Does Saying Humans Are Omnivores Justify Eating Animals?

chimp's canines

A chimp’s canines are long and pointed similar to that of other animals which are considered either omnivores or carnivores.

The omnivore “neutrality” defense

A common justification for eating animals is the statement, “Humans are omnivores.” Yet, being biologically omnivorous neither compels us to eat animal products nor erases our moral obligation to minimize the harm that results from our food choices. Aside from the long-standing debate over whether humans are natural herbivores or true omnivores, if, for the sake of argument, we accept the widely-held view that humans are omnivores, this still does not change the fact that we can easily get all of our nutrients from a plant-based diet. And most of us have access to a wide range of delicious plant-based foods. Vitamin B12, the only nutrient vegans need to be vigilant about supplementing, is inexpensive and is also recommended in supplement form for non-vegans, who are equally prone to deficiencies. More on vegans and B12 here.

In discussions, the statement “humans are omnivores” is often used to suggest that eating animals— more specifically, breeding and raising billions of animals for slaughter— is somehow morally neutral. But we can easily see why this betrays our ethics by looking at the following hypothetical scenario. Imagine applying this line of reasoning to some other human behavior we want to justify. For example, using this line of reasoning, a man defends killing his wife on the basis that “humans are natural murderers,” arguing that we have a natural capacity for, and a long history of, murdering. But of course we would never justify such violent acts as murder, rape or torture as morally acceptable simply because these behaviors can be said to come naturally to us. And, yet, all of these violent practices are systematically carried out against other animals to turn them into food products for our enjoyment.

So what does it actually meant to be an omnivore?

The statement “humans are omnivores” is all too often used as a smoke screen to blur the important distinctions between omnivores and carnivores, suggesting that our killing and eating of animals is as natural and necessaery as it is for, say, lions and tigers and other obligate carnivores who eat other animals for reasons of survival. But being an omnivore simply means that we are capable of obtaining nutrients from both plant and animal matter, not that we must eat animals. And yet the popular characterization of omnivorism asserts that a sensible omnivore eats at least some meat, dairy or eggs on a regular basis as part of balanced, everything-in-moderation diet. But in fact being a human omnivore in contemporary times simply means we have the luxury of choosing from plant-based foods and animal-based foods. And since all the nutrients we need can be obtained from plant foods, there is no justification for the pointless violence and suffering that underpin eating animal foods, particularly when we could so easily avoid it.

Our closest primate relatives, chimpanzees, are also considered omnivores. Yet despite the fact that chimpanzees have huge, pointed canine teeth, the flesh of other animals is only a marginal part of their diet. Dale Peterson, who has studied chimps extensively in their natural habitat, explained to us in an interview that chimps, if given the opportunity to satisfy their hunger with exclusively plant-based sources, might very well ponder the morality of eating other animals. But even if they didn’t, the energy expended to kill animals for food is far greater than that used in eating plants, which may partially explain why other animals are but a small part of the chimps’ diet.

Sorting through nutritional myths

Unlike biological carnivores, we will not get sick or die from malnutrition if we stop eating dairy, eggs and flesh products. On the other hand, if we stop eating plant foods, we will likely become malnourished. On both a physical and psychological level, humans can thrive on a plant-based diet. Even many famous athletes perform at their peak on plant-based diets. And replacing animal foods with plant foods does not mean we are going against our biology, which is a popular view today. While statistics on the size of the global vegan population are sparse, there are estimated to be millions of vegans in the U.S. alone, and there is ample evidence of healthy populations of people all over the world who traditionally consume little to no animal products. The leading health authorities in the U.S., U.K., Canada and Australia all confirm that well-planned vegan diets are a safe, healthy and viable option for all age groups.

Still, some insist that a vegan diet isn’t for everyone or that some people fail to thrive on a vegan diet. Ex-vegans are often quick to blame a plant-based diet for a wide range of health problems while ignoring all of the other factors that can contribute to poor health, but correlation is not causation. According to nutrition expert Micaela Karlsen, the trend in thinking that says each person requires a highly personalized nutrition regimen, while good at selling books and diet plans, is completely inaccurate. As Karlsen explains, “Human beings are one species; we are all the same animal, with the same digestive physiology. And, as is true of all species, we do not require personalized nutritional programs unless we are dealing with a specific disease or some other very unusual condition.”

