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by Guest Author June 29, 2016 9 min read

With more people around the world turning to vegetarian and vegan diets, it’s important to understand both the health risks and benefits of following these diets (12).

Abstaining from meat and dairy is a cause for concern because people may not be replacing vitamins and minerals that animal products provide.

Modern society have embraced animals as our primary source of vitamin D, vitamin B12, omega-3 essential fatty acids, protein and bioavailable iron.

Research suggests vegans and vegetarians are at an increased risk for these deficiencies (1). Let’s take a look at each of these in detail to see if there’s a real risk and more importantly, solutions:


Vitamin D

Vitamin D is important for immune function, muscle contractions, and bone health. Vitamin D is primarily found in fish oil with smaller amounts in egg yolk, beef liver and cheese (3). We also synthesise vitamin D from sun exposure, but this depends on the amount of skin exposed, the time of day, where you are living and skin tone. For example, it only takes 15 minutes of sun exposure for very fair to medium fair skin tones to get their recommended daily dose of vitamin D, whereas medium to dark skin tones may need up to 2 hours of sun exposure (14).

Many of us cannot achieve this daily recommendation from the sun alone and must consume dietary sources of vitamin D or supplements (2). Vegans are at a greater risk for deficiency and should try to consume mushrooms treated with ultraviolet light and fortified juice, almond, and rice milk (15). Vitamin D supplements come in D2 or D3 forms. D3 supplements are off limits for vegans because they are made from fish oil or from lanolin, which is made from sheep’s wool. D2 supplements are made from yeast or plants, and is the form found in most vegan and vegetarian supplements. However, research suggests D3 supplements may be more efficacious than D2 for increasing vitamin D levels (17). Luckily, scientists found a way to make a vitamin D3 supplement from a plant source called lichen, which is now available for purchase (16).


Vitamin B12

Vitamin B12 is necessary for protein metabolism, red blood cell formation and nervous system function (5). Deficiencies have been linked to anemia, fatigue and cognitive difficulties (6). Major sources of vitamin B12 include meat, poultry, eggs, milk and shellfish. Very few plant foods, with the exception of nori (seaweed), contain substantial amounts of vitamin B12 (4, 18). Since vegans don’t consume dairy products, B12 deficiency is more common than in vegetarians, although vegetarians are still at a high risk (1, 7). Both dieters can get adequate amounts of B12 from fortified grains, fortified dairy and meat substitutes and vitamin B12 supplements.


Omega-3 Fatty Acids

Omega-3 fatty acids are important in cognitive and behavioral health and may reduce inflammation and protect against chronic disease, like heart disease. Omega-3 deficiency can result in heart problems, dry skin, poor circulation, poor memory and fatigue. Omega-3s are predominantly found in fish and marine oils, such as cod, salmon and krill (8). While these sources provide the recognized useful forms of omega-3, EPA and DHA, omega-3s are also found in flaxseed, soy, walnuts, and pumpkin seeds, but these are ALAs. ALA is converted into the active forms EPA and DHA in the liver, however research found this conversion to be insufficient, as little as 15%, and that conversion is 2.5 times lower in men than women (19). Vegans and vegetarians can improve omega-3 intake by taking omega-3 DHA supplements made from algae or flaxseed oil (16).



Calcium plays a role in blood clotting, bone health, muscle contractions and nerve cell signals. Dairy products are the best source of calcium, but other foods include almonds, leafy greens, broccoli and seafood (13). Research shows that calcium intake between vegetarians and non-vegetarians is very similar, however vegans are at a higher risk of calcium deficiency since they avoid dairy (1). Vegans were actually found to have a 30% higher risk of fracturing a bone due to their decreased intake (1). Vegans should focus on consuming fortified foods with calcium or consider taking a calcium supplement to meet their needs.


Bioavailability of Iron

Dietary iron comes in two forms: heme-iron and non-heme iron. Heme-iron is iron attached to a hemoglobin molecule and found in meat, poultry and fish. Non-heme iron is found in plant based foods like wheat, rice, oats, fruits and vegetables. Heme-iron is more bioavailable, meaning it is better absorbed by body, compared to non-heme iron, with about 20 – 25% of heme-iron absorbed compared to 3 – 10% of non-heme iron (11). The main reason for differences in absorptive capacity is because heme-iron is absorbed intact and less influenced by inhibitory factors. Thus, the lower bioavailability of plant iron is the reason why vegetarians and vegans are at an increased risk for iron deficiency (1, 20).

Phytates found in grains and legumes, and polyphenolics in tea, coffee, spices and some fruit, inhibit iron absorption by up to 40% (11,20). Calcium and zinc can also decrease absorption (1). To optimize iron absorption, vegetarians and vegans should try avoiding these inhibitory factors when eating iron containing plant foods and instead eat them with factors known to increase iron absorption: citric acid, ascorbic acid, lactic acid and beta-carotene (11, 20). Vegetarians and vegans can also try soaking grains, beans and seeds as well as leavening bread to help reduce phytate levels and thereby enhancing iron absorption (1).


