When eating plant-based food, are you likely to be deficient in certain vitamins and minerals? This is a very common question, and there’s no ‘one-size-fits-all’ answer.

While vegans are generally health-conscious, it’s surprisingly easy to be an unhealthy vegan. Arguably we need to take better care of our nutrient intake than vegetarians or carnivores. But that doesn’t necessarily mean taking more supplements.

The key nutrients likely to be low are:

1. Vitamin B12

On a plant-based diet, B12 is the ever-elusive vitamin. Many claim that spirulina and chlorella are both high in B12, but this is a source of some controversy. Sometimes what appears as B12 is actually an ‘analogue’ – i.e. an ineffective form – and it can be very difficult to spot the difference. While the jury is still out, research has shown that chlorella is the most likely source of reliable B12 (1).

Still, to get enough from plant foods, and to be sure it’s genuine B12, is a little risky. Deficiency can lead to anaemia, and some other pretty nasty conditions. Most vegans, including ourselves, take a supplement. You can get your B12 levels checked via your GP if you’re concerned.

2. Vitamin D3

Vitamin D can be absorbed via sunlight. This is all well and good from late spring to early autumn, if you spend time outdoors in the middle of the day, with your limbs and face exposed. The amount you can absorb then depends on various factors, such as your skin colour, and the time you spend exposed (2). Other than that, in the UK at least, the quality of light is not sufficient to provide us with the vitamin D we need.

Carnivores can get plenty from meat and fish. Vegetarians can get it from eggs and dairy products. Mushrooms are about the best plant source, but levels are really quite low.

Most vegans, including ourselves, take a supplement. You can get your D3 levels checked via your GP.

3. Omega 3

Omega 3 and 6 are both essential in the diet – meaning our bodies can’t produce them – but there’s no official RDA for them. Healthy levels are more to do with the ratio between the two, rather than absolute figures.

In short, omega 6 tends to have an inflammatory effect on the body, and omega 3 an anti-inflammatory effect. Too much 6 can also further block the absorption of 3. Humans are thought to have evolved with a 1:1 ratio of 6 to 3, but in the typical Western diet it’s more like 16:1 (3). This is largely due to the increased consumption of processed oils, such as soy and corn oil.

More about omega oils »

The catch for vegans

Plant-based omega 3, as you’d find in flax, for example, is alpha-linolenic acid (LNA), which is harder for the body to process than the EPA and DHA most commonly found in animal products (4). If you don’t have enough B3, B6, magnesium and zinc, the process is even harder (5).

This is a tricky balance for vegans, as nuts and seeds tend to be higher in 6 than 3. So while flax, chia and hemp are good sources of 3, to offset the 6 you’re probably consuming from other things, you may want to consider taking a supplement.

As a plant-based alternative to fish and krill oil, marine algae oil is high in DHA and EPA. Fish don’t actually produce omega 3 anyway – the original source is marine algae, which is then ingested by fish. We take algae oil capsules.

More about marine algae oil »

4. Sulphur Amino Acids

Amino acids are basically the building blocks of protein. Some are essential, meaning the body can’t make them, so they have to be obtained through the diet or supplements.

If you’re getting plenty of protein from a variety of plant sources, you’re probably covering your RDA for most of these, but two are a little tricky to get: methionine and cysteine. These are sulphur amino acids (SAAs). Methionine is essential, and cysteine is considered ‘conditionally essential’, but some claim it’s in a special class of its own, and arguably it’s just as important (6).

Where can we get them?

From legumes, nuts, seeds and some grains; to a lesser extent from sulphur-rich vegetables such as brassicas (cabbage family), alliums (onion family) and mushrooms. Vitamins B1 (thiamin) and B7 (biotin) also contain sulphur. These plant sources combined may not give you enough to hit your RDA though, and if you have a very active lifestyle, you might need more than the RDA.

Why is sulphur so important?

It plays a major role in the way many other nutrients are processed by the body, and is required for protein synthesis. Especially of note to vegans is that it affects the absorption of B12 (7). Methionine can convert to cysteine, but neither can be stored by the body, so excess is either excreted or stored as glutathione (8). Methionine is really the cornerstone of sulphur in the body.

Should you take supplements?

Personally, if we can’t get sufficient quantities of a certain nutrient from food, we try to take supplements closest to the type found in what we eat. We therefore choose to supplement with methionine and cysteine.

Some people choose to take MSM (methylsulfonylmethane), which is a different sulphur compound, found naturally at low levels in vegetables, and which can convert to methionine. MSM is volatile in its natural state, so food is not a reliable source (9).

Other people take glutathione supplements. This can be useful for joint problems, especially as it converts to collagen, but relying on it too much for sulphur intake means the body might have to convert it back to cysteine.

Absorbing SAAs

You can help absorption by making sure you have enough vitamin C, selenium and B vitamins (so-called methylation nutrients) in your diet. Selenium can be a little tricky to get, but simply eating a couple of brazil nuts a day should do the trick for most people.

Other amino acids

Vegans will also naturally have low intake of the amino acids carnitine and taurine, but these are non-essential, meaning the body can make them. Cysteine converts to taurine anyway. Similarly your tyrosine intake might be a bit low, but as long as you’re getting enough protein overall, you should have enough phenylalanine to make tyrosine.

More about protein in legumes »

5. Iodine

Those eating the average UK diet probably get enough iodine (10), but if you’re health-conscious it’s actually a little more complicated.

