This is an update of an article I published in 2011. I affirm that animal products are among the most nutrient-dense foods you can eat and that vegetarians and vegans are at risk for multiple nutrient deficiencies. I have included up-to-date research and expanded the list of nutrients that are often lacking in vegetarian and vegan diets.
Maybe you have considered going vegetarian or vegan for the health benefits. Or maybe you know someone who feels strongly about it as an ethical choice, and you wonder if they can really follow the diet in a healthy way. I respect these reasons and appreciate anyone who thinks deeply about the social and spiritual impact of their food choices—even if my own exploration of these questions has led me to a different answer.
But many choose a vegetarian diet because they’re under the impression that it’s a healthier choice from a nutritional perspective. It is this last reason that I’d like to address in this article. For the last 50-plus years, we’ve been told that meat, eggs, and animal fats are bad for us and that we’ll live longer and enjoy superior health if we minimize or avoid them. This idea has been so thoroughly drilled into our heads that few people even question it anymore. In fact, if you asked the average person on the street whether a vegetarian or vegan diet is healthier than an omnivorous diet, they’d probably say yes. But is this really true?
If You Want Nutrient-Dense Foods, You Need to Eat Animal Products
Plant-based diets emphasize vegetables, which are quite nutrient dense, and fruits, which are somewhat nutrient dense. They also typically include large amounts of cereal grains (refined and unrefined) and legumes, both of which are low in bioavailable nutrients and high in anti-nutrients like phytate. Most importantly, vegetarian and vegan diets eschew organ meats, other meats, and fish and shellfish, which are among the most nutrient-dense foods you can eat. (1)
Followers of vegetarian and vegan diets, beware: You could be missing out on B12, iron, calcium, and other key nutrients. Is it time to rethink your diet plan and add meat back to your plate? Find out.
Vegan diets, in particular, are almost completely devoid of certain nutrients that are crucial for physiological function. Deficiencies can take months or years to develop, and many are easily missed because they are not routinely tested for in primary care settings. Several studies have shown that both vegetarians and vegans are prone to deficiencies in:
- Vitamin B12
- Long-chain fatty acids EPA and DHA
- Fat-soluble vitamins like A and D
Let’s take a closer look at each of these nutrients.
Vegetarian and Vegan Diets Don’t Provide Enough Vitamin B12
B12 deficiency is especially common in vegetarians and vegans. To properly evaluate B12 status, total serum vitamin B12 isn’t enough. A better marker for vitamin B12 is holotranscobalamin II, the biologically active fragment, which should be measured along with total homocysteine and methylmalonic acid, both of which are usually decreased in later stages of vitamin B12 deficiency. (2) The most recent studies using more sensitive techniques for detecting B12 deficiency have found that up to 77 percent of vegetarians and 92 percent of vegans are B12 deficient, compared to just 11 percent of omnivores. (3, 4, 5)
Vitamin B12 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. B12 deficiency can cause numerous symptoms, including:
- Memory loss
- Neurological and psychiatric problems
- And much more …
It’s a common myth among vegetarians and vegans that it’s possible to get B12 from plant sources like:
- Fermented soy
- Brewer’s yeast
These plant foods don’t contain B12. They contain B12 analogs, called cobamides, that block the intake of—and increase the need for—true B12. (6)
If You’re Vegan, You Might Be Missing out on Calcium
You know that calcium is important for bone health, but did you know it’s essential for muscle and nerve function and that it’s involved in blood clotting? On paper, calcium intake is similar in vegetarians and omnivores (probably because both eat dairy products). Vegans, however, are often deficient. (7, 8, 9)
Calcium bioavailability from plant foods is affected by their 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. (10) So while leafy greens like spinach and kale have a relatively high calcium content, the calcium is not efficiently absorbed during digestion.
One study suggests that it would take 16 servings of spinach to get the same amount of absorbable calcium as an eight-ounce glass of milk. (11) That would be 33 cups of baby spinach or around five or six cups of cooked spinach. There are a few vegetables listed in this paper that have higher levels of bioavailable calcium, but it’s important to note that all of the vegetables tested required multiple servings to achieve the same amount of usable calcium as one single serving of milk, cheese, or yogurt.
This suggests that trying to meet your daily calcium needs from plant foods alone might not be a great strategy. For those who don’t tolerate dairy well, fish with edible bones like sardines are great sources of calcium on a Paleo diet.
