Vegan diets have become one of the most popular alternative ways of eating in the past decade, however they aren’t without potential nutritional concerns and long-term adherence issues.
I have written many articles previously over the years on the topic of potential nutritional inadequacy concerns related to vegan diet patterns and its interesting to see the latest research continue to confirm many of my beliefs.
After stumbling upon a recent updated systematic review on the nutritional adequacy of vegan diets, I thought it warranted an updated article covering this very topic.
Intake and adequacy of the vegan diet. A systematic review of the evidence
The systematic review of 48 studies published in 2021 concluded:
Following a vegan diet may result in deficiencies in micronutrients (vitamin B12, zinc, calcium and selenium) which should not be disregarded. 
The systematic review also found that:
Veganism is also associated with low intake of vitamins B2, Niacin (B3), B12, D, iodine, zinc, calcium, potassium, selenium.
Conditional Essential Nutrients (Taurine, Carnosine/Beta-Alanine, Creatine etc)
Basic essential nutrients such as Vitamin B12, Calcium and Zinc aren’t the only potential nutritional concerns associated with vegan diets.
Even conditional essential nutrients such as taurine, carnosine/beta-alanine, creatine, choline and so on, can become depleted under certain circumstances or in certain sub-groups of individuals with various health conditions.
These are some of the concerns I have with vegan diets and propose to its proponents such as vegan registered dieticians.
Whilst it may be fairly easy to compensate for “easier” to identify known basic nutrients such as Vitamin B12, Calcium, Zinc etc). It isn’t so easy to test for or identify conditional essential nutrient deficiencies such as taurine on a day to day basis clinically for most.
Take even creatine for example and the fact that the studies have found that:
Research indicates that vegetarian and vegan diets reduce muscle creatine stores. 
Now the above may be bad enough for a professional athlete wanting to compete at the highest level, but what about for an individual with mitochondrial disease who may already have issues surrounding creatine.
A diet pattern such as vegan which has the potential to further reduce muscle creatine stores is hardly likely going to be beneficial to these sub-groups such as those with mitochondrial diseases and this is where the blind recommendation that vegan diets are always optimal or superior for health has to be seriously questioned.
In this article we are going to look at some of the most common nutrient deficiencies associated with vegan diets according to the research.
1. Vitamin B12
The most immediate nutritional concern associated with vegan diet patterns is the complete lack of reliable dietary Vitamin B12 intake.
Vegan diets typically provide no reliable dietary intake of Vitamin B12, as most of the common dietary sources of B12 are typically of animal origin such as meat, eggs, dairy and seafood.
As such the general recommendation for vegans is to supplement with Vitamin B12 and/or consume additional fortified foods to compensate and ensure adequate B12 intake.
Vegans who do not supplement with B12 were found to be at especially high risk of deficiency from the research.
The literature over the past couple of decades has consistently found vegans to be at high risk of developing sub-optimal Vitamin B12 levels and have higher rates of clinical deficiency than both omnivores and lacto-ovo vegetarians, along with elevated levels of homocysteine as a consequence.
Subnormal vitamin B-12 status is prevalent (50%–70%) in vegetarians or vegans in Austria, Germany, Italy, Australia, India and China.
Metabolic vitamin B-12 deficiency is prevalent in vegetarians and, in particular, in vegans. 
Vitamin B12 deficiency can result in a variety of serious symptoms, some of which are irreversible if left untreated such as spinal cord degeneration.
Essentially Vitamin B12 deficiency can nullify many of the cardiovascular health benefits associated with eating plant-based diet patterns.
Vitamin B12 status in vegans according to the research is highly dependent on supplementation, which isn’t a straightforward topic either.
Whilst many healthy individuals may be able to maintain their B12 status with a cheap cyanocobalamin supplement or fortified food, there are individuals with genetic issues who may require direct intake of the active forms such as methylcobalamin and adenosylcobalamin.
2. Omega-3 Fatty Acid (DHA)
Vegans who don’t consume algae Omega-3 supplements, typically rely on short-chain ALA intake for endogenous production of long-chain omega-3 fatty acids such as DHA.
This issue is complicated further by the fact that some of the research finds conversion of ALA to DHA to be both “unreliable” and “restricted” in adults. 
Most studies indicate that plasma, serum, erythrocytes, adipose, and platelet levels of EPA and DHA are lower in VGNs than omnivores. 
The popularity of extreme low fat vegan diet patterns such as those promoted by Caldwell Esselstyn, John McDougall and co, which either purposely restrict total fat intake to potentially unhealthy levels i.e sub <10% of total calories or generally recommend to either restrict or remove overt fat rich plant-foods from the diet has significant potential to exacerbate essential fatty acid inadequacy.
