B12 on a Plant Based Diet: What Actually Counts as a Source

Most nutrition advice for plant based diets comes with caveats and hedging. B12 does not. It is the one nutrient where the guidance is flat and unambiguous: if you eat no animal products, you need a reliable source, and food alone will not provide it.

Here is why, and what counts as reliable.

B12 does not come from plants or animals

This is the part that surprises people. B12 is not made by plants, and it is not made by animals either. It is made by bacteria.

Grazing animals get it because bacteria in their digestive systems produce it, and because they ingest soil bacteria along with grass. It accumulates in their tissues, which is how it reaches us through meat, dairy and eggs.

Humans do host B12 producing bacteria, but in the large intestine, which sits past the point where B12 is absorbed. So we produce some and cannot use it, which is an unhelpful piece of design.

Historically, humans also picked up B12 from unwashed produce and untreated water. Modern hygiene removed that route, which is a trade almost everyone would take, but it is worth knowing it happened.

What does not count as a source

A number of foods are widely believed to provide B12 and do not.

Spirulina and other algae contain compounds that look like B12 in older testing methods but are not biologically active in humans. They are called B12 analogues, and there is some evidence they may compete with real B12 for absorption. Spirulina is in our greens blend for other reasons, and we would not present it as a B12 source.

Fermented foods such as tempeh, miso and sauerkraut are inconsistent at best. Any B12 present depends on which bacteria happened to be involved.

Mushrooms are frequently cited and generally do not contain meaningful amounts.

Unfortified nutritional yeast contains none. Fortified nutritional yeast does, because B12 has been added. Check the packet, since both are sold and they look identical.

What does count

Fortified foods and supplements. That is the list.

Fortified plant milks, fortified breakfast cereals, fortified nutritional yeast and yeast extracts such as Marmite. Read the label, because fortification is not universal and some organic ranges specifically do not fortify.

The NHS guidance on B12 is clear that people who do not eat animal products need either fortified foods or a supplement.

Why deficiency creeps up slowly

The liver can store several years' worth of B12. That is useful and it is also the trap.

Someone who goes vegan may feel entirely fine for a long time while quietly running down a store built up over decades. By the time anything is noticeable, the shortfall has been running for a while. This is the reason the advice is to arrange a source from the start rather than wait to feel different.

It is also why "I have been vegan for two years and I feel great" is not evidence of anything about B12 either way.

Cyanocobalamin or methylcobalamin

Two forms turn up on labels, and the internet debates them more heatedly than the evidence justifies.

Cyanocobalamin is the most studied, the most stable and the form used in most fortification. Methylcobalamin is an active form, marketed as more bioavailable, and is less stable in storage.

For most people either works. Cyanocobalamin's stability is a genuine practical advantage in a product sitting on a shelf. Ours is cyanocobalamin, in the B complex.

The other three worth knowing about

B12 gets the attention, and three others deserve a mention on a plant based diet.

Iodine. In the UK, dairy is the dominant dietary source, because of cattle feed and dairy hygiene practice. Remove dairy and that source goes with it. Plant milks are not consistently fortified with iodine. Seaweed contains it but very unevenly, and kelp can deliver far more than intended. There is iodine in Daily Greens+ and naturally in Sea Moss.

Iron and zinc. Plant foods contain plenty of both, but non haem iron is absorbed less readily than the haem iron in meat, and phytates in wholegrains and pulses bind both. Vitamin C alongside plant iron improves absorption noticeably, which is a free and genuinely useful thing to act on. Lemon on the lentils.

Vitamin D. Not a plant based issue at all. Nobody in the UK makes vitamin D from October to March, so the winter advice applies to everyone.

The short version

• B12 comes from bacteria, not plants or animals directly
• Spirulina, mushrooms and fermented foods are not reliable sources
• Fortified foods or a supplement are the only dependable routes
• Liver stores last years, so feeling fine proves little
• Cyanocobalamin is the stable, well studied form
• Iodine deserves as much attention and gets almost none

Five of the six gummies in the daily GUUDIES pouch are vegan. Daily Greens+ carries B12 at 24µg and iodine at 38µg. Every dose is listed on the ingredients page.

This is general information rather than medical advice. If you think you may be low, ask your GP for a blood test rather than guessing.