Increase Iron Absorption

Decrease Iron Absorption

●       Citric acid: citrus fruit (lemons, limes, oranges)

●       Ascorbic acid: citrus fruit, strawberries, mango, broccoli, green peppers, spinach

●       Lactic acid: cottage cheese, yogurt, kefir, sour milk fructose

●       Beta-carotene: carrots, winter squash, sweet potatoes, cantaloupe, tomatoes, broccoli (11,20)

Polyphenolic compounds:

●    Chlorogenic acid: found in coffee, some herbs, cocoa.

●    Phenolic acid: found in peppermint, some herbal teas, apples

●    Tannins: coffee, cocoa, black tea, walnuts, spices, raspberries, blueberries, apples (11, 20).



Similar to a chain link, proteins are made up of amino acids linked together. Proteins can be a short chain, like 2 amino acids long, or a long chain up to 50 amino acids long. Proteins start to breakdown in the stomach and are completely digested in the small intestine. Amino acids enter the bloodstream and travel to the liver. The liver uses some amino acids to make new proteins and the remaining amino acids leave the liver and are stored in amino acid pool found in cells and the blood. Approximately 55% are deaminated in the liver and fed into metabolic pathways like the Krebs cycle, 25% goes into peripheral tissue, and 20% are used directly by the liver to make proteins (e.g., albumin, lipoproteins) (20). Amino acids have many functions in our body including making structural components like hair and nails, signaling proteins, or enzymes. Proteins are also used as a source of energy, but only during starvation: the body will use carbohydrates and fats first for energy and spare protein to conserve muscle (21).


FACTS: Amino acids are classified into three groups: essential amino acids, nonessential amino acids and conditional amino acids. Essential amino acids cannot be made by the body and can only be obtained through food.


There are nine essential amino acids: methionine, threonine, tryptophan, valine, histadine, isoleucine, leucine, lysine and phenylalanine.


Nonessential amino acids can be made by the body and they include: aspartic acid, alanine, asparagine and glutamic acid. Conditional amino acids only become essential during times of bodily stress or illness when micronutrients are used at a higher rate. These include: arginine, cysteine, glutamine, glycine, proline, tyrosine and ornithine (10).


Not all protein sources are equivalent in protein quality. Protein quality depends on the amount of essential amino acids contained within the food relative to our needs. Plant proteins lack one or more amino acids in amounts needed for protein synthesis, and therefore are designated as “lower quality” or “incomplete proteins” (9, 20). It was a common belief that in order for vegetarians and vegans to consume all essential amino acids in one day, plant proteins must be paired and eaten together, for example beans with rice. This concept is referred to as “complementary proteins.” Now research shows that pairing plant proteins is not as important as eating a variety of plant proteins throughout the entire day (1). Therefore, while protein intake seems to be the major concern among these dieters, as long as a variety of plant proteins are consumed throughout the day, adequate protein intake is attainable.




Animal Sources

Plant Sources

Vitamin D

(3, 15)

Immune health, muscle and cardiovascular  function, bone health, brain development

Fish oil (cod liver), seafood (salmon, tuna, sardines), egg yolk, beef liver, chicken liver, cheese, fortified milk

Fortified milk substitutes, fortified juice, mushrooms treated with UV light

Vitamin B12

(4, 18)

Protein metabolism, red blood cell formation, nervous system function, DNA and RNA synthesis

Meat (beef, poultry, lamb, veal), seafood (trout, tuna, clams), eggs, dairy (milk, yogurt, cheese)

Fortified grains, fortified dairy substitutes, nori (seaweed)



Cognitive and behavioral health, normal growth and development, anti-inflammatory

Fish/marine oil (tuna, salmon, krill)

Canola oil, flaxseed, soy products, walnuts, pumpkin seeds, chia seeds



Blood clotting, bone health, muscle contractions, nerve cell signaling

Canned fish, dairy (milk, cheese, yogurt),

Almonds, leafy greens (spinach, collard greens) broccoli, soy products (tofu), beans, calcium fortified dairy substitutes


(11, 24)

Red blood cell production, oxygen transportation, component of enzymes

Meat (beef, poultry, pork, liver), seafood (clams, mussels, oysters, fish)

Grains (fortified cereals, oatmeal, whole-wheat), fruits (raisins, plums, prunes, apricots),

lentils, kidney beans, quinoa, soybeans


(22, 23)

Hair and nails, enzyme formation, cell signaling, DNA/RNA synthesis, nutrient transport

All animal sources (meat, poultry, fish, seafood)

Quinoa, beans, legumes, soy products (tofu), tempe, chickpeas, lentils, peanuts, nut butters




Today, the vast number of high profile vegan athletes and centenarians are testament to the potential upside of a meat-free diet.

Vegetarians and vegans should not worry about missing out on meat because with proper education and meal planning, these diets are nutritionally adequate to meet protein and micronutrient needs (1). Furthermore, some research shows that vegetarian and vegan dieters tend to have lower blood pressure, lower cholesterol and lower low-density lipoproteins. In general, vegetarians and vegans should:

  • Consume a variety of plant-based proteins with every meal and snack
  • Add supplements to their diet
  • Consider working with a nutritionist or dietitian to achieve specific life or performance goals including ways to limit the risk of a disproportionately high carbohydrate intake, especially refined.