  • Research shows that vegans are especially likely to be deficient (11). Iodine is naturally present in fish – originally from the algae they eat – and it’s also used in milk production. Vegans obviously won’t benefit from either of these sources. It’s possible to get iodine from fresh vegetables, but the amount largely depends on the quality of the soil they’re grown in, and it’s unlikely to be significant. Cooking further degrades iodine as well (12).
  • Most table salt is fortified with iodine. Sea salt and Himalaya salt will only have naturally occurring iodine, present only in small amounts. So if you’re using these in place of table salt (which is generally a good idea), or if you’re on a low-sodium diet, you won’t benefit from this source either.
  • Iodine levels can be further reduced by goitrogens, present in raw brassicas such as broccoli, cabbage and kale, as well as soy and flax – all popular ingredients on a plant-based diet. While cooking reduces goitrogens, as mentioned, it also reduces iodine levels.

The simplest way to add iodine to a plant-based diet is with seaweed. Seaweed is a powerful ingredient, to be used with care. Seek advice from a health practitioner if you have an existing medical condition. Only a very small amount should be needed to meet your RDA. Even if your health is good, it’s best to start with a small amount of cooked seaweed a couple of times a week, before increasing servings or incorporating it raw.

More about seaweed »

6. Iron

Some people struggle to get enough iron from a plant-based diet, even if the iron levels are technically okay in the foods they’re eating. Younger women (i.e. pre-menopausal) are particularly likely to have this problem.

Non-heme iron (as found in plants) is harder to absorb than heme iron (as found in meat), but an adequate intake of vitamin C can help.

Another complication is that antinutrients such as phytates, oxalates and tannins can bind to the iron in the diet, making it harder to absorb. Soaking pulses, lightly cooking greens, and roasting nuts can all help reduce this risk.

More about antinutrients »

It’s best to avoid supplementing iron if possible, instead trying to get enough from food, and perhaps boosting your vitamin C intake. If you accidentally take more than you need, it can block the absorption of other minerals, such as calcium and magnesium. Do get your levels checked though if you’re concerned about anaemia – your GP can do a blood test.

More about bioavailability »

7. Calcium

Calcium is fairly plentiful in green vegetables, but you’d struggle to eat enough of them alone to meet your RDA. You can also get it from nuts, seeds and soy, but still the level is likely to be a little low overall. Supplementation shouldn’t be necessary as long as you’re eating a really healthy and balanced diet, but your GP can test for it if you’re concerned.

Again, be careful not to take too much calcium though, as it can inhibit iron and magnesium absorption. Vitamin D helps calcium absorption, so be sure to hit your RDA for that too.

More about bioavailability »

Our experience

We’ve gone from one extreme to another in our own experiments with nutrients – first hoping we could get everything from food, then adding in a lot (really a lot) of supplements, based on various protocols we’ve read about.

Now we’re aiming for the middle way – looking in detail at the maximum we can get from our diet, and identifying any likely shortfalls. This has involved a nerdy process of:

  • Weighing and logging absolutely everything we eat in a 2-week period
  • Establishing the nutrient profile of each food (using the USDA database, as there’s no UK equivalent)
  • Establishing our RDAs for each nutrient
  • Putting it all into a graph by nutrient / food group

We eat about 70 different types of plant-based whole foods each week, and would struggle to do better than that. We’re hitting our RDAs for most nutrients, as we’d hope, but there are still a few even in our pretty strict regime that don’t quite make it. By tweaking our intake we’ve been able to fix some of them, but others were still a little way off: B12, D3, Omega 3, methionine and cysteine.

No perfect answer

Obviously the figures we used in our study are not going to be perfectly accurate. We don’t know the exact variety of a food measured in the USDA database, the soil conditions it was grown in, how old it was and how it was stored before testing – all of which can have an impact on nutrients. Also our diet is 100% organic, much of it homegrown or locally sourced, so we’d hope at least some of our levels would be a bit higher in reality. Added to that, we don’t know exactly how our bodies process each nutrient – we may need slightly more or less than the RDA. Every day will be different for each individual anyway, depending on environmental factors and what else is going on in the body. But it’s given us a good picture.

Where to go from here?

  • Consider getting blood tests from your GP to check levels of key nutrients: B9, B12, D3, calcium, iron and vitamin C. More in-depth tests are available privately, but this gives a good gauge of overall health if you’re concerned.
  • We believe it’s much better to get nutrients from real food whenever possible, than from isolated supplements. Try to eat plenty of fresh vegetables, fruit and other whole foods in as much variety as you can.
  • Consider ways you can get the most out of nutrients naturally found in your food.
    More about nutrient loss »
  • Certainly taking supplements is better than having a deficiency. For most of us, supplementing is probably a good idea – to a greater or lesser extent, depending on the diet and health of the individual. If you do take supplements, be aware that not all are plant-based, so shop carefully if you’re a strict vegan. Also try not to take a higher dose than you need, especially with things like calcium and iron.
  • If you’re curious about your intake, but don’t fancy poring over spreadsheets (and who could blame you?) there are more and more nutrition apps coming out these days. We haven’t found one we’d recommend, but this area is changing fast, so keep an eye out if you think it might be of interest.
  • Above all, don’t be discouraged. A plant-based diet can be super healthy, and has so many potential benefits – both for the individual and for the planet. It just takes a little thought and care to make sure you’re getting the most you can from your food. Rather than a restriction, it can be an adventure. Maybe challenge yourself to eat a rainbow of fresh produce in a day or in a meal. Buy a variety of vegetable you’ve never tried before. Have fun! 🙂

Got any tips or questions of your own about supplements on a plant-based diet? Leave us a comment below, we’d love to hear from you.


Nutrient bioavailability in a plant-based diet »
Are we losing nutrients in food preparation? »
Beans, Chickpeas & Lentils: do legumes have enough protein? »


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