Are Humans Omnivores?
The idea that humans are omnivores is used as a justification for consuming animal products today. And then veganism is portrayed as an unnatural sacrifice that “extremists” make for animals!
But this is actually incorrect. Humans are not anatomically omnivores.
Humans are anatomically frugivores.
“Frugivore” is defined as “an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds.” Although “frugivores” and “herbivores” are both plant-eaters, the main difference is that herbivores eat mostly leafy vegetation while frugivores eat more plant appendages such as fruits, nuts, seeds, etc. “Frugivore” and “herbivore” can be used somewhat interchangeably, but the most important concept is that they are both plant-eaters.
Anatomical Attributes of Humans
Humans have no specialized anatomical adaptations to eating meat, dairy, or eggs. By contrast, we have many adaptations to eating plants.
“Although most of us conduct our lives as omnivores, in that we eat flesh as well as vegetables and fruits, human beings have characteristics of herbivores, not carnivores (2). The appendages of carnivores are claws; those of herbivores are hands or hooves. The teeth of carnivores are sharp; those of herbivores are mainly flat (for grinding). The intestinal tract of carnivores is short (3 times body length); that of herbivores, long (12 times body length). Body cooling of carnivores is done by panting; herbivores, by sweating. Carnivores drink fluids by lapping; herbivores, by sipping. Carnivores produce their own vitamin C, whereas herbivores obtain it from their diet. Thus, humans have characteristics of herbivores, not carnivores.” NIH.
This comparison of carnivores and herbivores represents the two extremes on the spectrum. Omnivores lay somewhere in the middle and have a mixed anatomy. Meaning, omnivores will have some characteristics of carnivores and some characteristics of herbivores.
For instance, bears have claws as appendages (carnivore), they pant to cool down (carnivore), they suck to drink water (herbivore), and they have a long intestinal tract (herbivore).
Humans, however, have all the characteristics of herbivores.
Some other notable anatomical features of humans that point to our anatomy as being plant eaters are the movement of our jaws and trichromatic vision.
Jaws
Carnivorous jaws are locked into an up and down motion. They physically cannot move their jaws side to side. Their jaws and teeth are designed to shred flesh from a carcass and swallow. Plant eater jaws are designed to chew and grind for long periods of time. Plant eater jaws can move side to side and up and down, in order to grind and pre-digest plant matter in the mouth.
Vision
Carnivores are hunters. Their primary need for vision is to see movement of prey. They do not need to see color. Carnivores have dichromatic vision - they are essentially color blind - because they only need to see movement.
Frugivores (not herbivores) have trichromatic vision, which enables them to see color. This is evolutionarily advantageous because it allows them to see ripe fruits and vegetables. Herbivores, which eat mostly leafy plants, don’t necessarily need to see color because basically all leaves are green. True herbivores have dichromatic vision, just like carnivores. The trichromatic vision of humans is further evidence that separates us both from carnivores and true herbivores, and suggests we are indeed frugivores.
Cholesterol and Atherosclerosis
Cholesterol is an essential molecule for animal life. The main function of cholesterol is to maintain the integrity and fluidity of cell membranes and to serve as a precursor for the synthesis of substances such as steroid hormones, bile acids, and vitamin D.
It is so essential, in fact, that animals - including humans - manufacture their own cholesterol. Cholesterol is so important to the health of our cells that our bodies evolved to make all the cholesterol that we need.
Cholesterol only occurs in animals, plants have no need for cholesterol and do not manufacture cholesterol.
Our plant eater body’s manufacture of cholesterol exists in stark contrast to other nutrients like vitamin C. Vitamin C is essential for all animal life as well, and vitamin C only occurs in plants. Carnivores manufacture their own vitamin C, because they do not have a dietary source of it. Plant eaters, such as humans, do not manufacture their own vitamin C, because they have abundant dietary sources of it.
The point is, our bodies adapt to our evolutionary diet.