For a concise reference to plant-based nutrition, we recommend Vegan for Life by Jack Norris and Virginia Messina, both registered dieticians. Vegan for Life will answer all of your concerns and questions. It is backed up by the best peer-reviewed scientific research, and includes a chapter on how to evaluate competing nutritional claims in an age of confusing and conflicting information, much of which is directly funded or heavily influenced by the meat, dairy and egg industries.

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About Robert Grillo

Robert Grillo is the director of Free from Harm which he founded in 2009 to expose the food industry’s exploitation of animals and foster greater empathy for farmed animals. As an activist, author and speaker, Grillo focuses awareness on the animal’s experience and point of view, drawing on insights from sociology, psychology, popular culture, ethics and social justice to bridge the gap between humans and other animals. As a marketing communications professional for over 20 years, Grillo has worked on large food industry accounts where he acquired a behind-the-scenes perspective on food branding and marketing. His new book, Farm to Fable: The Fictions of Our Animal Consuming Culture, reveals how popular culture uses a variety of fictions that condition us to consume animal products and perpetuate fasle perceptions of animals that make us feel better about exploiting them


  1. “…there is no credible scientific evidence that the human body needs meat…”. I am vegan, and I didn’t find non animal source of vitamin B12. But the unusual thing about that vitamin is that its the ONLY nutrient that is problematic, so it could be that in perfect natural conditions we would get it from unwashed plants and dirt, but all of that is very weak argument, so we still cant said that every nutrient is in vegan diet. That question is the only one that still gives me trouble in any discussion, I just can tell that I can get B12 in “natural way” from plants.

    • B12 is widely available in many of the fortified plant foods that we eat on a daily basis as well as in vegan supplement form as I am sure you already know. B12 does NOT originate in animal flesh. It is a bacteria that originates in the soil. Thus, as you noted, plants often have it prior to being washed off. The point I am making is that we never need to go through an animal to get our B12. The discussion about whether a vegan diet is “natural” because it may not offer as much B12 is another issue. And it’s one I think is obsolete in the age we live in. The fact is we consume a lot of fortified foods and many people use supplements to support their diet. Some must do so. Even heavy meat eaters can be deficient in B12. For a great discussion on this, see the book Vegan for Life by registered dietitians Norris and Messina.

      • The above article by Robert Gillo ends with a link to a well know article by Milton Mill, MD, which ends with “we must conclude that humankind’s GI tract is designed for a purely plant-food diet.” I submit this is false, as is the statement from Robert Grillo’s article that “The truth is that all the nutrients we need can be obtained from plant foods”. I disagree; even your above reply to tomislav5689 above acknowledges that on a vegan diet, B12 (most easily acquired from meat or seafoods) is acquired by eating fortified plant foods or supplements. Obviously, if humans were designed for a purely plant-food diet, we wouldn’t require supplements or have to fortify our plant foods. It seems to me that like chimps, humans are omnivores, and while we don’t need to consume anything near 50% of our diet as meat, for an adequate amount of B12, we do, like chimps, require 1-5% of our diet as such.

        • Hi Michael,

          Supplements are recommended widely by doctors and the world’s leading nutrition organizations for people on all kinds of diets. To suggest that a vegan diet is somehow unnatural because it is recommended that vegans take a B12 supplement fails to address the fact that many meat-eaters have B12 deficiencies that can only be addressed with supplementation. B12 does not originate in animal flesh. It is a bacterial agent that originates in the soil and the B12 supplements widely in use today are non animal derived.

          In 2009, the American Academy of Nutrition & Dietetics, the U.S.’s oldest, largest and foremost authority on diet and nutrition, also recognized that humans have no inherent biological or nutritional need for animals products: “It is the position of the American Dietetic Association that appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases. Well-planned vegetarian diets are appropriate for individuals during all stages of the life cycle, including pregnancy, lactation, infancy, childhood, and adolescence, and for athletes.”

          While a well-balanced vegan diet can easily provide all of the nutrients we need to thrive, that doesn’t mean that all vegans are healthy. Just as people who eat meat, dairy and eggs often suffer from nutrient deficiencies, a poorly planned or junk-food vegan diet can also fail to meet nutritional needs, leading to health problems. Total raw food diets and diets composed of only very-low-fat foods can also make it harder for some people to get all the necessary nutrients. But with the rare exception of someone who suffers from multiple serious plant-food allergies, science now recognizes that a healthy vegan diet is a safe option for everyone.

