8 Nutrient deficiencies to be aware of on a vegan or vegetarian diet

More often than not, people turn to vegetarian or vegan diets for ethical or environmental reasons. Usually, in my experience, I tend to find that they are unaware of all (not just iron and B12) the potential nutrient deficiencies that can commonly occur on these diets, which can lead to serious health issues in the long term such as fatigue, mood/cognition issues, hormonal imbalances, poor immunity, joint/bone problems, skin conditions and digestive issues. If you have read that all of your nutrient requirements can come from plants alone, you have been severely misguided by unscientific information.

Thankfully in the age of supplementation and food fortification, a vegan or vegetarian diet is possible, without suffering health effects. One just has to recognise that if you remove animal products, you have to add something back in to make up for those lost nutrients.

Often people just jump into this new lifestyle, without understanding the impact that it can have on their health. Because of their lack of dietary knowledge they don’t realize that they could be damaging their bodies, which might only become prevalent a few years down the track.

Now before we dive in, let’s just clear up some terminology first.

What are vegetarian and vegan diets?

A vegetarian diet is where an individual avoids animal foods such as meat, seafood and fish. Although some vegetarians will eat fish. Vegetarians tend to eat foods from animal origin such as dairy and eggs, however some may not. Some may also include fish. Vegans on the other hand tend to avoid all animal based foods and foods that are of animal origin. Therefore, these diets are usually based around vegetables, fruit, grains, beans, legumes, plant derived oils, nuts, seeds, processed meat substitutes and processed food. As mentioned above, the reasons behind these dietary choices are usually for ethical and environmental reasons, however some vegans/vegetarians advocates further claim to say that a diet without animal products is in fact healthier, which as I will show below, is not supported.

Nutrient deficiencies in vegan and vegetarian diets

When examining diet and nutrition it is always good to look at it from two angles, one is from an evolutionary perspective, and the second is from modern epidemiological and clinical evidence. Most nutrition claims in mainstream media fail on both fronts. The evolutionary perspective is important because it informs us about what a natural human diet really is.

For 66,000 generations, since we discovered fire cooking, humans ate primarily meat and fish, wild fruits and vegetables, nuts and seeds, and some starchy tubers and plants. It was likely that the addition of animal foods made our brains bigger due to their nutrient density.

There were some differences, of course, in the ancestral diets geographically. The Inuit typically have a very high-fat diet and low carbohydrate intake because of the limited availability of plant foods in that part of the world, whereas people like the Qatabans and Tukisenta in the South Pacific, where fruit and starchy tubers like sweet potatoes are readily available, tended to eat a high percentage of calories as carbohydrate.

But despite those differences, the ancestral human diet shared a lot in common. They weren’t eating processed and refined foods, and they also weren’t vegetarians or vegans.

In fact, no human population in the history of civilization has ever been recorded surviving on a vegan diet, and again, that alone should tell you something. There are few, if any, known human populations that even followed a vegetarian diet exclusively, and if they did it was usually not by choice. They would often go to great lengths to trade with other local peoples for prized animal foods, for example.

As you can see, from an evolutionary perspective, a vegan diet is not exactly natural, as it is lacking in nutrients that are essential to our health (e.g. B12). A diet where you have to supplement to get certain nutrients to make it work, should never be considered an optimal diet.

Now from an epidemiological and clinical evidence perspective, vegans and vegetarians tend to suffer more from certain nutrient deficiencies when compared to omnivores, even if they are eating high amounts of nutrient dense plant foods. Although some plant products have similar amounts of nutrients when compared to animal based foods, scientific evidence shows that the nutrients in animal products are more bioavailable (i.e. more absorbable) to the body.

These nutrients include iron, zinc, calcium, vitamins A and D, DHA/EPA as well as protein. In the western world it is uncommon for severe nutrient deficiencies to occur due to supplements, food fortification and food abundance, however vegetarians and vegans due to their dietary choices are at greater risk of nutrient deficiencies below the optimal level.

Lastly, another thing worth pointing out is that vegetarians and vegans usually find their protein sources from extremely carb dense food like grains, which can lead to issues with insulin and weight gain.

Vitamin B12

A study using the most sensitive B12 testing techniques (HOLO-TC) in humans showed that 68% of vegetarians are deficient in B12 and 83% of vegans are deficient.

