Carnivore, Omnivore, or Herbivore?

Humans have always eaten meat… right? No, actually we haven’t. The best evidence for what we’re optimized to eat is our digestive system, so let’s examine it.

The teeth of a carnivore are long and pointed, for tearing raw flesh. Herbivores have flat teeth and flat back molars to grind their food. Carnivores do not have flat back molars at all.  Some herbivores do have small, what we call “canine” teeth for biting into tough plants (like apples) but these are nothing compared to the size and shape of a carnivore’s teeth. True omnivores’ teeth are most similar to carnivore teeth.

tigerteeth crocteeth

True Omnivores* (Bears eat fish and berries, Rats scavenge nearly everything from grains to veggies to meat):
bear_teeth rat_teeth

horse-teeth orangatang-teeth

Which look most like yours?

*By “true omnivore” I mean animals that naturally eat both plants and animals. For example, cats eat vegetables (in their commercial cat food, or maybe it’s handed to them under the table) but cats are not true omnivores, they are carnivores. In the wild, cats would eat birds and rodents, not leaves and berries.

The jaws of carnivores move up and down, but not side to side. The jaw motion of an omnivore is similar. They don’t chew. This is because carnivores tear off meat and swallow it whole. An herbivore’s jaw moves both up and down and side to side for grinding vegetation. Check your jaw and see what it does.

A carnivore or omnivore has small salivary glands in their mouth and their saliva does not contain digestive enzymes. Herbivores’ saliva is alkaline, containing carbohydrate digestive enzymes to pre-digest plant food. Herbivores also have large, developed salivary glands in their mouth. Human saliva is alkaline and contains digestive enzymes. And our salivary glands are large.

From an article by John A. McDougall, M.D.:

“Cats are obligate carnivores – they must live on a diet primarily of meat – and their taste buds reflect this by having abandoned the tongue sensors that respond to sweet-tasting carbohydrates.  Dogs are omnivores – they have retained both kinds of taste buds – those enjoying carbohydrates and amino acids.  Humans tongues respond pleasurably to sweet (carbohydrates), but have lost the taste for amino acids, placing us undeniably in the category of herbivores (plant eaters).”

Additionally, herbivores drink by sucking water up into their mouths as opposed to lapping it up with their tongue which all carnivores do.

A carnivore’s or omnivore’s small intestine is 3 to 6 times the length of its trunk. This is designed for rapid elimination of food that rots quickly. An herbivore’s small intestine is 10 to 12 times the length of its trunk, and winds itself back and forth in random directions. This is designed for keeping food in it for long enough periods of time to extract all the valuable nutrients and minerals before the food enters the large intestine.

A carnivore’s or omnivore’s large intestine is relatively short and simple, like a pipe. This passage is also relatively smooth and runs fairly straight so that fatty wastes high in cholesterol can easily slide out before they start to putrefy. (This is why it’s impossible for carnivores to get cancer or heart disease from high cholesterol and clogged arteries.) An herbivore’s large intestine, or colon, is puckered and pouched, an apparatus that runs in three directions (ascending, traversing and descending), designed to hold wastes that originally were foods high in water content. This is so that the fluids can be extracted from these wastes, now that all the useful nutrients and minerals have been extracted. Substances high in fat and cholesterol that have been putrefying for hours during their long stay in the small intestine tend to get stuck in the pockets that line the large intestine. (Vegetarians have lower rates of colon cancer.)

Care to guess which type of intestines we have? (Hint: Human small intestines are about 10 times our torso length and our large intestines are puckered.)

A carnivore can eat rotting, bacteria-ridden flesh completely raw without getting sick. They have stomach acids that kill the bad stuff and allow them to digest the rest without puking their guts up. Their stomach secretes powerful digestive enzymes with about 10 times the amount of hydrochloric acid than that of a human or herbivore. The pH of a carnivore’s stomach is around 1-2 (highly acidic) with food in the stomach. For herbivores and humans, the pH ranges from 4 – 5 with food in the stomach. Hence, man must cook his meats. Ever try to eat road kill? Or a freshly dead chicken, completely raw? Give it a shot and let me know how it works out for you. E. Coli bacteria, salmonella, campylobacter, trichina worms, parasites, or other pathogens would not survive in the stomach of a lion.