          So what about ex-vegans? Although some former vegans will have experienced poor health as a result of an imbalanced diet, many others were simply struggling with difficult cravings. And while cravings— and the discomfort they produce— are real, it’s important to recognize that a craving is not a need. As much as it may feel like we are actually suffering from a life-threatening cheese deficiency, we know that withdrawal from highly pleasurable or addictive sensations can produce a multitude of physiological responses, including feelings of depression, fatigue and deprivation. We also know that cheese cravings aren’t indicative of an actual biological need, because cow’s milk is made for baby cows.

          It’s also true that, just like meat-eaters, some vegans will struggle more than others to stay healthy. As Ginny Messina, R.D., observes: “Nutrient needs vary among individuals, so some people may need to work a little bit harder to obtain everything they need. And some vegans are not getting enough of what they need because they are eating diets that are too restrictive and/or they are not taking appropriate supplements.

          – See more at:

        • I would rather take a B12 supplement than the cocktail of medications most American are on because of their animal-based diets. Is it natural to eat animal products even in allegedly “small” amounts even if it requires one to take diabetes, heart disease and lipid lowering drugs to maintain such a diet? Michael, we can indeed get all the nutrients we need from a plant based diet as 600 million vegetarians and growing are proving. And if we can live healthy lives without harming anyone, why wouldn’t we?

          • I haven’t heard before that most Americans are on a cocktail of medications; even if true, it sounds like as assumption to say it’s because of their animal based diets. I would say it’s “natural” to eat small amounts of animal products. I personally don’t know anyone taking diabetes, heart disease, or lipid lowering drugs, meat eater or vegan; even if I did, there’s a big difference between causation and correlation.


          • “The fact that a behavior is commonly found in nature is ordinarily insufficient to demonstrate the moral rightness of the behavior. To take one example, forced sexual intercourse is very frequently found in nature. (5) What we call “rape” is common among males of various species who are not voluntarily selected by females, perhaps because of the males’ otherwise poor genetic endowments. Through rape, an unwanted male is able to perpetuate his genetic lineage (including perhaps the inclination to engage in forced intercourse). A socio-biologist might interpret the history of rape by conquering human armies in warfare as an example of this phenomenon, through which men from an enemy nation force women who have no interest in coupling with them to extend the genetic reach of the invading enemy. (6)

            Another instance of behavior found frequently in nature is infanticide, the killing of infants. Among a number of species, when a new male animal becomes the leader of a group of pregnant females, for example, it is common for him to kill the babies of the females as soon as they are born. (7) The evolutionary benefit of this behavior is clear. If the females are nursing another male’s genetic offspring, the new male cannot impregnate them. Infanticide in such a case promptly terminates lactation and leads to fertility in the females. This, in turn, allows the male to mate with the females and expand his own genetic lineage.

            A third common behavior among humans and our primate relatives is xenophobia. Literally the fear of foreigners, it describes a reaction of hostility to others within the same species that fall outside one’s own group. (8) When one male chimpanzee encounters another with whom he is unfamiliar, a common reaction is extreme violence. (9) Likewise, racism, international conflicts, and inter-group hatreds have formed a persistent part of the human story. (10)

            Perhaps a relic of a time in our evolutionary history during which strangers would generally pose an immediate threat, tribal loyalties and antipathy to outsiders may have become firmly ingrained in our DNA. (11) We can see disturbing echoes of such insider/outsider status allocation even among relatively young children. (12) This apparently naturally occurring behavior has recently led to school anti-bullying policies in response. (13)

            The three examples, of naturally occurring rape, infanticide, and xenophobia, should help dispel the notion that acting in ways that come “naturally” automatically fulfills our moral obligations. In human societies, we evaluate our own behavior critically and negatively judge many instances of naturally occurring conduct. Indeed, if a particular behavior were sufficiently rare, it would suggest that people lack any drive to engage in it, and we would probably need no moral rules forbidding it. From this perspective, it is precisely because both virtue and vice come “naturally” to us that we must critically consider our activities and choose what to do (and what not to do) on the basis of moral reflection. We cannot, in other words, unreflectively do whatever we feel like doing and then rely on our inclination to act as necessarily vindicating what we have chosen to do.” Sherry Colb

