According to research reviewed by Gram, fermenting plant foods with Propionibacterium freudenreichii can generate vitamin B12 inside the food, and recent fungal-bacterial methods have reached levels more than ten times higher than earlier plant-based fermentations. However, no human trial has yet confirmed how well the body absorbs this vitamin, so these foods are not yet a proven source.
Vitamin B12 is essential for healthy nerves and blood, but it is found mostly in animal foods, which makes it harder for people on plant-based diets to get enough. A 2026 review published in Comprehensive Reviews in Food Science and Food Safety examined whether a bacterium called Propionibacterium freudenreichii, the microbe used to make Swiss cheese, could produce vitamin B12 inside plant foods during fermentation. According to research reviewed by Gram, recent experiments with fungal and bacterial partners have reached vitamin B12 levels more than ten times higher than earlier plant-based fermentations, which suggests the amounts may be nutritionally meaningful. The review also found that the body may absorb less of this vitamin from unprocessed fermented foods, and no human trial has yet tested how well it is absorbed. The approach is promising but still experimental.
Key Statistics
A 2026 review published in Comprehensive Reviews in Food Science and Food Safety found that recent fungal-bacterial fermentations produced vitamin B12 at concentrations more than ten times higher than earlier plant-based fermentations.
A 2026 review of the research found that no controlled human trial has yet measured how well the body absorbs vitamin B12 produced inside fermented plant foods.
A 2026 review reported that vitamin B12 bioaccessibility, meaning how much of the vitamin is released for digestion, was high in processed fermented products but substantially lower in unprocessed fermented material.
The Quick Take
- What they studied: Can fermenting plant foods with a common cheese-making bacterium produce enough vitamin B12 to help people who do not eat animal products?
- Who participated: This was a review of existing scientific papers, not a study with human volunteers. No people were enrolled, so there is no sample size to report.
- Key finding: Recent experiments combining fungi and bacteria in fermentation produced vitamin B12 levels more than ten times higher than earlier plant-based fermentations. The levels appear high enough to be nutritionally meaningful, but the review found that the body may absorb less of the vitamin from unprocessed fermented foods.
- What it means for you: Fermented plant foods are not yet a reliable source of vitamin B12. If you follow a plant-based diet, continue using proven sources such as fortified foods or supplements, and talk with a doctor or dietitian about checking your levels.
The Research Details
This paper is a review, which means the authors gathered and analyzed findings from many earlier studies rather than running a new experiment. They looked at how vitamin B12 is made by Propionibacterium freudenreichii, what conditions affect how much the bacterium produces, and how the approach has been applied to grains, beans, food byproducts, and other plant materials.
The authors also explained a key measurement problem. Common lab tests for vitamin B12 cannot tell the active form of the vitamin apart from similar molecules that the body cannot use. Because of this, the authors say that vitamin B12 levels reported in fermented plant foods need to be confirmed with more precise chemical methods before they are trusted.
Finally, the review considered whether the body can actually release and use the vitamin from these foods. It drew on laboratory digestion models, which simulate the stomach and intestines in a test tube, and noted that these models are not the same as testing in people.
A review is useful for pulling together scattered findings from many experiments into one picture. In this case, it shows that the basic science looks promising, while also identifying the gaps that still need to be filled before any health claims are made.
Because the review highlights measurement problems and the lack of human trials, it helps readers separate what has been shown in the lab from what has been proven to help people.
Reviews depend on the quality and number of the studies they include, and this one is focused on mechanisms and technology rather than systematic statistical pooling. The authors are open about what is unknown, which is a sign of careful reporting.
The main limitation is that most of the evidence comes from laboratory and pilot-scale work. The review itself notes that no controlled human trial has measured how much vitamin B12 from in situ fermentation the body actually absorbs, so the findings should be read as early-stage science.
What the Results Show
The review explains that vitamin B12 is made by Propionibacterium freudenreichii during fermentation, meaning the vitamin forms inside the food itself rather than being added afterward as a purified supplement. This could avoid some of the costly separation and purification steps used in industrial vitamin production.
The amount produced depends on several conditions. The most important include how much cobalt is available (cobalt is a trace mineral the bacterium needs to build vitamin B12), how well the food resists changes in acidity, how much oxygen is present, and which other microbes are grown alongside the bacterium. The authors describe these as the main levers for controlling yield.
One of the most encouraging points is that recent fungal and bacterial combinations have reached vitamin B12 concentrations more than ten times higher than earlier plant-based fermentations. The authors conclude that this suggests amounts sufficient for nutrition are achievable, though these results come from controlled settings rather than everyday food production.
