Why Humans are Not Vegetarians – The Omnivorous Truth



Veganism has come up a lot in my life recently, from meeting vegans, to hearing it on TV, and finding out some of my favourite recording artists are vegan/vegetarians.  Considering I don’t want to be the guy to give unsolicited advice to people I don’t know or to new acquaintances, I took it all as a sign I should write a post about it.


Disclaimer: Vegetarians, Vegans and What this Article will NOT Discuss

Before I even begin, I need to make a couple of things very clear:

  • I fully understand why someone would want to choose an animal free diet for animal welfare reasons, particularly in light of conventional animal farming practices.
    • However, after reading this post, you may want to consider finding an organic farm that has 100% free range (pasture raised) animals or taking up hunting.
  • I fully understand any religious reasons for eating an animal free diet.
  • I fully understand why someone would choose an animal free diet for sustainability reasons given the negative impact of conventional animal farming on the environment; however, consider the following:
  • This post is not meant as judgement for anyone’s current choice of diet. As with all of my posts I am simply providing information with the best of intentions.  In fact, I am 100% certain that with someone following any type of WHOLE FOOD diet (vegan, vegetarian, paleo ketogentic, etc.)  we would agree on more things than we would disagree on.
  • Finally, I am not arguing that it is impossible to be healthy while following a vegetarian or vegan diet; it is simply more difficult as one must use smart supplementation and carefully choose foods to reduce possible nutrient deficiencies and not over consume gut irritating foods (mainly grains).

That being said, let’s get to the main topic of this post, the reasons supporting the fact that humans are built/evolved to eat meat as part of an omnivorous diet, and eating omnivorously is essential for natural optimal health (meaning no modern supplements).

Vegetarians, Vegans and Nutrient Deficiency

Vitamin B12

Honestly, this may be the only argument needed to prove the point that humans are built to eat meat.  B12 is an essential vitamin for humans, meaning we cannot manufacture it in our own bodies so we must obtain it through our diet.  Although the bacteria in our gut does manufacture B12 we are not able to absorb it as the synthesis occurs in the colon, past the point in our intestines where we can absorb B12 (1).  B12 is essential for carbohydrate, fat and protein metabolism, the formation and regeneration of red blood cells, the maintenance of the central nervous system (ex, your brain) and DNA synthesis (2, 3).  B12 deficiency can cause a number of symptoms/conditions including: anemia, neuropathy, degeneration of the spinal cord, incontinence, erectile dysfunction, Alzheimer’s disease, depression, mania, psychosis, fatigue, poor memory, etc (3, 4, 5).  There are a few different forms of B12 that are bioactive in our body, or can be turned bioactive by our body (cyanocobalamin, methlycobalamin, adenosylcobolamin); however, there is also a pseudovitamin B12 which is not bioactive in humans, nor can it be converted by our bodies.

It is well documented that the only food source of B12 is animal products (1), and while some vegans and vegetarians say that certain algae and yeasts naturally contain B12, this is not fully correct.  The B12 contained in any plant source such as algea is the pseudovitamin B12 version, meaning it is not bioactive in humans and therefore not a true source of B12 (6, 7).  Furthermore, yeasts, like nutritional yeast, do not naturally contain B12, this is artificially added by the manufacturers.  This fact is supported by consistent findings that true vegetarians and vegans suffer from suboptimal B12 levels unless they take a B12 supplement (8, 9).  Supplements are all fine and dandy (debatable?), but B12 supplements are not natural and were not around until very recently in human history.  This means that for almost all of human history, we would have had to meet our B12 needs by eating animals.

However, there is a possible alternative…although you may not like it!  Certain insects do contain B12 in its active form; however, this is not the case for all edible insects (10, 11, 12) as nutrient content varies significantly from one species to another.

