Are human bodies designed to eat meat?

Many people describe themselves as ‘omnivores’ – meaning they eat a wide variety of food from plant-based and animal-based sources. Meat-eaters will often argue the presence of ‘canine teeth’, as well as our ability to digest meat means nature designed us to consume flesh. But is this true? Does human physiology support the idea that human beings are omnivores?

In his book Should We Eat Meat?: Evolution and Consequences of Modern Carnivory, author Vaclav Smil writes: “In traditional societies, meat eating, more than the consumption of any other category of foodstuffs, has led to fascinating preferences, bans and diverse foodways; and modern western agricultures are obviously heavily meat-oriented.

“In nutritional terms, the links range from satiety afforded by eating fatty megaherbivores to meat as a prestige food throughout the millennia of preindustrial history to high-quality protein supplied
by mass-scale production of red meat and poultry in affluent economies.”

But this is what’s known as behavioural omnivorism – the creation of meat-eating through cultural reinforcement and habit, rather than dietary need. A useful exercise when trying to answer the meat question is comparing our bodies to those of natural carnivores – for example, lions, and natural herbivores like gorillas. In his essay The Comparative anatomy of Eating, Dr Milton R Mills states: “Mammals are anatomically and physiologically adapted to procure and consume particular kinds of diets. It is common practice when examining fossils of extinct mammals to examine anatomical features to deduce the animal’s probable diet. Therefore, we can look at mammalian carnivores, herbivores (plant-eaters) and omnivores to see which anatomical and physiological features are associated with each kind of diet.”

Dr. T. Colin Campbell is a professor at Cornell University in New York, and author of The China Study. He claims the eating of meat is a relatively recent phenomenon in human development, saying: “The birth of agriculture only started about 10,000 years ago at a time when it became considerably more convenient to herd animals. This is not nearly as long as the time that fashioned our basic biochemical functionality (at least tens of millions of years) and which functionality depends on the nutrient composition of plant-based foods.”

Before the birth of modern agriculture, humans had to hunt all prey. But Dr Neal D. Barnard, founder and president of the Physicians Committee for Responsible Medicine claims humans lack the basic abilities to be good hunters. “We are not quick, like cats, hawks or other predators. It was not until the advent of arrowheads, hatchets and other implements that killing and capturing prey became possible.”

And when it comes to eating flesh, anthropologist Dr Richard Leakey says: “You can’t tear flesh by hand, you can’t tear hide by hand.” In addition, animal rights charity Peta claims we don’t have the right teeth. According to a Peta spokesperson: “Humans have short, soft fingernails and small, dull canine teeth. All true carnivores have sharp claws and large canine teeth that are capable of tearing flesh without the help of knives and forks. Real carnivores’ jaws move only up and down, enabling them to tear chunks of flesh from their prey. Humans can move their jaws up and down and from side to side, and we also have flat molars (which carnivores lack), allowing us to grind up fruit and vegetables with our back teeth like herbivores do.”

Or, as Dr Mills puts it: “Human teeth are similar to those found in other herbivores with the exception of the canines – the canines of some of the apes are elongated and are thought to be used for display and/or defence. Our teeth are rather large and usually lean on one another. The incisors are flat and spade-like, useful for peeling, snipping and biting relatively soft materials.

“Carnivores have short intestinal tracts that allow meat to pass quickly through their digestive system.”

“The canines are neither serrated nor conical, but are flattened, blunt and small and function like incisors. The premolars and molars are squarish, flattened and nodular, and used for crushing, grinding and pulping non-coarse foods.”

The composition of human saliva also suggests we are designed to primarily ingest plants. It contains the carbohydrate-digesting enzyme, salivary amylase, which is responsible for the majority of starch digestion. Once the breakdown of food starts in the mouth, our oesophagus is narrow and suited to small, soft balls of thoroughly chewed food.

On top of this, our digestive systems struggle to handle meat – and this is due in part to the length of our intestinal tract. Carnivores have short intestinal tracts that allow meat to pass quickly through their digestive system. Dr Mills claims: “Striking differences between carnivores and herbivores are seen in these organs. Carnivores have a single-chambered stomach. Because meat is relatively easily digested, their small intestines (where absorption of food molecules takes place) are short – about three to five or six times the body length. Since these animals average a kill only about once a week, a large stomach volume is advantageous because it allows the animals to quickly gorge themselves when eating, taking in as much meat as possible at one time which can then be digested later while resting.”

Carnivores stomachs secrete hydrochloric acid, meaning their gastric pH levels are maintained at around 1-2 even with food present, which is necessary to facilitate protein breakdown and to kill all the dangerous bacteria often found in decaying flesh foods.

In contrast, herbivores have significantly longer guts than carnivores because of the relative difficulty with which various kinds of plant foods are broken down, due to large amounts of indigestible fibres. The small intestine of plant-eating animals tends to be very long – over ten times body length – to allow enough time and space for absorption of the nutrients.

“Man’s stomach is single-chambered, but only moderately acidic,” explains Dr Mills. “Clinically, a person presenting with a gastric pH less than 4-5 when there is food in the stomach is cause for concern. The stomach serves as a mixing and storage chamber, mixing and liquefying ingested foodstuffs and regulating their entry into the small intestine. The human small intestine is long, averaging from 10 to 11 times the body length.”

“Humankind does not show the mixed structural features one expects and finds in anatomical omnivores such as bears and raccoons.”

So like other herbivores, humans have much longer intestinal tracts – giving the body more time to absorb nutrients from plant-based foods, as well as breaking down fibre.

