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What are they? How can they be avoided?

Vegan diets can have many health benefits, but they may not contain all the necessary nutrients. To avoid a deficiency, a person should be sure to consume a variety of nutritious plant-based foods and consider taking supplements.

Unless a person plans their vegan diet very carefully, they may need to take supplementary vitamin B12 and iron. A person may also need supplementary vitamin D, iodine, and omega-3 fatty acids.

Below, we look into why vegan diets may not contain all the necessary nutrients. We also describe the symptoms of specific deficiencies and which plant-based foods and supplements can help.

A well-planned vegan diet is rich in fruits and vegetables and generally low in highly refined foods.

However, any diet that does not contain whole food groups may contribute to a lack of certain nutrients. Animal products can be rich sources of certain nutrients that are more difficult to derive from a plant-based diet.

For example, animal products are the only natural sources of vitamin B12, which helps maintain blood cells and prevent anemia.

Researchers have also found that levels of zinc, protein, selenium, and other nutrients are low in vegan diets.

However, consuming fortified foods and supplements can ensure that a person with a vegan diet is receiving sufficient nutrition.

Below, we describe symptoms of common deficiencies and strategies for tackling them.

Omnivorous diets typically contain enough B12 to meet most people’s needs. As vegan diets do not include animal products, vitamin B12 deficiencies may occur.

A cross-sectional analysis of participants with omnivorous, vegetarian, or vegan diets found that about half of the 232 vegan participants had vitamin B12 deficiencies. Compared with the other groups, the vegan group had the lowest overall levels.

According to the National Institutes of Health (NIH), most teenagers and adults need 2.4 micrograms (mcg) of vitamin B12 per day. This increases to 2.6 mcg or 2.8 mcg for people who are pregnant or breastfeeding, respectively.

Vitamin B12 deficiencies can cause symptoms that include:

  • tiredness
  • weakness
  • constipation
  • unexpected weight loss
  • a loss of appetite
  • tingling in the hands and feet
  • balance problems
  • difficulties remembering
  • soreness of the mouth and tongue
  • confusion
  • depression

In addition, a deficiency in vitamin B12 can cause megaloblastic anemia. This involves the bone marrow producing oversized, undeveloped red blood cells, leading to low red blood cell levels.

It can also occur from a deficiency in vitamin B9, also known as folate.

Some vegan foods are fortified with B12, but they may not provide enough. Taking a B12 or B complex supplement can help ensure a sufficient intake of this important nutrient. Anyone concerned about their B12 intake should speak with a healthcare provider.

Learn more about vitamin B12 here.

Omega-3 fatty acids contribute to heart and brain health.

Not getting enough omega-3s can also affect the skin, causing swollen, itchy rashes or scaly, dry patches.

The three main types of omega-3 are alpha-linolenic acid (ALA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA).

The body can convert ALA to DHA and EPA in very small amounts. For this reason, some people mainly focus on consuming ALA. However, the conversion rate is very low: Only 5–8% of ALA is converted into EPA and a maximum of 5% is converted into DHA.

As a result, it is crucial to consume sources of each omega-3. Plant-based foods that contain ALA include:

  • nuts, such as walnuts
  • seeds, such as chia or flaxseeds
  • plant oils, such as canola oil
  • fortified foods, such as cereals or juices

Focusing too heavily on ALA is also risky because if a person consumes too much linoleic acid, a type of fat concentrated in foods including canola and soybean oils and nuts and seeds, this further hampers the conversion of ALA to DHA and EPA.

Algae is one vegan source of DHA and EPA. It is currently unclear how much DHA and EPA are necessary for a healthy diet.

Learn more about omega-3s here.

The thyroid, a butterfly-shaped gland in the neck, converts iodine into thyroid hormones — triiodothyronine and tetraiodothyronine, known respectively as T3 and T4. These hormones help regulate crucial biological functions, such as metabolism.

The body does not produce iodine, so a person needs to get it from their diet. The recommended daily amount for adults is 150 mcg.

Having an iodine deficiency could lead to hypothyroidism. Symptoms include:

  • an inability to tolerate colder temperatures
  • fatigue
  • weight gain
  • a goiter

Learn more about hypothyroidism here.

Some vegan sources of iodine include:

  • iodized salt
  • soy milk
  • seaweed
  • cranberries
  • potatoes
  • prunes

If a laboratory test reveals an iodine deficiency, the person needs to take an iodine supplement.

Learn more about iodine here.

Iron is a mineral with several important functions throughout the body, including helping blood cells carry oxygen and supporting brain health.

Iron deficiencies may cause anemia, which restricts oxygen delivery to cells around the body.

Other symptoms of an iron deficiency include:

  • stomach problems
  • tiredness
  • weakness
  • difficulty concentrating or remembering
  • an increased susceptibility to infections

Heme iron is a form common in meats, fish, and eggs. The body easily absorbs it. Plant-based products contain nonheme iron, which is harder to absorb.

The NIH report that adult males typically require around 8 mg of iron per day and adult females require around 18 mg. But as nonheme iron is harder to absorb, people with vegan diets require around twice these amounts.

Plant-based sources of iron include:

  • nuts
  • some dried fruits, such as raisins
  • beans
  • lentils
  • spinach
  • peas
  • iron-fortified cereals

Learn more about iron here.

Some people require an iron supplement, especially females of childbearing ages.

Vitamin D helps absorb calcium for healthy bones and protect against chronic bone conditions, such as osteoporosis.

The body makes vitamin D from sun exposure. Few foods naturally contain the vitamin, but manufacturers fortify many products with it, including cereals and milk.

There are two main types of vitamin D: D2 and D3. Vitamin D3 boosts overall levels of the vitamin in the body higher and for longer than vitamin D2.

Animal products are the only natural source of vitamin D3, but vegan supplements are available. They use lichen as a source.

A person with a vegan diet can get D2 from supplements, mushrooms, and fortified foods.

Vitamin D deficiency is very common, and a person should get their levels checked with a blood test. Depending on the results, the doctor may recommend a supplement.

Learn more about vitamin D here.

Calcium is an important mineral for bone health and muscle functioning. A deficiency could increase the risk of problems such as osteoporosis or bone fractures.

Symptoms of a severe calcium deficiency include:

  • numbness or tingling in the fingers
  • abnormal heart rhythms
  • convulsions

Vegan foods that contain calcium include:

  • broccoli
  • brussels sprouts
  • collards
  • kale
  • mustard greens
  • chard
  • beans
  • peas
  • soy products

Fortified foods are also a source of calcium.

Learn more about calcium here.

Creatine is found in animal tissues, and it helps produce energy during exercise.

Vegan diets are typically lower in creatine than other diets. While creatine is not an essential nutrient, it can improve athletic performance.

Taking a synthetic, and thus vegan, creatine supplement may compensate for lower creatine stores in the muscles.

Learn more about creatine here.

For people with vegan diets, doctors often recommend supplements, including B12. It is a good idea to work with a knowledgeable healthcare provider, who can help develop a tailored plan to avoid nutritional deficiencies.

Having a more varied, targeted vegan diet can also account for low levels of certain nutrients. A healthcare provider can offer guidance about adapting the diet.

In general, it can also help to research nutritional contents when planning meals.

A vegan diet may not contain all the necessary nutrients, such as vitamin B12. A person can address these deficiencies by adjusting their diet and taking vegan supplements.

It is also worth noting that general nutritional information may not be tailored to people with vegan diets. For example, a person may need twice the recommended amount of iron because iron from plant-based sources is harder for the body to absorb.