There are many reasons why someone may decide to go vegan or vegetarian. Some are compelled by environmental animal feeding operations while others by ethical or religious reasons. I respect these choices, even if my own exploration of these questions has led me to a different answer.
But many choose vegan or vegetarian diet because they believe it’s a healthier choice from a nutritional perspective. For the last 50 years, we have been told that meat, eggs, and animal fats are bad for us. This is has been so drilled into our brains that very few people ever question it anymore.
Plant-based diets emphasize vegetables, which are very nutrient dense, and fruits, which are somewhat nutrient dense. However, these diets often include larger amounts of cereal grains (refined and unrefined) and legumes, both of which are low in bioavailable nutrients and high in anti-nutrients such as phytate. They also avoid organ meats, meats, fish, and shellfish, which are among the most nutrient-dense foods you can eat (1).
Vegan diets, in particular, are almost completely devoid of certain nutrients that are crucial for physiological function. Several studies have shown that both vegetarians and vegans are prone to deficiencies in B12, calcium, iron, zinc, the long-chain fatty acids EPA and DHA, and fat-soluble vitamins such as A and D.
Let’s take a closer look at these nutrients on a vegan or vegetarian diet:
B12
This vitamin works together with folate in the synthesis of DNA and red blood cells. It’s also involved in the production of the myelin sheath around the nerves, and the conduction of nerve impulses. Studies have shown that 68% of vegetarians and 83% of vegans are deficient, compared to 5% of omnivores (2). B12 deficiencies can cause symptoms of fatigue, lethargy, weakness, memory loss, neurological and psychiatric problems, anemia, and much more! It’s also a myth that it’s possible to get B12 from plant sources such as seaweed, fermented soy, spirulina, and brewers yeast, but these foods actually contain B12 analogs called cobamides that block the intake of and increase the need for B12.
Calcium
The bioavailability of calcium from plant foods is affected by vegans levels of oxalate and phytate, which are inhibitors of calcium absorption and thus decrease the amount of calcium the body can extract from plant foods (3). So while leafy greens like spinach and kale have a relatively high calcium content, the calcium is not efficiently absorbed during digestion.
Iron
Ferritin, the long-term storage form of iron are notably lower in vegetarian and vegans (4). As with calcium, the bioavailability of the iron in plant foods is much lower than in animal foods. Plant-based forms of iron are also inhibited by other commonly consumed substances, such as coffee, tea, dairy products, supplemental fiber, and supplemental calcium. This explains why vegetarian diets have been shown to reduce non-heme iron absorption by 70% and total iron absorption of 85% (5).
Zinc
Although deficiencies not often seen in Western vegetarians, their intake still often falls below recommendations. This is another case where bioavailability is important. Many plant foods containing zinc also contain phytate, which inhibits zinc absorption by about 35% compared to omnivorous diets (8). Therefore, deficiency may still occur. This study suggested that vegetarians may even require 50% more zinc than omnivores (9).
EPA and DHA
Plant foods contain both linoleic acid (omega-6) and alpha-linolenic acid (omega-3) which are both considered to be essential fatty acids, meaning that they cannot be synthesized or produced by the body and therefore must be obtained through food. Of the two essential amino acids, EPA and DHA from omega-3 fatty acids play a protective role in the body such as fighting disease, cancer, asthma, depression, cardiovascular disease, ADHD, and autoimmune disease by greatly reducing inflammation in the body. Although it is possible for some omega-3 fatty acids from plant foods to be converted to EPA and DHA, that conversion is poor: between 5-10% for EPA and 2-5% for DHA (10). Vegetarians also have 30% lower EPA and nearly 60% lower DHA (11).
Fat-Soluble Vitamins
Probably one of the biggest problems with vegetarian and vegan diets is their near total lack of the fat-soluble vitamins A and D. Fat-soluble vitamins are critical to human health. Vitamin A promotes healthy immune function, fertility, eyesight, and skin. Vitamin D regulates calcium metabolism, immune function, reduces inflammation and protects against many forms of cancer. These fat-soluble vitamins are concentrated and found almost exclusively in animal foods: seafood, organ meats, eggs and dairy products (12). Also, the idea that plant foods contain vitamin A is a misconception. Plants contain beta-carotene, the precursor to active vitamin A (retinol). While beta-carotene is converted into vitamin A in humans, the conversion is inefficient (13).
With care and attention, it is possible to meet nutrient needs with a VEGETARIAN diet that includes liberal amounts of pasture-raised, full-fat dairy and eggs, with one exception: EPA and DHA. These long-chain omega fats are found exclusively in marine algae and fish and shellfish, so the only way to get them on a vegetarian diet would be to take a microalgae supplement (which contains DHA) or to take fish-oil or cod-liver oil as a supplement (which isn’t vegetarian). Still, while it may be possible to obtain adequate nutrition on a vegetarian diet, it is not optimal—as the research above indicates.
I do not, however, think it’s possible to meet nutrient needs on a vegan diet without supplements—and quite a few of them. Vegan diets are low in B12, bioavailable iron and zinc, choline, vitamin A & D, calcium, and EPA and DHA. So if you’re intent on following a vegan diet, make sure you are supplementing with those nutrients
When working with clients who I believe may suffer from nutrition deficiencies I often run a micronutrients blood test to see exactly where we need to fill in the gaps. Click here more information on testing and nutrition consulting.
Guest post by Rachel Scheer, BS Nutrition & Dietetics from Baylor University. DFW Clinical Nutritionist (www.rachelscheer.com - @rachelscheer)