            – See more at:

          • “However much people may enjoy eating animal products, then, nature does not unambiguously commit us to, or reward us with good health for, consuming them. Our nature is quite different from that of lions, and our choices about what we eat are accordingly far more flexible and correspondingly susceptible to moral scrutiny. Where we have another choice—indeed a more healthful choice—for which our anatomy and physiology amply equip us, we cannot simply invoke nature to justify what we do. It is true that we could not reasonably accuse lions of acting immorally in consuming animals. But simply put, we are not lions.” – Read Sherry Sherry F. Colb-Vegan’s excellent chapter from her book at:

        • Michael,

          first off, please see this to read a scientific analysis of why humans are far closer anatomically to herbivores than we are omnivores.

          using your own line of reasoning, one could very easily come to the conclusion that humans are not meant to consume flesh at all because unlike any other species, we require it to be cooked in order that we do not get sick or die.

          B-12 is not animal or plant based but instead is produced by bacteria. humans used to get sufficient B-12 from the soil on the plant foods they ate. due to the chemicals, pesticides and animal feces used in modern agriculture, this is no longer possible. many plant based foods such as soy milk are supplemented with B-12 so getting enough is not an issue if one is consuming a well balanced plant based diet.

          what your argument does not take into account is that even though you yourself admit that humans do not need to consume animal flesh, milk or eggs, but doing so contributes to the suffering and brutal murder of innocent others. even 1-5% of flesh you suggest was produced through by 100% of misery and death to the farmed animal who was killed to provide it.

          finally, the saturated fat and cholesterol inherent in all animal based foods is a FAR bigger detriment to our health than taking a supplement once in a while or consuming supplemented foods.

          • Hi Markgil, thanks for your reasoned reply. I’ve read the Milton Mills MD article several times; here’s a link you might find interesting, from the Vegetarian Resource Group :
            I’ll have to research whether meat needs to be cooked or not; I know some raw foodists who eat it raw, not sure how much of it. I’m aware B12 is produced by bacteria, and yes, dirty food has more than cleaned, but from what I’ve read, still in insufficient amounts to keep humans healthy. You mentioned “contributes to the suffering and brutal murder of innocent others.” This suffering part is basically true; most people would not be interested in paying more for free range chickens or cattle over farmed, and I imagine chickens, goats, etc. would rather be in a field than a cage. At what point of consciousness does suffering stop? chickens? insects? bacteria? I don’t have the answer. I disagree with the “brutal murder” part, though. Their deaths are rather quick and painless as I understand it, vs. being chased, caught, and torn apart by predators. I also agree with your last point, saturated fats are a bigger health problem. The main point I was trying to make, though, is that humans are most likely omnivores, not that vegans are unhealthy.

          • It really doesn’t matter whether one argues if we are omnivorous or herbivorous. I think your last comment here misses the point Michael. The point is that we can get all the nutrients we need from plants and plant foods. As for suffering, you seem intent on blurring the all important distinction between sentient beings and non sentient beings. The ethical vegan draws the line at the animals we know are sentient. Bacteria is not a sentient life form. Plants are not sentient life forms. Insects are not as far as we know. “A sentient being is a being who is subjectively aware; a being who has interests; that is, a being who prefers, desires, or wants. Those interests do not have to be anything like human interests. If a being has some kind of mind that can experience frustration or satisfaction of whatever interests that being has, then the being is sentient.

            We engage in speciesist thinking when we claim that a being must have a humanlike mind to count morally. That is, it is speciesist to claim that a being must have a reflective sense of self awareness, or conceptual thought, or the general ability to experience life in the way that humans do in order to have the moral right not to be used as a resource. As long as there is someone there who is subjectively aware and who, in that being’s own way, cares about what happens to him or to her, that is all that is necessary to have the moral right not to be used as a resource.

            Is there uncertainty as to where the line is between sentient and nonsentient? Of course there is. It is, however, clear beyond any doubt that all of the animals that we routinely exploit – the fish, cows, pigs, sheep, goats, chickens and other birds, lobsters, etc. are sentient. So we know everything we need to know to make the moral decision to stop eating, wearing, or using those animals.” — Gary Francione

            – See more at:

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