Does Lowfat Kefir Have K2? Understanding the Fat-Soluble Vitamin

December 22, 2025 •

4 min read

While vitamin K1 comes from plants, Vitamin K2 (menaquinone) is predominantly synthesized by bacteria, making fermented foods like kefir a potential source. The question is, does lowfat kefir have K2 in significant amounts, or is its production tied to the presence of fat during fermentation?

Quick Summary

Lowfat kefir contains a minimal amount of Vitamin K2, since this is a fat-soluble nutrient produced by bacteria during fermentation and is concentrated in the fat content.

Key Points

Limited K2 in Lowfat Kefir: While fermentation can produce Vitamin K2, lowfat kefir has a substantially lower amount compared to full-fat varieties due to the fat-soluble nature of the vitamin.
Fat-Soluble Vitamin: Vitamin K2 is fat-soluble and is best absorbed when consumed with dietary fat; hence, full-fat dairy is a better source.
Bacterial Synthesis: K2, or menaquinone, is synthesized by bacteria during the fermentation process, with the amount depending on the specific bacterial cultures used.
Fermentation Matters: A longer fermentation period with robust kefir grains can increase the production of menaquinones (Vitamin K2), but the fat content remains a key determinant of final concentration.
Varied Dietary Sources: For higher K2 intake, consider full-fat kefir, aged cheeses like Gouda, or natto (fermented soybeans), which is exceptionally high in K2.
Supports Bone Health: Vitamin K2 works synergistically with Vitamin D to direct calcium to the bones and away from arteries, a function that is more pronounced in K2 compared to K1.

The Science of Vitamin K2 Production in Fermented Foods

Vitamin K2 is a collection of compounds known as menaquinones (MKs), which are produced by certain types of bacteria during fermentation. In the context of dairy, bacteria used in mesophilic fermentation (room temperature) are particularly effective at producing K2, while thermophilic cultures (high heat, like many yogurts) produce very little or none. The kefir grain cultures, with their diverse and robust bacterial strains and yeasts, are known to be efficient at this process, creating various menaquinone forms like MK-7, MK-8, and MK-9. The specific menaquinone profile and quantity can vary widely depending on the starter culture, fermentation conditions, and length of the process. A 2017 study found that low-fat kefir contained 10.2 µg total vitamin K per 100g, while another 2019 study on Finnish kefir found lower levels, demonstrating this variability.

The Relationship Between Fat Content and K2

Vitamin K is a fat-soluble vitamin, which means it dissolves in fat and is absorbed most efficiently when consumed with dietary fat. Because of this, full-fat dairy products generally contain higher concentrations of K2 than their low-fat or skimmed counterparts. When milk is processed to become low-fat kefir, much of the milk fat, which is where the K2 would be concentrated, is removed. While the probiotic activity in low-fat kefir can still produce some K2, the final amount is significantly lower compared to a full-fat version. Some researchers even note that while some probiotic activity may produce K2, the fat content is the primary factor affecting the final concentration in the dairy product. This means that anyone seeking to maximize their K2 intake from kefir should opt for the full-fat variety.

How Fermentation Time and Culture Affects K2 Levels

The fermentation process is a dynamic one, and the resulting vitamin content is a direct reflection of the microbial activity. Studies have shown that K2 levels increase over the duration of fermentation as the bacterial population multiplies and works to produce menaquinones.

Longer fermentation: A longer fermentation period can lead to higher levels of K2, as the bacteria have more time to synthesize the compound. For example, a 15-hour kefir grain fermentation in a 2017 study was shown to have significantly higher MK-7 content than milk fermented for a shorter period.
Starter Culture: The type of bacteria in the kefir grains is critical. Different strains produce different menaquinones, some in higher quantities than others. Some commercial starter cultures may yield different results compared to traditional, live kefir grains. The most potent K2 sources, such as Japanese natto, use specific strains of Bacillus subtilis.

