absorption. Conversely, consuming high amounts of caffeinated beverages with meals may hinder iron absorption due to polyphenol interactions. Sodium intake should be moderate; while natto itself is low in sodium, added condiments like soy sauce can increase sodium load and may influence blood pressure regulation in sensitive individuals.
Natto for Specific Diets
Natto aligns well with several dietary patterns. In vegan and vegetarian diets, it provides a complete plant protein source along with B‑vitamins, minerals, and beneficial fats. Its fermented nature also supports gut health within plant‑based eating. For low‑carb and ketogenic diets, natto’s carbohydrate content (~12.68 g per cup) requires moderation, but its high fat and protein make it a suitable occasional inclusion. Paleo adherents may value natto’s minimal processing, though some paleo frameworks limit legumes. In diabetic‑friendly diets, natto’s fiber and protein help modulate blood glucose when eaten with complex carbohydrates. For heart‑healthy diets, the unsaturated fat profile, fiber, and nattokinase activity align with recommendations to support cholesterol and blood pressure regulation. However, condiment choices (e.g., high‑sodium sauces) should be mindful. Those with gastrointestinal sensitivities may need to introduce natto gradually due to its fermentation and fiber content.
❤️ Health Benefits
Supports Bone Health
Increases serum vitamin K2 (MK‑7) which enhances osteocalcin activation and bone mineralization.
Evidence: ModerateImproves Digestive Regularity
Fermentation produces probiotics that support gut microbiota balance and bowel movement consistency.
Evidence: PreliminaryMay Support Cardiovascular Health
Nattokinase exhibits fibrinolytic activity that may help maintain healthy blood lipids and blood pressure.
Evidence: Preliminary⚖️ Comparisons
Vs. Tofu
Natto has more probiotics and vitamin K2 due to fermentation versus tofu’s higher water content.
Vs. Tempeh
Both are fermented soy foods, but natto generally provides more vitamin K2 and a stronger probiotic profile.
Vs. Cooked Soybeans
Natto offers enhanced digestibility and unique enzymes from fermentation not found in plain cooked soybeans.
🧊 Storage Guide
❄️
Fridge
3–5 days
🧊
Freezer
2–3 months
⚠️ Signs of
Spoilage:
- smell: strong sour odor beyond natural fermentation smell
- visual: significant discoloration, excessive liquid separation
- texture: slimy beyond natural stickiness
- when to discard: mold growth, off‑odor persists
👥 Special Considerations
elderly
Why: Vitamin K2 and protein support skeletal maintenance.
Recommendation: Beneficial for bone health
athletes
Why: Provides amino acids and micronutrients for recovery.
Recommendation: Include as part of balanced protein intake
children
Why: High fiber and strong flavor may cause digestive upset.
Recommendation: Introduce small amounts gradually
pregnancy
Why: High vitamin K but soy allergens and fermentation require monitoring.
Recommendation: Consume in moderation with prenatal guidance
breastfeeding
Why: Probiotics may benefit gut but monitor infant tolerance.
Recommendation: Moderate intake
🔬 Detailed Nutrition Profile (USDA)
Common Portions
1.00 cup
(175.00g)
| Nutrient | Amount | Unit |
|---|---|---|
| Water | 55.0200 | g |
| Energy | 211.0000 | kcal |
| Energy | 883.0000 | kJ |
| Protein | 19.4000 | g |
| Total lipid (fat) | 11.0000 | g |
| Ash | 1.9000 | g |
| Carbohydrate, by difference | 12.6800 | g |
| Fiber, total dietary | 5.4000 | g |
| Total Sugars | 4.8900 | g |
| Calcium, Ca | 217.0000 | mg |
| Iron, Fe | 8.6000 | mg |
| Magnesium, Mg | 115.0000 | mg |
| Phosphorus, P | 174.0000 | mg |
| Potassium, K | 729.0000 | mg |
| Sodium, Na | 7.0000 | mg |
| Zinc, Zn | 3.0300 | mg |
| Copper, Cu | 0.6670 | mg |
| Manganese, Mn | 1.5280 | mg |
| Selenium, Se | 8.8000 | µg |
| Vitamin C, total ascorbic acid | 13.0000 | mg |
| Thiamin | 0.1600 | mg |
| Riboflavin | 0.1900 | mg |
| Niacin | 0.0000 | mg |
| Pantothenic acid | 0.2150 | mg |
| Vitamin B-6 | 0.1300 | mg |
| Folate, total | 8.0000 | µg |
| Folic acid | 0.0000 | µg |
| Folate, food | 8.0000 | µg |
| Folate, DFE | 8.0000 | µg |
| Choline, total | 57.0000 | mg |
| Vitamin B-12 | 0.0000 | µg |
| Vitamin B-12, added | 0.0000 | µg |
| Vitamin A, RAE | 0.0000 | µg |
| Retinol | 0.0000 | µg |
| Carotene, beta | 0.0000 | µg |
| Carotene, alpha | 0.0000 | µg |
| Cryptoxanthin, beta | 0.0000 | µg |
| Vitamin A, IU | 0.0000 | IU |
| Lycopene | 0.0000 | µg |
| Lutein + zeaxanthin | 0.0000 | µg |
| Vitamin E (alpha-tocopherol) | 0.0100 | mg |
| Vitamin E, added | 0.0000 | mg |
| Vitamin D (D2 + D3), International Units | 0.0000 | IU |
| Vitamin D (D2 + D3) | 0.0000 | µg |
| Vitamin K (phylloquinone) | 23.1000 | µg |
| Fatty acids, total saturated | 1.5910 | g |
| SFA 4:0 | 0.0000 | g |
| SFA 6:0 | 0.0000 | g |
| SFA 8:0 | 0.0000 | g |
| SFA 10:0 | 0.0000 | g |
| SFA 12:0 | 0.0000 | g |
| SFA 14:0 | 0.0310 | g |
| SFA 16:0 | 1.1680 | g |
| SFA 18:0 | 0.3930 | g |
| Fatty acids, total monounsaturated | 2.4300 | g |
| MUFA 16:1 | 0.0310 | g |
| MUFA 18:1 | 2.3990 | g |
| MUFA 20:1 | 0.0000 | g |
| MUFA 22:1 | 0.0000 | g |
| Fatty acids, total polyunsaturated | 6.2100 | g |
| PUFA 18:2 | 5.4760 | g |
| PUFA 18:3 | 0.7340 | g |
| PUFA 18:4 | 0.0000 | g |
| PUFA 20:4 | 0.0000 | g |
| PUFA 20:5 n-3 (EPA) | 0.0000 | g |
| PUFA 22:5 n-3 (DPA) | 0.0000 | g |
| PUFA 22:6 n-3 (DHA) | 0.0000 | g |
| Fatty acids, total trans | 0.0000 | g |
| Cholesterol | 0.0000 | mg |
| Tryptophan | 0.2230 | g |
| Threonine | 0.8130 | g |
| Isoleucine | 0.9310 | g |
| Leucine | 1.5090 | g |
| Lysine | 1.1450 | g |
| Methionine | 0.2080 | g |
| Cystine | 0.2200 | g |
| Phenylalanine | 0.9410 | g |
| Tyrosine | 0.5560 | g |
| Valine | 1.0180 | g |
| Arginine | 0.9090 | g |
| Histidine | 0.5120 | g |
| Alanine | 0.7980 | g |
| Aspartic acid | 1.9560 | g |
| Glutamic acid | 3.3370 | g |
| Glycine | 0.6460 | g |
| Proline | 1.4030 | g |
| Serine | 1.1210 | g |
| Alcohol, ethyl | 0.0000 | g |
| Caffeine | 0.0000 | mg |
| Theobromine | 0.0000 | mg |
Source: USDA FoodData Central (FDC ID: 172443)
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