Animal flesh is composed of the most highly complex type of protein and requires vast amounts of uric acid to process. Uric acid is released into the system in amounts necessary to break proteins down into amino acids. Uric acid is a toxic substance responsible for the aging process and must be flushed out and dealt with. That is one of the jobs of the liver. In relative terms, a carnivore’s liver is a tool designed with the capacity to eliminate ten times as much uric acid as the liver of man or other plant eaters.

Our anatomy and digestive system clearly show that we must have evolved for millions of years living on fruits, nuts, grains, and vegetables.

Still skeptical?

Physical features
Carnivores and omnivores have physical characteristics which enable them to chase, trap, and kill. Speed, sharp teeth, and claws are tools meant to hunt, kill, and rend tough flesh. Examine your hand, fingers and fingernails. Is this an apparatus properly designed for catching, trapping, killing, and ripping apart cattle, hogs, chicken and fish? (How do they work for picking fruit from trees or harvesting vegetables?) Meat eaters have the speed and reflexes to catch prey. You do not. Try to catch an animal that doesn’t want to be caught (without tools or weapons) and you’ll get an idea of what type of hunter we naturally are.

Meat-eating animals that hunt in the cool of the night and sleep during the day when it is hot do not need sweat glands to cool their bodies; they therefore do not perspire through their skin, but rather they sweat through their tongues. On the other hand, vegetarian animals, such as cows, horses, zebras, deer, etc., spend much of their time in the sun gathering their food, and they freely perspire through their skin to cool their bodies.

Carnivores sleep the most, herbivores the least, and omnivores in the middle. Guess which group our own sleep correlates with.

Here are some charts from an article in Nature. They have stuck us (and other primates) in the omnivore group but notice that we’re at the extreme end of that chart, with nearly every other single omnivore sleeping more than we do. However, we fit nicely in the herbivore chart. A prominent dot for humans is added to the herbivore chart to show how we fit in at eight hours a night.

Carnivores (most sleep):


Herbivores (least sleep):

It is obvious that our natural instincts are non-carnivorous. Natural meat eaters find the smell of blood and dead animals attractive. How do you think they smell?

Carnivores kill without sympathy or remorse. Humans (obviously) do not.

One scientist explains it this way: “A cat will salivate with hungry desire at the smell of a piece of raw flesh but not at all at the smell of fruit. If man could delight in pouncing upon a bird, tear its still-living limbs apart with his teeth, and suck the warm blood, one might conclude that nature provided him with meat-eating instinct. On the other hand, a bunch of luscious grapes makes his mouth water, and even in the absence of hunger he will eat fruit because it tastes so good.”

Unlike other animals, humans can act outside of instinct. Other animals are programmed to know what food is. We are not. For us, it’s learned behavior. Or, in the beginning, guessed behavior. We can make choices about what we eat even if that’s contrary to good health (as millions prove every day when they eat at McDonald’s). When our ancestors ate meat, they were being human and making choices, rather than acting on instinct. Think about it: Do you really believe that cavemen were true experts about nutrition? If so, what other major decisions about your life would you like to put in the hands of a caveman?

In general, plant-eating creatures have the longest lifespans. Elephants, horses, and chimpanzees are at the top of the list while lions, tigers, and wolves are about half that. Humans’ lifespans are even longer than the elephants (even before modern medicine), providing more evidence that we’re in the plant-eating camp.

Science and medical evidence overwhelmingly shows that the more meat we eat, the sicker we get – heart disease, cancer, diabetes, osteoporosis, and every other major degenerative disease. If eating meat were so natural, it wouldn’t destroy our health.