Bioactive Omega 3 (EPA & DHA)       

Just like B12, there is almost no true plant source of the Omega 3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (13, 14, 15).  Omega 3 fatty acids are also considered essential nutrients and are vital for proper fetal development, including neuronal, retinal, and immune function; positively impact cardiovascular factors such as inflammation, peripheral artery disease, major coronary events, and anticoagulation; as well as positively impact weight management, metabolic function, cognitive function, systemic inflammation, and reduce cancer risk (13).  While there is a plant based version of Omega 3, called alpha linoleic acid (ALA), commonly found in flax, chia and hemp seeds, it is not the active form of Omega 3 (EPA and DHA are) and our body is not efficient at converting ALA to EPA/DHA: conversion is estimated at 5-10% at best (16, 17).  Poor ALA conversion is supported by evidence that vegetarians and vegans have up to 50% lower EPA and DHA levels compared to omnivores (18, 19).

However, there is a vegetarian alternative for those who continue to choose a vegetarian diet: seaweed and algae (14, 15).  These foods can be found as whole foods or in supplement form and should be taken as advised on the bottle, and your health care provider, if you choose to follow a vegetarian or vegan diet.

Retinol (Preformed Vitamin A)

Vitamin A is essential for healthy immune function, fertility, eyesight and skin.  Although there is limited literature about vitamin A deficiency in vegetarians and vegans, there is some evidence that deficiency does occur more often.  Based on our knowledge of vitamin A this makes sense.  It is commonly known that vegetables contain beta-carotene, a form of vitamin A; however, bet-carotene is not the active form of vitamin A (retinol), it is simply a precursor to retinol (20, 21, 22).  Retinol is only found in animal food products such as liver, dairy, and eggs yolks.  It is very important to note that only truly pasture raised and grass-fed animals (if they are ruminants) contain significant amounts of retinol.  Unfortunately, just like with Omega 3, the evidence indicates our ability to convert beta-carotene to retinol is not sufficient (20, 21, 22).  Some estimates indicate that beta-carotene intake is only 16-23% as effective as retinol intake for increasing body levels of retinol (20, 21, 22).  This is supported by findings that beta-carotene supplementation and high beta-carotene intake (vitamin A from vegetables) increases serum beta-carotene levels but does not significantly impact retinol levels (20, 21, 22).

The relationship between retinol and beta-carotene isn’t as black and white as some of the above nutrients as other factors such as parasitic infection and already low retinol levels have a negative impact of beta-carotene to retinol conversion (22); however, the fact remains that vegetarians and vegans are likely to have a higher risk of retinol deficiency.

Vitamin D

Vitamin D regulates calcium metabolism and immune function, reduces inflammation and protects against some forms of cancer.  Vitamin D deficiency has been linked to wide variety of diseases including type I diabetes, multiple sclerosis, rheumatoid arthritis, colorectal cancer, heart disease, and infectious diseases, just to name a few (23).  Sufficient amounts of this vitamin can be obtained from appropriate amounts of sun exposure; however, in northern climates and wintertime, as well as with sunscreen use, sun/UV light exposure is not sufficient to meet our vitamin D needs (24).  Therefore, much of the time, dietary sources of vitamin D are necessary and exclusively come from animal food sources (unless the food is fortified), mainly seafood, eggs, organ meats, and dairy.

Vitamin K2

In the past few years, vitamin K2 has been getting a great deal of attention in the scientific literature and has been deemed essential for calcium metabolism (25).  This means that it is absolutely necessary for bone health, as well as to ensure calcium does not get directed inappropriately to our arteries, causing arterial calcification and an increased risk of cardiovascular disease (25).  While there are many plant sources of vitamin K1, it has different biological roles than vitamin K2 and does not appear to be converted to vitamin K2 (25).  For instance, evidence shows that appropriate vitamin K2 intake reduces the risk of cardiovascular disease and osteoporosis but this is not seen with adequate intake of vitamin K1 (25).  Reliable food sources of vitamin K2 mainly come from animal products such as grass-fed cheese, butter,  and fermented dairy products; pastured egg yolks; liver; and animal meat (to a lesser extent).  Bacteria are the main producers of vitamin K2, meaning that fermented vegetables may also contain this vitamin; however, depending on the bacteria used for fermentation, vitamin K2 content may not reliable.  Natto (fermented soy) and home fermented vegetables such as sauerkraut are the best plant based sources of this vitamin.