You’re Also More Likely to Be Iron-Deficient on a Plant-Based Diet
Vegetarians and omnivores often have similar levels of serum iron, but levels of ferritin—the long-term storage form of iron—are lower in vegetarians than in omnivores. (12, 13) This is significant, because ferritin depletion is the first stage of iron deficiency.
For example, this study of 75 vegan women in Germany found that 40 percent of them were iron deficient, despite average iron intakes that were above the recommended daily allowance. (14) Among Australian men, iron intake among vegetarians and vegans was 29 to 49 percent higher than omnivores, but their serum ferritin concentrations were barely half that of omnivores. (15) Despite similar iron intakes, another study published this year showed vegans and female vegetarians having low ferritin levels. (16)
Why would this be? As with calcium, the bioavailability of the iron in plant foods (nonheme iron) is much lower than in animal foods (heme iron). Plant-based forms of iron are also inhibited by other commonly consumed substances, such as:
Red Meat, Fish, and Poultry Are Your Best Sources for Zinc
Zinc is important for the immune system, cell growth, and wound healing. You won’t usually see overt zinc deficiency in Western vegetarians, but their intake often falls below recommendations, probably because red meat, poultry, and fish are the best sources.
This is another case where bioavailability is important; many plant foods that contain zinc also contain phytate, which inhibits zinc absorption. Vegetarian diets tend to reduce zinc absorption by about 35 percent compared with an omnivorous diet. (19) Thus, even when the diet meets or exceeds the RDA for zinc, deficiency may still occur. (20) One study suggested that vegetarians may require up to 50 percent more zinc than omnivores for this reason. (21) A meta-analysis of 34 studies found that both zinc intakes and serum zinc concentrations were lower in vegetarians than non-vegetarians. (22)
You Might Be Missing out on the Benefits of Essential Fatty Acids
Plant foods do contain linoleic acid (omega-6) and alpha-linolenic acid (ALA, omega-3), both of which are considered essential fatty acids. In this context, an essential fatty acid is one that can’t be synthesized by the body and must be obtained in the diet. However, an increasing body of research has highlighted the benefits of the long-chain omega-3 fatty acids EPA and DHA. These fatty acids play a protective and therapeutic role in a wide range of diseases: (23, 24)
- Alzheimer’s disease
- Cardiovascular disease
- Autoimmune diseases like rheumatoid arthritis
While it is possible for some ALA from plant foods to be converted into EPA and DHA, that conversion is poor in humans: between 5 and 10 percent for EPA and 2 and 5 percent for DHA. (25)
Although no official recommendation exists, the daily suggested intake of combined DHA and EPA is around 250 to 500 mg. In theory, this means vegans and vegetarians would need to consume between five and 12.5 grams of ALA per day to obtain 250 mg of DHA. In reality, vegetarians and vegans consume merely 0.97 g/day and 0.86 g/day of ALA, respectively, according to a study of over 14,000 Americans. (26)
Vegetarians have 30 percent lower levels of EPA and DHA than omnivores, while vegans have 50 percent lower EPA and nearly 60 percent lower DHA. (27, 28) Moreover, the conversion of ALA to DHA depends on zinc, iron, selenium, and pyridoxine—nutrients that vegetarians and vegans are less likely than omnivores to get enough of. (29, 30, 31, 32) Eating 12 to 16 ounces of cold-water fatty fish per week remains the best way to get adequate EPA and DHA. The fish will also provide bioavailable protein and selenium.
Vitamins A and D: What You’re Missing
Fat-soluble vitamins play numerous and critical roles in human health. Vitamin A promotes healthy immune function, fertility, eyesight, and skin. Vitamin D regulates calcium metabolism, regulates immune function, reduces inflammation, and protects against some forms of cancer.
These important fat-soluble vitamins are concentrated, and in some cases found almost exclusively, in animal foods like:
- Organ meats
- Dairy products
Some obscure species of mushrooms can provide large amounts of vitamin D, but these mushrooms are rarely consumed and often difficult to obtain. This explains why vitamin D levels are often low in vegetarians and even lower in vegans. (33, 34, 35, 36)
The idea that plant foods contain vitamin A is a common 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. (37, 38) For example, a single serving of liver per week would meet the RDA of 3,000 IU. 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.