  1. American Dietetic Association. (2009). Position of the American Dietetic Association: Vegetarian Diets. Journal of the American Dietetic Association, 109,1266 – 1282.
  2. Hollis, BW. (2005). Circulating 25-Hydroxyvitamin D Levels Indicative of Vitamin D Sufficiency: Implications for Establishing a New Effective Dietary Intake Recommendation for Vitamin D. The Journal of Nutrition, 2,317 - 322.
  3. National Institutes of Health. (2014). Vitamin D. Factsheet for Health Professionals. National Institutes of Health Office of Dietary Supplements.Accessed at https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
  4. (2015). Vitamin B12. U.S. National Library of Medicine. Accessed at https://www.nlm.nih.gov/medlineplus/ency/article/002403.htm
  5. Key, TJ, Appleby, PN, & Rosell, MS. (2006). Health Effects of Vegetarian and Vegan Diets. Proceedings of the Nutrition Society, 65,35 - 41.
  6. Skerrett, PJ. (2016). Vitamin B12 Deficiency Can Be Sneaky, Harmful. Harvard Health Publications.Accessed at http://www.health.harvard.edu/blog/vitamin-b12-deficiency-can-be-sneaky-harmful-201301105780
  7. Pawlak, R, Parrott, SJ, Raj, S., Cullum-Dugan, D., & Lucas, D. (2013). How Prevalent is Vitamin B12 Deficiency Among Vegetarians? Nutrition Reviews,110 - 117.
  8. University of Maryland Medical Center. (2015). Omega-3 fatty acids. Accessed from http://umm.edu/health/medical/altmed/supplement/omega3-fatty-acids
  9. Messina V, Mangels R, & Messina M. (2004). The Dietitian’s Guide to Vegetarian Diets: Issues and Applications. Jones and Bartlett Publishers.
  10. (2015). Amino Acids. U.S. National Library of Medicine. Accessed at https://www.nlm.nih.gov/medlineplus/ency/article/002222.htm
  11. Iron Disorders Institute. (2009). Iron We Consume. Accessed at http://www.irondisorders.org/iron-we-consume/
  12. Key, TJ & Appleby, PN. (2015). The Long-Term Health of Vegetarians and Vegans. Proceedings of the Nutrition Society.
  13. (2013). Calcium in Diet. U.S. National Library of Medicine. Accessed at https://www.nlm.nih.gov/medlineplus/ency/article/002412.htm
  14. Nair, R. & Maseeh, A. (2012). Vitamin D: The “Sunshine” Vitamin. Journal of Pharmacology and Pharmacotherapeutics, 3(2), 118 - 126.
  15. Simon RR, Phillips KM, Horst RL, & Munro IC. (2011). Vitamin D Mushrooms: Comparison of the Composition of Button Mushrooms (Agaricus bisporus) Treated Postharvest with UVB Light or Sunlight. Journal of Agricultural and Food Chemistry, 59(16), 8724 - 8732.
  16. Vitashine by Vegetology. (2016). Vitashine Vegan Vitamin D. Accessed at https://vitashine-d3.com/
  17. Tripkovic L, Lambert H, Hart K, Smith CP, Bucca G, Penson S, Chope G, HyppĂśnen E, Berry J, Vieth R, & Lanham-New S. (2012). Comparison of Vitamin D2 and Vitamin D3 Supplementation in Raising Serum 25-hydroxyvitamin D Status: A Systematic Review and Meta-Analysis. American Journal of Clinical Nutrition, 95(6), 1357 - 1364. is
  18. Watanabe, F, Yabuta, Y, Bito, T, & Teng, F. (2014). Vitamin B12 Containing Plant Food Sources for Vegetarians. Nutrients, 6(5), 1861 - 1873.
  19. Carmichael, D. (2015). Why Fish Oil is Out Evolutionary Companion and How We Became Estranged. Optimoz. Accessed at http://www.optimoz.com.au/blogs/news/96190471-why-fish-oil-is-our-evolutionary-companion-and-how-we-became-estranged
  20. Hollenbeck, CB. (2014). Nutrition and Metabolism: Protein, Carbohydrate and Lipids. Published by San Jose State University.
  21. Lowell, B, & Goodman, M. (1987). Protein Sparing in Skeletal Muscle During Prolonged Starvation: Dependence on Lipid Fuel Availability. Diabetes, 1, 14 - 19.
  22. United States Department of Agriculture. (2016). Protein Foods Gallery. Accessed from https://www.choosemyplate.gov/eathealthy/protein-foods
  23. (2015). Protein in Diet. U.S. National Library of Medicine. Accessed from https://www.nlm.nih.gov/medlineplus/ency/article/002467.htm
  24. National Institutes of Health. (2016). Iron Dietary Supplement Fact Sheet. National Institutes of Health Office of Dietary Supplements.Accessed at https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/
  25. http://www.telegraph.co.uk/news/science/science-news/12206669/Long-term-vegetarian-diet-changes-human-DNA-raising-risk-of-cancer-and-heart-disease.html


Guest Author
Guest Author

This article was contributed by a guest author with expert knowledge in their field.

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