Natto: The Unquestionable Vitamin K2 Champion
Natto, a traditional Japanese dish made from fermented soybeans, is widely recognized as the single best dietary source of vitamin K2. The fermentation process, which utilizes the bacterium Bacillus subtilis, generates a uniquely high concentration of menaquinone-7 (MK-7), a highly bioavailable form of vitamin K2. Studies show that 100 grams of natto can contain over 1,000 micrograms (mcg) of vitamin K2, far surpassing any other food source. While its sticky texture and pungent aroma can be challenging for some Western palates, its nutritional value is undeniable. The high MK-7 content is particularly beneficial due to its long half-life, meaning it stays active in the body longer than other forms of vitamin K2.
Fermentation and K2 Content
The amount of vitamin K2 in fermented foods is not uniform. For example, while natto is exceptionally high in K2, other fermented foods like sauerkraut and kimchi contain significantly lower levels, though they still offer gut health benefits. This difference is directly related to the specific bacteria used during fermentation. The Bacillus subtilis strain used for natto is a highly efficient producer of MK-7, making it a standout among all fermented options.
Goose Liver: The Top Animal Source of MK-4
While natto dominates the MK-7 category, animal products are the primary source of menaquinone-4 (MK-4), another important form of vitamin K2. Among animal-derived foods, goose liver pâté stands out with an exceptionally high vitamin K2 content. Research indicates that 100 grams of goose liver pâté can contain approximately 369 mcg of vitamin K2, all in the MK-4 form. While this is less than the concentration found in natto, it is still a potent source, particularly for those seeking dietary MK-4.
The Importance of Grass-Fed Sources
For other animal products, the vitamin K2 content varies significantly based on the animal's diet. Eggs, chicken, and beef from grass-fed animals tend to have higher levels of MK-4 compared to those from conventionally raised animals fed a grain-based diet. This is because animals convert the vitamin K1 found in grass into K2. Therefore, choosing pasture-raised and grass-fed options is crucial for maximizing vitamin K2 intake from animal sources.
A Comparison of High Vitamin K2 Foods
To illustrate the difference in vitamin K2 potency, the following table compares key dietary sources based on their approximate content per 100 grams. Content varies based on preparation and sourcing.
| Food Source | Primary K2 Form | Approximate K2 Content (per 100g) |
|---|---|---|
| Natto (fermented soybeans) | MK-7 | 998–1,100 mcg |
| Goose Liver Pâté | MK-4 | ~369 mcg |
| Aged Hard Cheese (e.g., Gouda) | MK-8, MK-9 | ~76 mcg |
| Soft Cheese (e.g., Brie) | MK-8, MK-9 | ~57 mcg |
| Chicken Thigh (with skin) | MK-4 | ~53–60 mcg |
| Egg Yolk (pasture-raised) | MK-4 | ~15–32 mcg |
| Grass-fed Butter | MK-4 | ~15 mcg |
| Chicken Liver (pan-fried) | MK-4 | ~12.6 mcg |
| Ground Beef (grass-fed) | MK-4 | ~7 mcg |
The Health Benefits of Vitamin K2
Adequate vitamin K2 intake is essential for several critical bodily functions beyond just blood clotting. Its primary function is to activate specific proteins that regulate calcium deposition. This has profound implications for both bone and heart health. In bones, K2 activates osteocalcin, a protein that directs calcium to bone tissue, improving bone mineral density and reducing fracture risk. Conversely, K2 activates Matrix Gla Protein (MGP), which prevents calcium from accumulating in soft tissues, such as arteries and blood vessels. This dual action helps prevent vascular calcification, a major risk factor for cardiovascular disease.
Incorporating Vitamin K2 into Your Diet
For those not accustomed to natto, increasing vitamin K2 intake can be achieved through a varied diet. Incorporating grass-fed dairy products like butter and aged cheeses, as well as pasture-raised eggs and organ meats like chicken liver, can provide valuable amounts of the MK-4 form. For MK-7, while natto is king, some smaller amounts can be found in other fermented foods. Pairing these fat-soluble vitamin sources with a healthy fat, like olive oil, can also enhance absorption.
Conclusion: Which Food Has the Highest Vitamin K2?
In summary, natto contains the highest amount of vitamin K2 per serving, primarily in the potent MK-7 form. However, for those with dietary restrictions or aversions to natto's strong flavor, other excellent sources are available. Goose liver pâté is the most concentrated animal source of the MK-4 form, while other choices like grass-fed butter, aged cheese, pasture-raised eggs, and chicken liver offer significant amounts as well. Both the fermented MK-7 and animal-based MK-4 forms provide crucial benefits for bone density and cardiovascular health, making a balanced approach the ideal strategy for optimizing vitamin K2 intake. A diverse diet incorporating both fermented foods and high-quality animal products can ensure you receive ample amounts of this essential nutrient.
Visit PubMed Central for more detailed research on the functions and health benefits of Vitamin K2.