Dean Ornish, M.D. was the first person to prove that heart disease can be reversed, and he did so by feeding his patients a vegetarian diet. John McDougall, M.D. has also written extensively about how animal foods cause disease, and how people can regain their health by eating vegan instead. The esteemed T. Colin Campbell oversaw the most massive study of the relationship between diet and disease, the China Study, which the New York Times called “the grand prix of epidemiology.” His conclusions are the same as the other experts: we’re not designed to eat animal foods, because we get sick when we do.

The fact that health can be regained by laying off meat and dairy is powerful evidence that we shouldn’t have been eating those foods in the first place.

By now, the meat-eating reader already has objections.
Let me try to address some of these.

Objection 1: We’re capable of eating meat, therefore we’re omnivores.
Cats are also capable of eating both plants and meat.  In fact, some people feed their cats a purely vegan diet.  But cats are not omnivores, they are carnivores (as previously explained). True omnivores are not just capable of eating both plants and animals, but their bodies are optimized for it. Just because we can digest meat doesn’t mean that we’re supposed to. We can digest cardboard, but that doesn’t mean that we should.

Objection 2: Vitamin B12 is only obtained from meat, dairy, and eggs.
B12 isn’t made by animals, it’s made by bacteria. It’s found where things are unclean (and rotting flesh is dirty).  This easily explains why historically it’s been easy to get B12, because until recently we didn’t live in a sanitized environment. Pull a carrot out of the ground and don’t wash it properly, and there’s almost certainly some B12 there. Vegans should take a B12 supplement, not because veganism is unnatural, but because the modern diet is too clean to contain reliable natural sources of dirty B12.

Incidentally, our need for B12 is tiny: 3 micograms a day (not milligrams, micrograms). The amount of B12 you need for your entire life is smaller than four grains of rice.

Objection 3: Other primates eat meat.
Hardly. A chimp’s diet is 95-99% plant foods, and the non-plant food isn’t meat, it’s termites. We also have to remember that primates are intelligent and can make choices outside of instinct, just like humans do, so the tiny amount of non-vegetarian food they might eat could simply be due to choice, not instinct.

Others? Leave a comment.

Breakfast: An awesome smoothie! Banana, pear, kale, and hemp milk.

Lunch: Leftover vegan pizza, blueberries, and an orange
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Dinner: Mexican food! Enchilada, vegan beef taquito, soy chorizo taco, and vegan queso (I add salsa to this recipe)

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106 thoughts on “Carnivore, Omnivore, or Herbivore?

  1. Martin smith

    We are omnivore like chimps and gorillas !!!! but some people can eat more meet some more vegetables, that’s it. Ancient olmecs probably extinct because of eating corn. People in US on the begining they had the same problem with corn and beans without fat in one meal…. I personally and people from my family we prefer to have more meet, I feel bad half day after bigger amount of vegetables especially on morning, Iv’e tried everything from “normal ” vegetables and exotic and “superfood” /superballox.
    Simple fact ( I know a little bit disgusting just for science) :if you eat chicken salad with vegetables (corn , onion, carrot, cabbat) and you will vomit it after 1.5-3h what you going to vomit? of course vegetables , because chicken is already digested. greetings

  2. Rob Cairns

    Chimps hunt monkeys for meat. They love the taste of it. It’s a fact. They’ve even been known to take and consume children. The vast majority of studies that link food with illness link carbohydrates not meat. Sugar, cereals and grains are terrible for body. Lastly, obesity is linked with excess carbs not meat or good fats. Vegetarians suffer the same illnesses as meat eaters.

  3. Emilie

    The above comment is pure ignorance. Chimps and Gorillas are simply NOT Omnivores. And the pathetically biased article about couple and their vegan baby? Really, come on now. A well-planned vegan diet is the healthiest possible diet for humans of all ages. Finally I have to say the one thing this article is off on is; While we have many similarities to Herbivores, humans are actually a *Frugivore species, rather than Herbivore.

  4. victoria

    Human’s do not eat meat. Hope your heart disease/stroke/diabetes/(disease/sickness) goes well. We are functionally not carnivore so stop acting like you are. You’ll soon feel the benefits when you eat what you’re designed to eat- plant based and NOT MEAT.

