We Are Carnivores - A Closer Look At Human Digestive System


It is often touted by vegan groups and vegan doctors that we are herbivores. This is simply ridiculous. They produce all sorts of comparisons between humans, herbivores and carnivores claiming that most of our physiological and many anatomical features are like those of herbivores and dissimilar to that of carnivores. But most of their cherry picked information is either meaningless, unscientific or downright false! if we dig a little deeper we find that our digestive system is ideally suited to the digestion of animal sourced food and that we cannot efficiently handle or even nourish ourselves on plant matter.

Ruminants and Humans

No Vertebrates (which includes mammals) produce cellulase - the enzyme needed to break down plant fibre - so how do herbivores extract energy and nutrients from plant matter? Herbivores are animals that specialise in eating plant matter. It doesn't mean they never eat animal matter because even horses and cows have been seen eating small animals but they derive most of their energy and nutrients from plant sources. Clearly we are not ruminants like cows or sheep and I hope nobody would argue with that. Ruminants have multiple stomachs in which a host of specialised cellulase producing microbes ferment and break down the plant fibre. They regurgitate and re-chew the grass hundreds of times to extract the nutrients and break down the fibre so that they can convert it to fatty acids because fatty acids are their main source of energy... of calories. They eat all day to sustain themselves because plant food is a low quality nutrient source which requires huge bulk quantities and a lot of fermentation to extract energy from it. Humans simply don't have the digestive apparatus and the specialised microbes to breakdown plant matter and efficiently extract energy from it.

The Four Stomachs of a Ruminant

Here are the main arguments that are obsessively pushed by vegan articles and doctors when comparing humans to carnivores:

We Don't have Claws, Sharp Canines and Locked jaws Like the Carnivores

They proclaim: 'We don't have large sharp canines; we don't have claws and we don't have large jaws that are locked in an up and down articulation to kill our prey and tear the flesh out.' That's a ridiculous point! Humans have a ten times larger brain to body ratio than lions as well as hands to use tools, to catch and eat prey. Even chimpanzees catch their monkey prey with bones and stones using their hands to tear the flesh out. We didn't need to evolve claws or teeth - that would have been a wasteful and costly process.

Human Stomach Acidity is weak like that of the Herbivores

And then it is claimed that unlike carnivores we have a weak stomach PH like that of herbivores. This is false! Our Stomach PH is around 1.5; highly acidic, in fact more acidic than most carnivores and only fractionally lower than scavenger birds (1.3). Primates and other herbivores have PH's around 4 or higher, which on the logarithmic PH scale is hundreds of times weaker than humans. A strong PH is the mark of a carnivore - ideal for breaking down meat. A low acidic PH is also vital for carnivores and scavengers as it kills pathogenic bacteria and parasites on contact before they enter the system. Note that humans have a much lower PH than even omnivores and cats (PH 3.6)!

Intestinal Length to Body Ratios Compared

Another point the vegan preachers push is that our intestinal length to body length ratio is closer to a herbivore's. That's incorrect. In fact The human gut with its simple stomach, relatively elongated small intestine and reduced caecum and colon, does not fit any one group but lies between the herbivores and carnivore groups. And yes we do have longer small intestines than carnivores but then we have a 10 times larger brain to body ratio than lions. Our brains are energy demanding. Our extraordinarily large brains use up 25% of the bodies total energy needs so we needed that extra small intestine length to extract even more energy from animal fat to feed our thirsty brains. Only energy dense, readily abs Once again, it is too simplistic to compare humans to other animal as we are very unique in many ways.

Non human primates and human digestion compared

So now the main argument left from the slightly more sophisticated vegan groups and doctors is that the human digestive system is very similar in proportion and function to that of the non-human primates who eat predominantly plants and fruits. But this couldn't be further from the truth. Let's have a closer look.

At a first glance, the proportions of the human digestive system seem very similar to that of other primates. The actual length of the small intestine and colon is similar but length is not equivalent to volume or surface area. The two cylinders below have identical lengths yet their volumes and surface areas are totally different. This is a crucial  factor when it comes to fermentation of plant fibre because a greater surface area allows for more  proper microbial action

                                          These Two Cylinders are of Equal Length but Different Surface Areas

Non-human primates have a fully functional caecum which is a microbial fermentation chamber in which cellulose is digested. In Humans the caecum has become an almost non-existent vestigial appendix. What's more the colon of primates is over twice as large in volume as that of humans. This is a crucial point because this is where further break down of plant fibre takes place with the help of a massive colony of microbes to convert the plant matter into short chain fatty acids. These fatty acids are the energy source of primates and ruminants. In humans not only is the caecum absent but the colon is much smaller hence our inefficiency at extracting energy and nutrients from plants.