High cholesterol is widely recognized as one of the top three risk factors for atherosclerosis and heart disease. But high blood cholesterol in humans only occurs when we eat dietary sources of cholesterol and saturated fat. Saturated fat is abundant in animal foods, and very rare in the plant kingdom. Our bodies make just the right amount of cholesterol - any excess from dietary sources and our blood cholesterol levels start to rise, and atherosclerosis is instigated.
But interestingly, this does not happen in carnivores. Carnivores exclusively eat the flesh of other animals, and therefore consume massive amounts of dietary cholesterol and saturated fat. And yet, they don’t get atherosclerosis.
“Atherosclerosis affects only herbivores. Dogs, cats, tigers, and lions can be saturated with fat and cholesterol, and atherosclerotic plaques do not develop (1, 2). The only way to produce atherosclerosis in a carnivore is to take out the thyroid gland; then, for some reason, saturated fat and cholesterol have the same effect as in herbivores.” NIH.
Carnivorous bodies have a means of expelling excess cholesterol so that it doesn’t build up in their arterial walls and cause atherosclerosis. Their bodies developed this mechanism over millions of years of eating a carnivorous diet.
Plant eaters, however, do not have the ability to expel excess cholesterol from their bodies. Because evolutionarily, plant eaters don’t encounter dietary cholesterol. Their body simply makes the cholesterol they need, and there’s no excess cholesterol in their system.
Plant eaters develop high blood cholesterol and atherosclerosis when they consume a diet that is high in dietary cholesterol, and not consistent with their evolution.
Heart disease caused by atherosclerosis is the number 1 killer of Americans.
Atherosclerosis only affects plant eaters. Humans are dying of an epidemic of atherosclerosis. Humans are anatomically plant eaters.
Big Brains
Many people believe that eating meat is the reason our species have developed big brains.
And on the surface, this sort of makes sense…
Our brains require a massive amount of energy. Although our brains only constitute 2% of our total body weight, they consume as much as 25% of our total energy in a given day.
And meat is a concentrated source of energy, that is true. But the caloric energy in meat is exclusively derived from protein and fat. Meat does not contain any carbohydrates or glucose.
And what is the preferred source of energy for the human brain?
Glucose.
As evolutionary geneticist at University College, London, Mark Thomas puts it, the brain is simply “desperate for glucose.”
Eating meat could not have led to the development of a big brain, because it does not contain the optimal fuel for a big brain.
Glucose occurs exclusively in plants. But some plants contain more glucose than others.
Leaves have a low concentration of glucose. A true herbivore that is eating exclusively leafy greens must consume a massive amount of leaves to subsist every day. And even with adequate calorie intake, eating exclusively leaves does not provide enough glucose to feed a big brain like that of humans. This is probably why animals that eat exclusively leaves in the wild, such as giraffes, have not developed a big brain like humans.
Fruits have a higher concentration of glucose and calories than leaves. A frugivore that is eating a mixture of leaves, fruits, vegetables, nuts, shoots, etc is getting higher calorie and glucose concentrations in their food. This means they can spend less time eating while consuming more calories and glucose. This is why primates and great apes have the biggest brains in the animal kingdom.
Tubers such as potatoes, cassava, jicama, turnips, parsnips, yams, etc have a massive concentration of glucose. But there’s a problem: tubers and starchy vegetables contain resistant starch which is indigestible when raw.
But resistant starches are a powerhouse of glucose, in amounts that would be needed to evolve a big brain like our’s.
And that’s where cooking enters the picture.
It may sound odd, but cooking is actually a form of digestion. It’s categorized as “external predigestion.” Cooking predigests the resistant starches in tubers, so that the starches are already broken down by the time we eat them.
Think about eating a raw potato vs a cooked potato. The heat from cooking has broken down some of the structure in the cell walls so that we can chew and digest it. Cooking unlocks the resistant starches, that are full of glucose, in tubers and starchy vegetables.
So the discovery and utilization of fire, the ability to cook resistant starches, and the subsequent access to massive amounts of glucose is what allowed our brains to grow so big.