It can be difficult enough for many vegans to obtain healthy essential fatty acid intake even whilst including a variety of plant-based fat rich foods such as nuts, seeds, avocado and coconut, let alone restricting or worse completely removing all of these foods from the diet.
VGNs may need an ALA increase of 2.2–4.4 g/day (or 1.1 g/day/1000 Kcals) depending on the amount of LA in the diet in order to achieve a 4:1 n-6:n-3 ratio, as well as a decrease of dietary LA if intake of LA is higher than recommended. 
Good plant-based sources of Omega-3 fatty acid (ALA) include walnuts, flax and chia seeds, plant-based oils such as canola and even leafy greens.
Additionally vegans can supplement with Algae DHA oil supplements to provide intake of long-chain Omega-3 fatty acids(EPA and DHA).
Iodine is another potential micronutrient that can be of concern with strict vegetarian diet patterns such as vegan.
Most of the common dietary sources of Iodine tend to be of animal origin such as dairy, seafood and eggs for example. Removing these foods can result in inadequate Iodine intake.
However, Iodine deficiency doesn’t have to be an issue with vegan diets, sea vegetables such as Kelp, Dulse and Nori are an excellent concentrated plant-based source of the mineral Iodine.
Iodine is an essential trace element and an integral component of thyroid hormones. Deficiencies in Iodine can cause hypothyroidism.
Numerous studies have now found sub-optimal Iodine intake and low Iodine status to be common in vegans.
The systematic review concluded:
Vegans appear to have increased risk of low iodine status, deficiency and inadequate intake compared with adults following less restrictive diets.
Adults following vegan and vegetarian diets living in countries with a high prevalence of deficiency may be more vulnerable. 
4. Calcium & Vitamin D
Vegans have shown higher risk of fractures from research and lower markers of bone health such as bone mineral density, this may be in part related to inadequate intake of nutrients such as Calcium and Vitamin D.
Non-meat eaters, especially vegans, had higher risks of either total or some site-specific fractures, particularly hip fractures. 
Compared with omnivores, vegetarians and vegans had lower BMD (bone mineral density) at the femoral neck and lumbar spine and vegans also had higher fracture rates. 
Good plant-based sources of Calcium include Soy foods (Tofu etc), various low-oxalate leafy green vegetables such as Broccoli, Kale, Turnip Greens, Chinese Cabbage, Bok Choy, Tahini, Oranges and fortified foods such as Calcium enriched plant-based milks.
However, calcium bioavailability is inversely proportional to the amounts of oxalate, and to a lesser extent, to phytate and fiber found in plant-foods.
Vitamin D aids in the absorption of Calcium and Phosphorus, playing an essential role in bone health.
Whilst the majority of Vitamin D comes from sun exposure, supplementation may be necessary for many to maintain a healthy Vitamin D status. An additional dietary boost of Vitamin D can also help safe-guard against deficiency.
The few rare dietary sources of Vitamin D are typically of animal-origin such as oily fish(sardines, mackerel etc), liver, egg yolks and fortified foods such as breakfast cereals
Mushrooms which are exposed to a source of ultraviolet (UV) radiation such as sunglight can generate nutritionally relevant amounts of vitamin D according to the research. 
Vegans have shown the lowest zinc intake when compared to groups with different dietary habits such as omnivores.
Animal foods such as red meat, fish and poultry are some of the most common dietary contributors of the mineral zinc in the typical omnivorous diet.
Zinc from animal sources also tends to be more bioavailable than sources of plant-origin.
Dietary zinc intakes and serum zinc concentrations were significantly lower (-0.88 ± 0.15 mg day(-1), P < 0.001 and -0.93 ± 0.27 µmol L(-1), P = 0.001 respectively; mean ± standard error) in populations that followed habitual vegetarian diets compared with non-vegetarians.
Secondary analyses showed greater impact of vegetarian diets on the zinc intake and status of females, vegetarians from developing countries and vegans. 
Intake of both Zinc and Calcium was recorded as the lowest in vegan populations compared to non-vegan individuals. 
Good plant-based sources of Zinc include wholegrains such as oats, tofu, tempeh, legumes, nuts and seeds(pumpkin seeds) and fortified foods.
The information in this article has not been evaluated by the FDA and should not be used to diagnose, cure or treat any disease, implied or otherwise.
Always consult with a qualified healthcare professional before making any significant dietary or lifestyle changes including supplements and herbs.