This is because B12 does not exist in plant foods, it exists in meats, eggs, fish and dairy. Therefore without supplementation, a person who avoids animal products is likely to be deficient. There is a common misconception that B12 can be obtained from spirulina, yeast, seaweed and soy, however these foods contain B12 analogues called cobalamides, which block true B12 absorption in those foods.

In saying this, there are some processed foods like cereals, which contain fortified B12, however obtaining B12 from refined carbohydrates may not be the healthiest option.

If you are eating liberal amounts of fish, seafood, dairy and eggs consistently, then a B12 supplement is likely to be unnecessary. However, if you are not consuming these foods consistently, then I would suggest supplementing with 1,000mcg of a B12 supplement that contains B12 in the form “methyl-cobalamin.” It’s the most absorbable form.


 While leafy greens like spinach and kale have relatively high calcium content, the calcium is not efficiently absorbed during digestion.

Calcium is often deficient in vegans and vegetarians who avoid dairy. This is because calcium bioavailability in plant foods is very low due to the presence of oxalates and phytic acid, which are plant chemicals that inhibit the absorption of calcium. While leafy greens and spinach are said to have high amounts of calcium, due to oxalates and phytic acid, a lot of the calcium is not absorbable to the body.

Therefore, it would take approximately 16 servings of spinach (33 cups) to get the same amount of absorbable calcium as a glass of milk. That would be 33 cups of [raw] baby spinach, or around five to six cups of cooked spinach. This is standard for most plant based sources of calcium, where large servings of plant based calcium rich foods are needed to achieve the same amounts of absorbable calcium when compared to dairy products like milk, yoghurt and cheese. Therefore, it is very difficult to meet daily calcium needs with only consuming plants.

It must be noted that within all foods, including animal foods, nutrients work in synergistic relationships where some enhance the absorption of other nutrients, while others inhibit the absorption. For example, calcium, zinc, magnesium and iron compete for similar absorption transporters in the gut, therefore in food, they can competitively inhibit one another.

If you are not consuming eggs, dairy and seafood consistently, then it would be good to supplement with 500 mg of calcium. Ideally this would be supplemented along with vitamin D, as these nutrients share a close relationship. This will be discussed below.


Although vegetarians often have similar iron intakes to omnivores on paper from plant foods, it is more common for them and especially vegans to be iron deficient. Why? Because iron in animal products, such as red meat and liver, is called heme iron, and it is far better absorbed and assimilated than ferrous, or non-heme, iron found in plant foods like spinach, beans/legumes and kale.

Also, these sources of iron have low bioavailability due to the presence of phytic acid and oxalates, which inhibit iron absorption. Therefore, similarly to calcium, a person has to consume multiple servings of iron rich plant foods to get the same amount of absorbable iron that are found in smaller servings of animal foods.

Lastly, the absorption of non-heme, or plant-based, iron is inhibited by several commonly consumed substances such as coffee, tea, and dairy products because of their calcium and supplemental fiber. But none of these substances with the exception of calcium has a significant effect on the absorption of heme iron from animal products.

Supplementing with iron can sometimes be dangerous due to toxicity; therefore I would consult a doctor before looking to go on any iron supplements. However, in general, when supplementing with iron, try to find supplements that contain 15-30mg of “ferrous biglycinate,” as this is the most absorbable form of iron that will not cause constipation. Only supplement if there is a deficiency, otherwise concentrate on eating plant foods that are high in iron such as beans, legumes, leafy greens, nuts and seeds.


Zinc is highest in meat, eggs and seafood. This is why vegetarians and vegans tend to be deficient. Overt zinc deficiency is not often seen in Western vegetarians, but their intake often falls below recommendations. This is another case where bioavailability is a factor. Many plant foods that contain zinc (e.g. pumpkin seeds and nuts) also contain phytic acid, which inhibits zinc absorption.

The lack of bioavailability of zinc, iron and calcium in plant foods means that even when the diet meets or exceeds the recommended daily intake for these nutrients, deficiency may still occur.

Supplementing with 25-45mg per day with the most bioavailable form of zinc called zinc biglycinate, is necessary for most vegetarians and certainly vegans.


Plant foods such as nuts (walnuts), flax seeds/flax oil and chia seeds contain alpha-linolenic acid, which is a type of an omega-3 fatty acid. An increasing body of research has highlighted the benefits of the long-chain omega-3 fatty acids, however these benefits mostly come from the active forms of omega-3, which are EPA & DHA. These fatty acids are primarily found in fish, seafood, fish oils and algae, which is why vegetarians and vegans are more likely to be deficient.