There are very few plant sources of complete protein (contains all essential amino acids) in comparison to animal foods.  That being said, by combining grains and legumes in an animal free diet, all essential amino acids can be obtained.  There are also some plant based complete proteins such as quinoa and buckwheat; however, for comparison, beef has 8.5 times the amount of protein as quinoa.  Another factor to consider is the bioavailability of plant based protein.  Compared to animal based food, plant foods contain several ant-nutrients such as phytates, tannins, trypsin inhibitors, etc. that interfere with protein absorption (26, 27, 28).  This means that when eating plant protein, you will not absorb all of the protein that you actual eat.  Given the fact that plants contain much less protein than animal products and plant proteins are less bioavailable, the risk of protein deficiency is higher in vegetarians, particularly vegans (26, 28).  In adults, this risk does not seem to be related to overt diseases; however, adequate protein is very important for proper growth of infants and children and evidence indicates that vegan children do not grow as well as their omnivorous peers (26).   Sufficient protein is also very important for proper structural body health, metabolic health, hormonal health and sexual health.  Finally, we know that our ancestors (ex. hunter gatherers) were very active, as we should be.  Studies done on modern hunter gatherers indicate that their fitness level is what you would expect of developed world humans who participate in a lifetime of physical training at moderate to hard levels, basically athletes (29).  We also know that dietary protein requirements are greater for both strength and endurance athletes and animal protein is shown to be better for building muscle than plant based protein is (30, 31).  While complete protein can be obtained from an animal free diet, the evidence seems to support protein from animal sources is superior and arguably necessary for humans., particularly when we are as physically active as we should be.

Other Possible Nutrient Deficiencies

Compared to omnivores, vegetarians and vegans are at higher risk of iron, calcium and zinc deficiency.  While calcium, iron and zinc intake in vegetarians is similar to that of omnivores, the issue again comes down to bioavailability.  As with protein absorption, the anti-nutrients in plant foods (oxalate, phytate, etc.) reduce the absorption of these nutrients by 50%-85% (17, 32, 33, 34, 35, 36).

Um, but everyone knows vegetarians are healthier and live longer!

Evidence for this belief comes from observational/epidemiological studies where groups of people complete surveys over defined periods of time asking questions about their diet and lifestyle preferences and overall health.  While such studies do their best to adjust the results for other factors impacting health, these studies simply fall victim to the “Healthy User Bias”.  Basically, because being a vegetarian is considered healthy, people who eat vegetarian and vegan diets also do many other healthy things such as limit refined/processed food, exercise, don’t smoke, drink less alcohol, etc. than those that eat meat, simply because meat eating is “considered” unhealthy.  Because the average vegetarian lives a healthier lifestyle than the average meat eater, comparing the 2 does not add value to the debate.  In fact, recent high quality studies show that in the presence of a whole food diet and healthy lifestyle, eating meat is not related to negative health outcomes, and in fact may be good for our health (37).  Interestingly, to control for the healthy user bias, one study compared mortality in a group of vegetarians and omnivores who shopped at health food stores (38).  Their findings revealed no difference in mortality between vegetarians and healthy omnivores.

Take Away

The above are just the main points supporting that humans evolved (or were built/created, depending on your human origins beliefs) as omnivores, not vegetarians.  So, if you are currently vegetarian or considering eliminating animal foods for health reasons, this may not be your best bet.  However, if you choose a vegetarian lifestyle for other reasons, be sure to use smart supplementation and well planned nutrition to reduce your risk of common nutrient deficiencies.


The Barefoot Golfer

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