Is There Vitamin K in Fermented Rice? The Surprising Nutritional Boost Explained

November 29, 2025 •

3 min read

Studies have shown that the availability of micronutrients like B complex, vitamin K, and iron increases drastically during food fermentation. This raises the question: is there vitamin K in fermented rice, and what factors influence its nutritional content?

Quick Summary

Yes, fermented rice contains vitamin K, specifically the K2 variant, which is synthesized by bacteria during the fermentation process. This method also enhances other nutrients like B vitamins and probiotics, improving overall gut health and nutrient absorption.

Key Points

Contains Vitamin K2: The fermentation process introduces vitamin K2 (menaquinone) into rice through the activity of bacteria like Bacillus subtilis.
Enhanced Nutrients: Fermentation drastically increases the bioavailability of micronutrients, including B vitamins, iron, calcium, and potassium, compared to plain rice.
Probiotic-Rich: Fermented rice is an excellent source of probiotics, which restore healthy intestinal flora and improve gut health.
Improved Digestibility: The process breaks down complex starches and anti-nutrients, making the rice easier to digest and promoting better nutrient absorption.
Immune System Boost: A healthy gut, supported by the probiotics in fermented rice, is vital for a strong immune system.
Natural Body Coolant: Fermented rice is known in many cultures for its ability to help cool the body during hot weather.
Traditional Health Food: Revered for centuries for its health benefits, fermented rice is a low-cost, nutritious dietary staple in many regions.

What is Fermented Rice?

Fermented rice is a traditional dish prepared by soaking cooked rice in water for a period, typically overnight. This process, known as lactic acid fermentation, is driven by naturally occurring or added microorganisms, such as Lactobacillus and Bacillus species, which break down starches and other compounds. The resulting food has a tangy flavor and a significantly altered nutritional profile compared to its unfermented counterpart.

The Fermentation Process and Vitamin K2

There are two main forms of vitamin K: K1 (phylloquinone), found in plants, and K2 (menaquinone), which is predominantly produced by bacteria. Raw rice contains negligible amounts of vitamin K, but the fermentation process can introduce and increase vitamin K2 content. Unlike vitamin K1, which is found in leafy greens, vitamin K2 is a fat-soluble vitamin created through microbial synthesis.

Certain bacterial strains, particularly Bacillus subtilis (the same bacteria used to make natto), are known for their ability to synthesize menaquinones, the compounds that make up vitamin K2. As these beneficial bacteria thrive in the fermented rice, they actively produce vitamin K2, which becomes part of the final product. The concentration of vitamin K2 can vary depending on the specific microbes involved and the length of the fermentation period.

Nutritional Comparison: Plain vs. Fermented Rice

While cooked rice provides energy and some basic nutrients, fermentation elevates its nutritional status to a new level. The process breaks down anti-nutrients like phytates, which normally hinder mineral absorption, thereby increasing the bioavailability of essential minerals. Below is a general comparison of nutritional aspects.


Nutrient Aspect	Cooked (Plain) Rice	Fermented Rice
Probiotics	Absent	Rich in beneficial bacteria like Lactobacillus
Vitamin K	Trace amounts (K1)	Contains significant amounts of K2
B Vitamins	Moderate levels; can be fortified	Enhanced levels of B6 and B12
Minerals	Limited bioavailability due to phytates	Increased bioavailability of iron, calcium, and potassium
Digestibility	Can be hard to digest for some	Easier to digest; beneficial for gut lining

Beyond Vitamin K: Other Fermentation Benefits

The health benefits of fermented rice extend far beyond its vitamin K2 content. The lactic acid bacteria generated during fermentation transform the food into a probiotic powerhouse, which can help restore healthy intestinal flora and aid digestion. This probiotic effect can alleviate common digestive issues like bloating, indigestion, and constipation. Furthermore, the process increases the antioxidant content, providing anti-inflammatory and anti-diabetic properties. Fermented rice also acts as a natural body coolant, making it a popular dish in hot climates.

Fermented Rice vs. Other K2-Rich Foods

While fermented rice is a good source of vitamin K2, other fermented foods are even more potent. Natto, a Japanese dish made from fermented soybeans, is widely regarded as one of the richest sources of vitamin K2 (MK-7). Other dairy-based fermented products like kefir and hard cheeses also contain notable amounts of vitamin K2. For those who do not consume natto or dairy, fermented rice offers a valuable, if less concentrated, plant-based source of this important vitamin.

For additional nutritional insights on fermented foods, a report on Menaquinones, Bacteria, and Foods offers a more detailed analysis.

Conclusion

In conclusion, the answer to "is there vitamin K in fermented rice?" is a resounding yes. Through the action of beneficial bacteria, the fermentation process synthesizes vitamin K2 (menaquinones), significantly enriching the nutritional value of cooked rice. This transformation not only adds a potent form of vitamin K but also boosts other micronutrients like B vitamins and minerals. Fermented rice is a highly digestible, probiotic-rich food that supports gut health, immunity, and overall well-being. While other foods may contain higher concentrations of K2, fermented rice remains an accessible and traditional method for naturally enhancing nutrient intake.

Frequently Asked Questions

The type of vitamin K found in fermented rice is primarily vitamin K2 (menaquinones), which is synthesized by the bacteria involved in the fermentation process.

Fermentation increases nutrients by breaking down complex compounds and anti-nutrients, making minerals like iron and calcium more bioavailable and introducing beneficial bacteria that produce B vitamins and vitamin K2.

Yes, some studies show that fermentation can increase the bioavailability of iron in rice by a significant amount compared to cooked rice.

Yes, fermented rice is a great source of natural probiotics, such as lactic acid bacteria, which are essential for maintaining a healthy gut microbiome.

To make fermented rice, soak cooked rice in water, cover it, and let it sit at room temperature for 8 to 24 hours. The beneficial microbes will multiply and begin the fermentation process.

For maximum probiotic benefit, fermented rice should be consumed at room temperature or cold, as heating it can kill the beneficial bacteria.

Yes, the probiotics in fermented rice can aid digestion by restoring healthy gut flora, which can help alleviate problems like bloating and constipation.