Moreover, traditional cultures consumed up to 10 times the current RDA for vitamin A. It would be nearly impossible to get this amount of vitamin A from plant foods without juicing or taking supplements. And if supplements aren’t consumed with a fatty meal, the actual absorption will be low. (39)
Vegans and Vegetarians, You Could Be Missing These Key Nutrients
If you don’t eat meat or other animal products, you could also be missing out on:
Vegetarian and vegan diets, along with the Standard American Diet, pose risks of choline deficiency. (40) Choline is required for:
- Healthy cell membrane function
- Cognitive development in children
It’s so important that the FDA recently set a daily recommended intake of 550 mg for men and 425 mg for women, which should increase to 450 mg during pregnancy and 550 mg during breastfeeding. Recent research suggests that only 8.5 percent of women meet the daily choline requirement. (41) With egg yolks and organ meats as the most potent sources of choline, it’s not surprising that even omnivores are not getting enough. This is another reason I encourage giving organ meat dishes another try.
Creatine plasma and muscle levels are usually lower in vegetarians than in omnivores, as meat provides the richest source of creatine. (42) Creatine may play an important role in cognitive function. A randomized controlled trial found that six weeks of oral creatine supplementation significantly improved vegetarians’ performance on tests of fluid intelligence and working memory. The difference in scores between groups was enormous. (43)
Another study found that creatine supplementation in vegetarians improved memory, while having no effect on fluid intelligence or working memory in meat-eaters. (44) These results suggest that vegetarians’ baseline scores may have been impaired due to low creatine intake.
Taurine has a central role as a neurotransmitter, promotes the development of the central nervous system, and upholds the structure of cell membranes. Although the body can synthesize small amounts of taurine, vegetarians and vegans often still have low plasma and urinary taurine levels because taurine is found primarily in animal products. (45, 46) Low plasma taurine in newborns is associated with lower scores on mental development and arithmetic tests at age seven, suggesting that dietary taurine aids in neural development. (47)
Methionine is another amino acid that is restricted on a plant-based diet. Low methionine intake has been linked to longevity in scientific research. However, methionine is still an essential amino acid, and too little methionine may impair detoxification and reduce fertility. (48, 49) After being activated using ATP, methionine becomes the universal methyl donor.
On the flip side, too much methionine can also pose problems. After methyl donation, methionine becomes homocysteine and must be recycled back to methionine by B12, folate, or betaine (derived from choline). Because meat is high in methionine, diets heavy in muscle meats but low in connective tissues can result in increased homocysteine levels, a risk factor for CVD.
That said, studies have shown that vegetarians and vegans have significantly higher homocysteine levels on average than omnivores. (50) In one study, the average homocysteine level among vegetarians was 13.9 nmol/L and among vegans, 16.4 nmol/L, compared to 11.3 nmol/L for omnivores. (51) This puts most vegetarians and vegans in a range that carries significant risk of CVD. In fact, according to one study:
The prevalence of hyperhomocysteinemia among vegetarians may actually be higher than that among non-vegetarians already diagnosed with heart disease. (52)
Vegetarians and vegans don’t consume as much glycine as meat-eaters, as the richest sources are the “odd bits” of animal foods, like: (53)
Glycine is one of the building blocks of collagen, found in our connective tissues. In addition to its structural role, glycine can also act as a neurotransmitter, plays a role in blood sugar regulation, and stimulates the production of glutathione, the body’s master antioxidant. (54, 55, 56, 57)
Some Paleo dieters can be susceptible to low glycine intake, too, if they are eating tons of muscle meat and ignoring the “nose-to-tail” philosophy. Glycine helps balance out methionine levels, in part by acting as a buffer for excess methyl groups. Low choline and glycine intake, common in vegetarians and vegans, can further contribute to high homocysteine levels and increased risk of CVD. Eating bone broth regularly can help balance glycine/methionine levels.
While a few studies show no difference in selenium status among diet types, most research shows lower intake and/or levels in vegetarians and vegans compared to omnivores, including one study that measured glutathione peroxidase, a selenium-dependent enzyme and an excellent marker of active selenium status. (58, 59, 60, 61) Selenium has a role in immune function, supports thyroid hormone synthesis, and protects the thyroid from excess iodine damage. (62, 63) Selenium also helps prevent mercury toxicity. (64)
- Brazil nuts
- Crimini mushrooms
- Some sea foods
I recommend getting selenium from whole foods instead of supplementing, as selenium supplementation can be dangerous.