Other Good Sources of Vitamin K2

To increase your dietary intake of Vitamin K2, consider other food sources, particularly those that are fermented or rich in fat.

Natto: This Japanese fermented soybean dish is the single richest source of K2 (specifically MK-7), with significantly higher amounts than even full-fat dairy.
Hard and Soft Cheeses: Cheeses made with mesophilic cultures, such as Gouda and Brie, are excellent sources of longer-chain menaquinones like MK-8 and MK-9.
Animal Products: Animal products from grass-fed sources tend to have higher levels of MK-4. These include butter, eggs, and liver.
Sauerkraut: Some fermented vegetables contain K2 due to bacterial activity, though typically in lower concentrations than fermented dairy.

Comparison of K2 Content in Kefir and Other Foods


Food Type	K2 Content (µg/100g)	Notes
Full-Fat Kefir	Up to 13 µg	Variable, dependent on culture and fat content.
Low-Fat Kefir	Less than Full-Fat	Substantially lower; a 2017 study found ~10 µg total K, including other K vitamins.
Hard Cheese	30-80 µg	Good source of MK-8 and MK-9 from bacteria.
Natto	>1000 µg	Exceptionally high concentration of MK-7.
Chicken Breast	13 µg per 85g	Contains MK-4, though content can be lower.
Grass-Fed Butter	13-21 µg	Source of MK-4, with levels depending on diet.

Conclusion: Making an Informed Choice

So, does lowfat kefir have K2? The definitive answer is yes, but in a significantly lower quantity than full-fat kefir and other rich dietary sources like specific cheeses and natto. The production of Vitamin K2 is a function of bacterial fermentation, but its fat-soluble nature means it is primarily retained within the milk fat. For those looking to increase their Vitamin K2 intake, relying solely on lowfat kefir would be inefficient. A balanced approach would involve incorporating a variety of K2-rich foods into the diet, including full-fat fermented dairy, certain cheeses, and potentially natto, while also supporting overall gut health with probiotics. Consulting with a healthcare provider can help determine the best dietary strategy for individual needs, especially regarding the synergistic effects of vitamins D3 and K2. A balanced diet focusing on whole, fermented foods provides the best approach to ensuring adequate levels of this crucial nutrient for bone and cardiovascular health.

Evaluation of MENAQUINONE-7 and fat-soluble vitamin content...

Frequently Asked Questions

Yes, some Vitamin K2 is produced by bacteria during the fermentation process of kefir, even when using lowfat milk. However, the amount is substantially lower than in full-fat kefir because Vitamin K2 is fat-soluble and concentrates in the milk fat.

The primary reason is that Vitamin K2 is a fat-soluble vitamin. In full-fat kefir, the K2 produced by the bacteria during fermentation remains concentrated in the higher milk fat content, while this fat is mostly removed during the production of lowfat kefir.

While a longer fermentation period with kefir grains may increase the total K2 produced by the bacteria, the overall quantity will still be limited by the low fat content of the milk used. For higher K2 intake, using full-fat milk is more effective.

Excellent sources of Vitamin K2 include natto (fermented soybeans), specific types of cheese like Gouda and Brie, and some sauerkraut. Natto is considered one of the richest dietary sources of K2.

Yes, Vitamin K2 is known to play a crucial role in bone health by activating proteins that help with calcium metabolism. For optimal benefit, it is important to ensure a sufficient intake of K2, which may be more reliably achieved with full-fat kefir or other K2-rich foods.

Since Vitamin K2 is a fat-soluble vitamin, consuming it with a source of dietary fat will enhance absorption. This is why sources like full-fat dairy and grass-fed butter are more efficient at delivering K2 to the body.

Yes, there are different forms of Vitamin K2 known as menaquinones (MK-n). Kefir, especially when made with natural kefir grains, can contain a mix of these, including MK-7, MK-8, and MK-9, depending on the bacterial cultures present.