Another interesting comparison between carnivores and herbivores is the ability to break down bacteria in raw meat. Peta claims: “True carnivores gulp down chunks of raw flesh, relying on their strong stomach acids to break it down and kill the dangerous bacteria in meat that would otherwise sicken or kill them. Humans have much weaker stomach acids that are similar to those found in animals who digest pre-chewed fruits and vegetables. Without carnivorous stomach acids to kill the bacteria in meat, dining on animal flesh can give us food poisoning.

“According to the U.S. Department of Agriculture, meat is a significant cause of foodborne illness. Every year in the U.S. alone, food poisoning sickens more than 48 million people and kills more than 3,000. Because of this, we must cook meat to make it easier to digest and to destroy bacteria.”

Dr Mills says: “In conclusion, we see that human beings have the gastrointestinal tract structure of a ‘committed’ herbivore. Humankind does not show the mixed structural features one expects and finds in anatomical omnivores such as bears and raccoons. Thus, from comparing the gastrointestinal tract of humans to that of carnivores, herbivores and omnivores we must conclude that humankind’s GI tract is designed for a purely plant-food diet.”

One of the most frequently levelled questions at vegans is: where do you get your protein? Many people think a meat-free diet means a protein-free diet. Of course this is not the case, with a number of grains and vegetables easily providing a healthy level of this macronutrient.

A more pressing issue is the problem of omnivores eating too much protein. According to China Study author Dr Campbell: “In the next ten years, one of the things you’re bound to hear is that animal protein is one of the most toxic nutrients of all that can be considered.”

Eating too much protein can result in nutritional deficiencies, increase the risk of developing heart disease, and worsen kidney function in those with kidney disease – debunking the myth humans needs huge amounts of protein to thrive.

The American Academy of Nutrition & Dietetics is considered to be the foremost authority on diet and nutrition it the USA. For several years now (since 2009) it has held the position that meat is not necessary for human diets. It says: “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.”

“Not only is meat unnecessary for humans, it is unhealthy”

Peta goes one step further – claiming not only is meat unnecessary for humans, it is unhealthy: “Carnivorous animals in the wild virtually never develop heart disease or suffer from strokes—ailments that humans can suffer an increased risk of developing due to their consumption of the saturated fat and cholesterol found in meat. Heart disease is the number one killer in the U.S., according to the American Heart Association. If humans were meant to eat meat, why do meat-eaters have a 32 per cent higher risk of developing heart disease than vegetarians?”

Dr. William C. Roberts, editor of the American Journal of Cardiology, adds: “Although we think we are, and we act as if we are, human beings are not natural carnivores. When we kill animals to eat them, they end up killing us, because their flesh, which contains cholesterol and saturated fat, was never intended for human beings, who are natural herbivores.”

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  1. Wendy on June 25, 2017 at 5:11 pm

    I’m pro vegan, but this article, while interesting, avoided talking about omnivores or the fact that gorillas also eat insects. Also, much of the illnesses caused by eating undercooked meat is due to how it’s processed. Humans have successfully eaten raw flesh without sickness (sushi and steak tartare). While I fully support a vegan diet and strive to follow one myself, I hate reading vegan articles which scream bias instead of looking at a picture as a whole. Instead I’d rather read an article that highlights health benefits of the diet and human physiology rather than comparing us to lions and gorillas.

  2. Alastair on March 7, 2019 at 12:14 am

    Tiny Insects are hardly the same as a small mammal or a deer. Lions and tigers don’t eat insects, does this mean they’re not true carnivores? Steak tartare is cut up cleaned meat, and processed into tiny pieces. Sushi has carefully selected small pieces or slivers of certain fish. Do you think carnivores have access to processed pre-cut meat like this in the wild Wendy? So imo the points you made don’t make much sense, and in no way prove anything. Lest of all the accusation of bias by the author.

  3. Kayden on June 21, 2019 at 1:38 am

    I wonder how Milton would reconcile the fact that human stomachs have a PH range of 1.5-3 depending on conditions. Our stomach PH has more in common with carrion eaters than cows.

    Also interesting is that the human appendix (called the cecum) is present in pretty much all animals. In obligate omnivores (rear gut digesters), it’s where bacteria live that break down cellulose into saturated fat. It also tends to be quite large in herbivores. It’s rather small in carnivores unsurprisingly- almost non existent in humans and can even be removed without ill effect.

    Then, if you take all the primates and arrange them by gut to body size, the predominantly vegetarian gorilla is at one end of the spectrum with the largest digestive tract (and smallest brains) and humans at the other with the smallest digestive tract relative to body size (and largest brain).

    Someone might want to spend a bit more time fact checking this guy.

    • Joey on October 28, 2019 at 7:00 pm

      Yup. I was a vegan at some point… but this guy’s facts are just plain… false.

      • Vegan on August 12, 2020 at 2:36 pm

        You cant stop being vegan. You are either for animal cruelty or against it. It is not something you switch on and off

  4. Joey on October 28, 2019 at 6:57 pm

    So pre agriculture people were able to “plan” their diets?

  5. mark king on March 8, 2020 at 9:05 pm

    Human stomach acid is 1.5 that of a scavenger, its that acidic to kill unwanted bacteria. I would suppose as one of the only animals that willingly mixes its food sources in one meal the stomach will struggle. Eat meat on its own and it has no such problems, same with fruit and carbs, just don’t mix the three.

    • Yumnam Linthoisana on March 29, 2020 at 10:01 pm

      “The small intestine of humans is long, averaging 10 to 11 times the body length.”
      Whoa! Whoa! Wait, what? The small intestine of humans is 6m long. Almost all people fall within the height range of 1.5m to 2m. Divide 6 by 1.5 and you get 4. Divide 6 by 2 and you get 3.
      What I’ve learnt from the vegan and animal rights movement is that vegans don’t know proper vocabulary, don’t have basic knowledge of biology, physiology and chemistry and now I learn they can’t do simple maths.

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