Eating Animal Products Could Also Help Your Thyroid Health
Thyroid hormone synthesis requires iodine, a nutrient that can be lacking from omnivore and plant-based diets alike. Most iodine comes from the sea; the soil—and therefore vegetables grown in soil—usually contains very little. In a typical mixed diet, the highest sources of iodine are iodized salt and animal products like:
- Dairy products
Vegetarians and vegans are at risk for low iodine intake. (67)
In the Boston area, urinary iodine levels in vegans were barely half that of vegetarians, and vegans were at high risk of iodine deficiency. (68) Several studies of Scandinavian populations confirm that vegans finished last in iodine intake and/or urinary iodine levels. (69, 70, 71) To make matters worse, isoflavones found in soy products, which are sometimes consumed in large quantities in vegan and vegetarian diets, may exacerbate iodine deficiency and hypothyroidism. (72)
But even those following a Paleo template can be at risk for iodine deficiency if they are not regularly consuming seafood. (73) Sea vegetables, especially kelp, are the highest sources of iodine ounce for ounce.
Your Kids Need Nutrient-Dense Foods to Thrive
Because of the prevailing idea in our culture that vegetarian and vegan diets are healthy, more and more children are being raised from birth (and even from conception!) on meat-free diets. Both the Academy of Nutrition and Dietetics (AND) and USDA have said that vegetarian and vegan diets are safe during pregnancy, but critical analyses by several researchers have questioned whether these recommendations are based on sufficient evidence. One review remarked that “the evidence on vegan–vegetarian diets in pregnancy is heterogeneous and scant,” suggesting that more research is needed to answer the question of whether they are, in fact, safe during pregnancy. (74)
Studies have shown that kids raised until age six on a vegan diet are still B12 deficient years after adding at least some animal products to their diet. One study found an association between B12 status and measures of intelligence and memory, with formerly vegan kids scoring lower than omnivorous kids. (78) Devastating case studies have reported B12 deficiency in young vegan children that have led to neurological damage and developmental delays. (79, 80)
Low nutrient intake extends beyond vitamin B12. Other case studies have attributed hypothyroidism in young children to a maternal and/or childhood vegan diet. (81, 82) Compared to omnivores, breast milk from vegan mothers had lower levels of DHA and EPA, which are vital for brain development, especially in the first year of life, when a baby’s brain literally doubles in size. (83) In short, just like adults, children on vegetarian and vegan diets often have lower intakes of iron, iodine, vitamin A, zinc, and more.
Your Best Choice for Optimal Nutrition Isn’t a Vegetarian or Vegan Diet, but a Paleo Template
With care and attention, I think it’s possible to meet most of your 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 or bend the rules and take fish oil or cod liver oil as a supplement. (84) Still, while it may be possible to obtain adequate nutrition on a vegetarian diet, it is not optimal—as the research above indicates.
I don’t 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:
- Bioavailable iron and zinc
- Vitamins A and D
- EPA and DHA
It’s worth pointing out that there are genetic differences that affect the conversion of certain nutrient precursors (like beta-carotene and alpha-linolenic acid) into the active forms of those nutrients (like retinol and EPA and DHA, respectively), and these differences may affect how long someone will be able to follow a vegetarian or vegan diet before they develop nutrient deficiencies. This explains why some people seem to do well for years on these diets, while others develop problems very quickly.
Is It Time to Rethink Your Diet?
From an evolutionary perspective, is difficult to justify a diet with low levels of several nutrients critical to human function. While it may be possible to address these shortcomings through targeted supplementation (an issue that is still debated), it makes far more sense to meet your nutritional needs from food.
This is especially important for children, who are still developing and are even more sensitive to suboptimal intake of the nutrients discussed in this article. Like all parents, vegetarians and vegans want the best for their children. Unfortunately, many are not aware of the potential for nutrient deficiencies posed by their dietary choices.
I hope this article can serve as a resource for anyone on a plant-based diet, whether they choose to start eating meat (or animal products, in the case of vegans) again or not.
What are your thoughts? Are you considering changing from a meat-free diet to a Paleo template? Let me know below!