The capacious colon and caecum of a gorilla or chimpanzee is totally vital for their survival on plant foods because it provides 57% of there energy requirements from the fermentation and conversion of plant fibre into fatty acids

Our small intestines however, are twice as voluminous as those of primates which is perfect for digesting nutrient dense meat, that is smaller in volume and easy to break down. This was an essential evolutionary move. We sacrificed overall colon volume for a greater small intestine volume to provide more readily available energy to our growing brain.

The human colon can only derive 2 to 9% of it's calories from the fermentation of fibres in the colon. Unlike the apes and ruminants, humans on a high fibre diet excrete almost all of the fatty acids in their faeces. Clearly, humans are not specialised plant eaters - our use of fibre is inefficient and costly! The irony is that even gorillas are on a high fat low carb diet because they derive 60% of their calories from fatty acids and only 24% from carbohydrates. But they get it from colon fermentation . Humans don't have the surface area or the microbes to do this.

Gorillas have to eat around 40 pounds of fruit and plant matter a day just to sustain themselves. Plants are a low quality source of food that's why volumes of it are needed. If we were actually herbivores (which we aren't) we would have to eat all day. That's absurd. Meat and animal sourced food is nutrient dense and contains all the essential nutrients in bioavailable form provided one eats it from head to toe including the offals.

There are hundreds of millions of americans walking around with part or all of their colons removed but a gorilla or chimp would starve to death without a colon. Clearly humans have a totally different digestive system to those of non-human primates. We don't and cannot use fibre as our main source of fuel.


The idea that humans are herbivores is preposterous. Humans simply don't have the mechanisms and apparatus to extract energy and sufficient nutrition from plants.

Humans are meant to eat animal sourced foods. In our evolution we sacrificed the large colon and fibre fermentation of our primate ancestors and developed larger small intestines and a strong stomach PH in order to derive all our nutrients and energy from animal fats and animal protein. This was a necessary trade off to feed our energy demanding brains.


There are many other issues with a plant based diet which make the absorbability and assimilation of nutrients even worse. Although these topics will be the subject of future articles, a brief mention of them here is important.


Many of the so called health claims of dietary fibre have not been proven. fibre is a major irritant of the gut - even the American Dental Association know this as they caution against eating more than 25 to 35 grams of fibre because of possible gastro intestinal distress and blockages. And many are debunking the myth that fibre is at all necessary for a healthy human gut. Many studies have in fact shown that excessive intake of fibre is detrimental to health particularly gut health.

The Missing Nutrients in Plants

Many vital nutrients can only be found in animal sourced food like vitamin K2, Vitamin D, DHA, cholesterol, heme-iron, Vitamin A and B12. Without supplementation, vegans are low in these along with zinc, ferritin and iodine . But if supplementation is required, how can it be called a natural diet? What's more, the efficacity of supplementation is dubious. A vegan and to lesser extent vegetarian diet is not sustainable. Animal sourced foods contain all the necessary nutrients for a healthy body.

Anti-Nutrient Toxins Found In All Plants

Maybe the most devastating part of a plant based diet is the presence of countless anti -nutrients. Plants are chemical factories that have developed numerous strategies to ward of predators. They are loaded with all kinds of anti-nutrients - you could say poisons - which prevent the absorption of minerals and create slow carnage in the blood and organs. As a point in case spinach. kale, peanuts almonds beet greens, sweet potatoes, chocolate, rhubarb and many others contain oxalic acid which accumulates in the organs and brain in glass like crystal chards. It is linked among others to kidney failure, arthritis, inflammation and even autism. 10 to 25 grams of oxalic acid can kill a grown person. Of course There are many other anti nutrients toxins in plants which will be the subject of another article.

Our Gut : Unlike other Great Apes, specialized for Eating Meat, Not Plants


Chart comparing intestinal to body length ratio


A compelling talk on human digestive system compared to primates and anthropological considerations:



Brilliant you tube comparing human digestive system to that of Gorillas:


Scientific analysis of primate digestion:


Primates often switch diets and often make substantial use of animal flesh:


Comparing gut volume sizes of primates and humans:




comparisons and discussions on stomach acidity in different animals:



Humans might not fare too badly on a scavenger's diet of high meat due too low acidic stomach Ph: