While often recognized for its polarizing taste and sticky texture, the nutritional value of natto, a traditional Japanese fermented soybean dish, is undeniable. The fermentation process, which utilizes the Bacillus subtilis bacteria, dramatically enhances the beans' nutrient profile, most notably boosting its vitamin content to impressive levels.
The Vitamin Superstar: Vitamin K2 (Menaquinone-7)
Natto is considered the richest natural food source of vitamin K2, specifically the highly bioavailable and long-chain menaquinone-7 (MK-7). While many Western diets provide vitamin K1 from leafy greens, the fermented natto provides MK-7, which is better absorbed and remains active in the body for longer. A single 100-gram serving can contain hundreds of micrograms of vitamin K2, far exceeding the daily recommended intake.
Why is K2 So Important?
The high concentration of MK-7 in natto provides several significant health benefits:
- Bone Health: Vitamin K2 activates proteins like osteocalcin, which is responsible for binding calcium to the bone matrix. This process is crucial for increasing bone mineral density and strength, and research suggests it may reduce the risk of fractures, especially in postmenopausal women.
- Heart Health: K2 plays a vital role in directing calcium away from arteries and soft tissues, preventing arterial calcification. This keeps blood vessels supple and elastic, supporting overall cardiovascular health.
A Deep Dive into Natto's Complete Nutritional Profile
While its vitamin K2 content is the most remarkable, natto is a powerhouse of other essential vitamins and compounds:
- B Vitamins: The fermentation process increases levels of B vitamins. Natto is a good source of riboflavin (B2), which is important for energy metabolism and skin health, and contains other B vitamins like B6 and folate.
- Probiotics and Enzymes: The Bacillus subtilis bacteria that ferments the soybeans acts as a potent probiotic, promoting a healthy gut microbiome and aiding digestion. It also produces the enzyme nattokinase, which has been studied for its fibrinolytic (clot-dissolving) properties that support heart health and blood flow.
- Minerals: A 100-gram serving of natto is a rich source of vital minerals, including manganese, iron, and magnesium.
- Protein and Fiber: As a fermented soybean product, natto provides a high amount of plant-based protein and dietary fiber, which promotes satiety and digestive regularity.
How Natto's K2 Content Compares to Other Foods
Natto's MK-7 content is uniquely high, especially among plant-based foods. The following table highlights the difference compared to some other known sources of vitamin K2, using data from various nutritional analyses.
| Food Source (per 100g) | Primary Vitamin K2 Type | Estimated Vitamin K2 Content (µg) | Key Observation |
|---|---|---|---|
| Natto (fermented soybeans) | MK-7 | ~1000 | Richest dietary source of MK-7, particularly bioavailable. |
| Goose Liver Pâté | MK-4 | 369 | A rich animal-based source, but not MK-7. |
| Hard Cheeses (aged) | MK-9 | 76 | Varies significantly by type and aging process. |
| Egg Yolk (pasture-raised) | MK-4 | 15.5-32 | Content varies based on the chicken's diet. |
| Chicken (dark meat) | MK-4 | ~8.5 | Lower concentration than natto or liver. |
A Note on Taste, Texture, and Preparation
Natto's strong, pungent aroma and sticky, slimy texture can be challenging for those not accustomed to it. However, its unique umami flavor is prized by many. In Japan, it is often mixed with rice and seasoned with soy sauce, karashi (Japanese mustard), and green onions. For those new to the flavor, starting with smaller amounts and mixing it with other foods can help. The stringiness of the beans, which develops from stirring, is a sign of healthy fermentation.
Conclusion: The Nutrient-Dense Fermented Food
In conclusion, the answer to what vitamin is natto high in is definitively vitamin K2, specifically the highly potent MK-7 form. This exceptional nutrient, produced through the fermentation of soybeans, provides powerful support for bone and cardiovascular health. Beyond its K2 content, natto is a comprehensive superfood, delivering significant amounts of protein, fiber, probiotics, enzymes, and essential minerals. For those willing to acquire the taste, incorporating natto into a regular diet can offer a robust boost to overall health and wellness. For more details on the molecular mechanisms of vitamin K2, visit the National Institutes of Health.