While it is possible for some alpha-linolenic acid from plant foods to be converted into the active omega-3’s (i.e.. EPA & DHA), that conversion is poor in humans: between 5-10% for EPA and 2-5% for DHA. Moreover, the conversion of ALA to DHA depends on zinc, iron and B6, which are nutrients that vegetarians and vegans are less likely than omnivores to get enough of.

This probably explains why vegetarians have 30 percent lower levels of EPA and DHA than omnivores, while vegans have 50 percent lower EPA levels and nearly 60 percent lower DHA levels.

Marine algae supplements are a great way for vegans and vegetarians who don’t consume fish, to get their EPA and DHA. These supplements also contain high amounts of nutrients such as iodine, magnesium, and calcium, while containing low amounts of toxicants like mercury and PCB. Also, due to the issue of overfishing, algae supplements are also a great way of getting omega-3’s without damaging our earth. 1-2g of DHA and EPA from an algae supplement would be sufficient on a vegan and vegetarian diet.

Vitamin A and D

These two important fat-soluble vitamins are mainly found in animal foods such as seafood, organ meats, eggs and dairy products.

Both vitamins are particularly hard to get from the diet because they are mainly both found in significant amounts within organ meats like liver. Fish is also a great source of vitamin D.

Vitamin D does exist within plant foods. In fact, there are some obscure species of mushrooms that can provide large amounts of vitamin D, but these mushrooms are rarely consumed and they’re pretty difficult to obtain. This explains why vitamin D levels are 58 percent lower in vegetarians and 74 percent lower in vegans than in omnivores.

Similar to ALA (as mentioned above), it is poorly converted to the biologically active form of vitamin D in the body.

Also, the idea that plant foods contain vitamin A is a common misconception. Plants contain beta-carotene, a phytochemical that has its own health benefits, which is the precursor to active vitamin A (retinol). While beta-carotene is converted into vitamin A in humans, the conversion is inefficient.

For example, a single serving of liver per week would meet the RDA of 3000 IU of retinol. To get the same amount from plant foods, you’d have to eat two cups of carrots, one cup of sweet potatoes, or two cups of kale every day.

Supplementing 1-3,000 IU of a vegan friendly vitamin D and 10,000 IU of vitamin A per day should be sufficient to maintain adequate levels of these nutrients in the body.  When seeking a vitamin D supplement, try to find one that also contains calcium.


Plant foods that contain relatively high amounts of protein are beans, legumes and wholegrain. The first issue with plant protein sources is that they are not complete protein sources. This means they don’t contain all (or contain small amounts) of the essential amino acids. Essential amino acids can’t be synthesised by the body, therefore they must come from the diet. They are extremely important as they are the building blocks of proteins in our body. This is with the exception of soy, amaranth, buckwheat and quinoa.

Therefore protein combining in vegetarian and vegan diets are often necessary, in order to ensure all essential amino acids are consumed. For example, most beans and legumes are low in the essential amino acids called methionine and high in lysine, while grains like rice are low in lysine and high in methionine. This means that combining both of these foods throughout the day, will ensure an individual gets all essential amino acids.

The second issue about plant proteins is that they are less bioavailable compared to animal proteins. Most animal protein is 90-100% absorbed by the body, where as many vegetarian sources of protein are around 60-70%.

These are the reasons why vegetarians and vegans lack adequate amounts of protein in their diet. Also, their protein sources are usually in the form of carbohydrate sources, which can lead to weight gain and issues with insulin.

To ensure adequate protein intake, make sure you are consuming a combination of beans, legumes and peas, along with grains. Also protein powders are a great way to increase protein intake. There are a number of vegetarian and vegan friendly protein powders that can be added to smoothies.

Lastly, in people who ingest animal products that are high in protein, the stomach is forced to produce stomach acid because stomach acid is essential for digesting protein. Therefore, if you are not eating a lot of high protein foods, your stomach acid production will decrease. This is why when vegetarians/vegans try to switch over to an animal based diet after being a vegetarian/vegan for a while, they struggle to digest meat. When they eat meat, it feels like a brick is sitting in their stomach.