The review also points to digestion as the bigger hurdle. In laboratory digestion tests, vitamin B12 was highly available in processed fermented products but much less available in unprocessed fermented material. The authors believe that breaking open the bacterial cells during processing is what releases the vitamin, so the way a food is prepared may determine how much the body can use.
The review notes that scaling up from small pilot projects to commercial production has not been solved. Costs and economic competitiveness also remain open questions, which matters because a fermented food must be affordable and practical to make at scale.
The authors also highlight that many published vitamin B12 numbers for fermented plant foods may not be reliable, because common lab methods can overestimate the active form. Confirming results with more precise chemical tests is therefore an important step for the field.
Vitamin B12 is well established as essential, and it is well known that animal foods are its main natural source. Fortified foods and supplements are the established ways to meet needs on plant-based diets, and this review does not challenge that guidance.
The idea of using microbes to make vitamins in food is also not new, since fermentation has long been used to produce other nutrients. What this review adds is a detailed look at how this specific bacterium could be used in plant foods and where the scientific gaps lie.
This is a review rather than a new experiment, so its conclusions depend on the quality of the earlier studies it summarizes. Many of those studies were done in laboratories or at small pilot scale, which may not reflect how foods are made and eaten every day.
The most important limitation is that no controlled human trial has yet measured how well the body absorbs vitamin B12 made through this fermentation. Until such trials are done, it is not possible to say how much of the vitamin people would actually use, or whether it would be enough to prevent deficiency.
The Bottom Line
Confidence is high that vitamin B12 is essential and that plant-based diets need a reliable source, such as fortified foods or supplements. Confidence is low that fermented plant foods can currently supply this need, because the vitamin’s absorption in people has not been tested. Readers should not treat fermented plant foods as a substitute for proven sources at this stage.
People who eat little or no animal food, including vegans and many vegetarians, should pay attention because this research may eventually provide new options. Food scientists and food companies working on fermentation may find the technical details useful. People who already eat animal products or take a vitamin B12 supplement do not need to change anything based on this review.
Based on the review, it will likely take considerable time before fermented plant foods can be recommended for vitamin B12. Human absorption trials, scale-up to commercial production, and cost testing all still need to happen. Any benefit to everyday diets is probably years away, and current guidance will not change until that evidence exists.
Frequently Asked Questions
Can fermented plant foods provide enough vitamin B12 for a vegan diet?
Not yet, according to a 2026 review. Fermented plant foods can reach vitamin B12 levels more than ten times higher than earlier methods, but no human trial has confirmed how much the body absorbs. Fortified foods and supplements remain the proven options for people eating plant-based diets.
What bacteria is used to make vitamin B12 in fermented foods?
Propionibacterium freudenreichii is the main bacterium studied for this purpose. It is the same microbe used to give Swiss cheese its holes and flavor. Researchers are also testing combinations with fungi, which have produced higher vitamin B12 levels than earlier plant-based fermentations.
Why might the body absorb less vitamin B12 from unprocessed fermented foods?
A 2026 review found that digestion release is a key limit. Vitamin B12 is locked inside bacterial cells, and processing that breaks these cells open appears to free the vitamin. Laboratory tests showed much lower availability in unprocessed fermented material than in processed products.
How much vitamin B12 do adults need each day?
Adults generally need about 2.4 micrograms of vitamin B12 per day, according to standard nutrition guidance. Animal foods are the richest natural sources. People following plant-based diets are typically advised to use fortified foods or supplements to meet this amount reliably.
Want to Apply This Research?
- Log every intake of vitamin B12 sources in the app, including fortified cereals or plant milks (note the vitamin B12 amount listed on the label), supplements (dose in micrograms), and any fermented plant foods you eat. Record these daily so you can see whether your total intake meets the recommended daily amount of 2.4 micrograms for adults.
- Set a daily reminder to check that your B12 source is included, such as a fortified food at breakfast or a supplement with a meal. Treat fermented plant foods as an extra food choice rather than your main source until research confirms their absorption.
- Review your logged B12 intake monthly and share the trend with your doctor during routine checkups. Ask your healthcare provider about periodic blood tests for vitamin B12 if you follow a plant-based diet, and update your app entries if your supplement or fortified food choices change.
This article summarizes a review of scientific research and is for general education only. The findings relate to laboratory and pilot-scale work, and no human trial has yet tested the vitamin B12 produced by this fermentation method. Do not change your vitamin B12 intake based on this information. If you follow a plant-based diet or have symptoms of deficiency, consult a doctor, registered dietitian, or other qualified health professional.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.