  5. Alex

    You know when you read something and it uses random bits of science that it’s cherry picked to make it sound more correct and it *almost* manages to come off as convincing… Yeah this is a great example.

    Nobody argues that we do not originally descend from a herbivorous species rather than a pure carnivore, there would be no reason to develop molars if that was the case. Our digestive systems are the result of millenia of evolution and are designed to take anything we eat, vegetable or meat. If we only evolved the ability to mildly process meat but not optimised to survive on it we would be like an inverse-panda; eating tonnes of the stuff and passing it out mostly undigested. Since it is more than possible to survive indefinitely based on a almost pure-meat, zero-veg diet (Eskimos living in the Arctic circle) the idea that we are ‘not built’ to survive on meat is ridiculous.

    Also saying that *herbivores live as long as we do* as proof we should be vegetarian is highly misleading and just plain biased. A wolf might only live 15-20 years but a sheep will live 12-15. A cow only lives 15 while a polar bear can reach 40. Elephants are one of the longest lived mammals… alongside almost every species of whale which are pretty much entirely carnivorous. Lifespan does not imply a better diet otherwise we should all be eating plankton like the jellyfish.

    Our instincts aren’t to hunt and kill?! What part of humanity have you been watching? We are clearly a predator, even today our society is built on aspects that wouldn’t make sense unless we were dealing with our instincts to hunt. We don’t have ‘weapons’ because we haven’t needed them; evolution has selected for tool use over ‘natural’ weapons, that doesn’t make us any less of a predator. We are one of the few species known as a persistence hunter, we literally chase prey until it keels over from exhaustion (which btw is a reason we kept our ability to sweat, we don’t have to stop to get our breath back while panting). Also the reason we are ‘squeamish’ about killing is because we personify animals; “Nooo, don’t kill the pig, his name’s spider-pig!”. Get rid of that emotional attachment and we are more than happy to slit an animals throat for dinner – it’s modern society, not instinct that makes killing hard.

    As for the ‘we cant deal with raw meat’ argument, 2 things:

    1) Neither can the carnivores. They are riddled with bugs and parasites caught when eating raw/rotten meat, they catch them just as much as we do, stomach acid or no.

    2) We eat raw meat all the time. Ever been with someone that orders a blue steak? The reason we don’t like *rotten* meat is we can smell it’s bad and have developed an aversion to it. Smell a fresh steak (or go cut your finger and smell the blood) and it won’t smell vile unless you convince yourself it *should.

    The reason we don’t eat raw meat all the time (and do struggle with it) is down to evolution. We ate raw meat (like other primates) but after the invention of fire we no longer needed to. Cooked meat offers a safer, easier to digest (so more accessible) source of calories than raw meat so over time the ability to handle bad meat diminished. However we can still eat any animal raw; fish, beef, pork & chicken are all safe to eat raw as long as the animal was healthy and the meat is kept fresh (time is a bigger enemy than the meat itself).

    Speaking of cooking; we cannot feasibly survive on a pure raw vegetarian diet long term. The major staples of vegan diets (grains, pulses, beans) are all basically worthless as the calories burned to digest them would render eating them a waste of time. Sure, you could live off of fruits, nuts and berries but how well? And how many of us could? Society and technology would never have progressed past the stage chimpanzees exist at. It is a universally accepted fact that learning to cook meat is what allowed humans to develop our brains to the way they work now, without eating meat that would never have happened and we likely would have died out (like many of our herbivorous cousins have throughout history).

    We might not be perfect meat eating machines (no animal is) but it is clear we are more than capable of eating, digesting and thriving on meat – it’s the reason we are where we are today.

  6. BoBo

    what the f? this so biased its not even funny humans have a digestive system ~ 6x their height which falls into omnivore category
    humans have stomach ph of 1.5-3 which again falls into omnivores

    don’t listen to these lies please its ok to be vegan but not to lie like this

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