Low stomach acid is also an issue because it is part of our immune system and it helps kill harmful bacteria in our food before it gets to our intestines. Therefore, with low stomach acid, harmful microbes can move into the intestines and cause bacterial overgrowth (i.e. dysbiosis and SIBO), which can lead to IBS symptoms like food intolerances and digestive issues like gas, bloating, stool issues, reflux, heartburn and cramping. This then leads to even more restriction in these individuals’ diets because they end up having food intolerances.

If vegan/vegetarian diets cause nutrient deficiencies, then why do some people feel better on a vegetarian/vegan diet?

Adding more whole foods like fruits and vegetables into anyone’s diet would make them feel better and healthier. People who transition to a vegan or vegetarian diet may feel a lot healthier, because they moved away from a nutrient-void diet full of processed foods. Therefore there is nothing intrinsically special about a vegetarian/vegan diet, it’s just that a person tends to eat more whole foods.

Individuals who adhere to a whole food vegetarian and vegan diet tend to eat more fiber, magnesium, vitamin C, carotenoids and B9 compared to omnivores as these foods are high in plant foods, but they may run into the nutrient deficiencies listed above. Also, there are many vegetarians and vegans who eat a lot of processed food that don’t contain animal products, however they are not exactly health promoting.

Can omnivores suffer from these nutrient deficiencies?

It goes without saying that omnivores are also prone to these nutrient deficiencies due to a lack of intake as well as other factors that may affect nutrient absorption in ALL humans, vegan or not. These include stress, age, gut issues, increased alcohol intake, certain medication use, as well of iron loss through bleeding.

 Ok that is all well and good, but don’t animal foods like meat and eggs cause diseases like cancer? And don’t vegans and vegetarians live for longer?

 All too often in the mainstream media, we hear completely exaggerated claims about the negative health effects of animal products like meat, dairy and eggs.

However, these claims are usually made from a biased perspective using poor evidence (or even no evidence at all), misinterpreting/misreporting scientific data and cherry-picking information that is not consistent with scientific literature.

The reason for these misguided claims are because studies that examine the health effects of meat consumption and health (e.g. cancer rates) are observational/correlational in nature. This means that researchers draw a correlation (association) between meat consumption and disease rates of people.

However, what people always fail to realise is that correlation does not mean causation. Yes meat is “correlated” with cancer rates, however it is well known that meat eaters tend to smoke more, eat less fruit and vegetables, exercise less and do other “unhealthy” behaviours that lead to disease rates. Because these studies are correlational, they can’t control for all of the confounding variables that may affect the results. Trying to control these variables would mean that researchers would have to lock people up in metabolic wards for many years and the only thing that would differ, would be whether they ate meat or not. As you can see, there are slight ethical issues here.

Also, those studies don’t differentiate between red meat consumption from a Maccas burger with processed carbs and refined oils, the same as red meat from a grass fed cow, consumed with vegetables. As you can see, context is key here.

Lastly, these studies ask people to record their “average” red meat intake over a few months to a few years, however it is well known that humans are notoriously bad at remembering what they ate. Think about it, can you even remember what you ate for dinner last week, or 2 months ago?

Vegans and vegetarians are also more likely to engage in other “health promoting behaviours,” which is why they are subject to the “healthy user bias” in these studies. Ultimately, these types of studies should compare vegans and vegetarians to omnivores that eat a balanced, whole food diet.

Take away

When it really comes down to it, all of the different fad diets may focus on eating different foods and different macros, but ultimately, they try to encourage the consumption of more, whole unprocessed foods, which is the most important thing when it comes to nutrition.

People should endeavour to eat a balanced diet of whole-foods containing both animal and plant products. People who do this, have been shown to be healthier than those who don’t. In the same way that a meat-based diet is healthier with a little bit of plants, a plant-based diet is healthier with a little bit of animals.

And if you chose to be a vegan or vegetarian, make sure that you supplement appropriately and eat plant foods high in the nutrients that you would normally get from meat.

Lastly, even including some fish, meat and eggs every so often can go a long way (ethically sourced). By doing this it still means that you are decreasing your overall consumption of animal products and it is much less than the average person.


Here are some other reasons as to why a vegan diet may not work for an individual but discussing these things are beyond the scope of this blog post:

– FODMAP intolerance

– histamine intolerance

– athletes

– people under high physical and emotional stress (nutrient deficiencies exacerbate mental health issues and make a person less robust)

– a vegan diet may cause and exacerbate chronic health issues