Natto's Unrivaled Vitamin K2 Content
Natto's status as a 'superfood' is primarily due to its exceptionally high vitamin K2 content, produced during the fermentation process by the Bacillus subtilis natto bacteria. While the exact amount can vary between batches, brands, and testing methods, most sources indicate that 100g of natto provides a remarkably high dose. Studies from different research groups show figures ranging from approximately 850 µg to over 1,200 µg per 100g. This is overwhelmingly in the form of menaquinone-7 (MK-7), a form known for its high bioavailability and long half-life in the body, which makes it particularly effective for health benefits.
The Source of the K2 Powerhouse
The transformation of plain soybeans into natto is what unlocks this vitamin K2 concentration. The Bacillus subtilis natto bacteria feast on the soybeans during fermentation, and in the process, they synthesize large quantities of menaquinone, primarily MK-7. This bacterial activity is what makes natto so nutritionally distinct from other soy products like tofu or edamame, which do not contain significant levels of K2. The sticky, stringy substance characteristic of natto is a direct result of this microbial fermentation and is where much of the beneficial nattokinase enzyme is also found.
Factors Affecting Vitamin K2 Levels in Natto
While natto is consistently an outstanding source of vitamin K2, the exact amount can fluctuate. Several factors play a role in determining the final concentration:
- Bacterial Strain: The specific strain of Bacillus subtilis used for fermentation has a significant impact on K2 production levels. Some strains are more efficient producers than others, leading to variability in different commercial products.
- Fermentation Conditions: Environmental factors like temperature, aeration, and time can influence the bacteria's metabolic activity and, consequently, their K2 synthesis. For instance, more optimal conditions can lead to higher yields.
- Raw Materials: The quality and type of soybeans used can also play a role. The initial nutrient composition of the soybeans provides the substrate for the bacteria, so differences here can trickle down to the final product.
- Production Method: Whether the natto is produced on a commercial scale or in a smaller, traditional manner can also affect consistency and final vitamin levels.
The Importance of MK-7 for Health
The high concentration of menaquinone-7 (MK-7) in natto is particularly important because it is highly effective at promoting bone and heart health. Its long half-life means it remains active in the bloodstream for a longer period compared to shorter-chain K2 forms like MK-4. This allows MK-7 to be effectively transported to and utilized by tissues throughout the body, including bone and blood vessels.
Health Benefits of Natto's K2:
- Bone Health: Vitamin K2 is crucial for bone mineralization. It activates osteocalcin, a protein that binds calcium to the bone matrix, promoting stronger, denser bones and reducing fracture risk, especially in post-menopausal women.
- Cardiovascular Health: K2 helps regulate calcium, preventing its buildup in soft tissues like arteries. This helps inhibit arterial calcification, a major risk factor for heart disease.
- Other Potential Benefits: Emerging research suggests roles for K2 in supporting other areas like cognitive function and immune health, although further study is needed.
Comparing K2 Content: Natto vs. Other Foods
Natto is in a league of its own when it comes to vitamin K2 content, especially MK-7. This comparison table illustrates just how significant the difference is between 100g of natto and 100g of other common K2 sources. The values for MK-7 are particularly noteworthy.
| Food (100g) | Primary K2 Form | K2 Content (µg) | Notes |
|---|---|---|---|
| Natto | MK-7 | 850–1,280+ | Highest natural source, rich in MK-7. |
| Goose Liver Pâté | MK-4 | ~369 | Rich animal source, high in MK-4. |
| Aged Hard Cheese | MK-9 (various) | ~76 | Variable content, contains different menaquinones. |
| Egg Yolk (USA) | MK-4 | ~15.5 | Lower levels, primarily MK-4. |
| Butter | MK-4 | ~15 | Animal source, depends on K1 content in animal feed. |
A Note on Dietary Intake and Balance
While natto provides a massive amount of K2, it's important to consider the overall diet. Vitamin K1 (phylloquinone), found in leafy green vegetables, is also essential and primarily involved in blood coagulation. The high dose of K2 from natto works in conjunction with other dietary nutrients, including Vitamin D and Calcium, to support optimal health. Individuals on blood-thinning medications like warfarin should consult a healthcare provider, as consistent intake of high vitamin K foods is critical for medication management. For most healthy individuals, a small daily portion of natto can easily meet or exceed suggested dietary intake levels for K2.
Practical Considerations for Natto Consumption
For those new to natto, its strong flavor and sticky texture can be challenging to adjust to. However, its nutritional benefits make it worth exploring. It is commonly served with rice and soy sauce, but can also be incorporated into a variety of dishes. Some find that stirring it vigorously for a minute or two enhances its texture and can improve the experience. For a comprehensive overview of how MK-7 specifically affects bone, the research of PubMed is an excellent resource.
Conclusion
In summary, 100 grams of natto is an exceptionally concentrated source of vitamin K2, delivering over 850 micrograms primarily in the highly bioavailable MK-7 form. This high concentration is a direct result of the fermentation process using Bacillus subtilis bacteria. The variability in K2 content is influenced by factors such as the bacterial strain, fermentation conditions, and raw materials. Natto’s potent MK-7 content offers significant benefits for bone density and cardiovascular health, distinguishing it from all other dietary sources. For anyone looking to dramatically boost their vitamin K2 intake, natto provides an unparalleled and natural food-based solution.