Cooked resistant starches, not meat, provided the fuel for our big brains.
And if we take a step back and think about this in comparison to other species, this totally makes sense.
Lots of other species eat meat, and they never developed big brains like us. Lots of other species eat plants, and they never developed big brains like us. Primates and apes are the only ones who have come close, because they eat foods that are abundant in glucose, but not as abundant as starchy vegetables. Cooking makes the difference. We are the only species on earth that has ever been able to utilize cooking to predigest our food.
Cooking meat does not change its molecular structure or make any nutrients more bioavailable. And whether or not it’s cooked, meat still does not contain glucose. And again, the preferred source of energy for our brain is glucose.
But as we’ve discussed, cooking resistant starches does change its molecular structure and does make massive amounts of glucose more available.
What has set us apart from all other animals and allowed us to develop big brains is the ability to cook and digest starchy vegetables.
In times of famine and emergency, our brain does have the ability to derive energy from ketones, which are acids formed when our body breaks down fat for energy. But this biological process only occurs when our bodies are starved of glucose, which is an emergency metabolic state. Ketones are not the preferred source of energy for the brain.
Fossil Record
In the 1930’s and 40’s, there were some amazing anthropological discoveries of early human remains that were found alongside animal bones and tools that very much looked like they were used to maim and kill animals. This led to an assumption that early humans ate a largely meat based diet. This bias has greatly influenced anthropological and nutritional research right up to modern day.
But this assumption that early humans ate a largely meat based diet is based on a false premise. Bones preserve well in the fossil record. Plants, especially plants that are partially eaten, do not. So on the surface, these sites seem to present nothing but humans and the animals they killed and ate. But after revisiting many of these sites with a new lens seeking fossilized plant matter, anthropologists are finding abundant evidence of plants surrounding the sites of early human fossils.
Because the fossil record favors the preservation of bones, this disproportionately skewed our perception of the balance of early human diets. Yes, early humans did kill and eat some animals, and their bones are found alongside the bones of early humans. But when we assess the totality of animal bones versus microscopic plant matter at these anthropological sites, it becomes clear that animal meat represented a tiny proportion of early human diets. The vast majority of the early human diet was plants.
Lactose
Human breast milk is the perfect food for babies. It’s been shaped by evolution for millions and millions of years to grow a helpless baby into a capable child. Although in modern western society most babies are weaned around 6 months to a year, traditional cultures typically breastfeed for 2.5 - 5 years. Human breast milk contains every nutrient a baby needs for several years after birth.
And human breast milk does contain lactose. As babies, we manufacture an enzyme called lactase which helps to digest lactose. Once we are weaned, however, our bodies stop producing lactase. We effectively become lactose intolerant. Because after weaning, we would never again encounter milk, and never again need the ability to digest lactose.
Even today, an average of 70% of the world’s population can not adequately digest lactose. This condition can range from discomfort during digestion to full blown allergy. It also varies greatly by race, with Asians topping the charts at approximately 90% and Caucasians at the other end of the spectrum hovering around 40 - 50%. Around 80% of black people and Native Americans are maldigesters of lactose.
And evolutionarily, this makes sense. Why would we need the ability to digest lactose after weaning? Before the agricultural revolution 11,000 years ago, humans did not drink milk past the age of weaning, and never drank the milk of other mammals. Modern humans are the only animal on earth that chooses to drink milk in adulthood, and the only animal on earth that drinks another mammal’s milk.
We are maladapted to consuming milk. Our bodies are not designed to drink milk in adulthood, and certainly not designed to drink the milk of other species.
Conclusion
Humans do not have any specialized adaptations to eating meat, dairy, or eggs. By contrast, humans have many specialized adaptations to consuming plants. Humans display all the anatomical markers of plant eaters, and cooked starches are what have allowed humans to grow a big brain. The fossil record has historically and incorrectly been skewed towards the conclusion that early humans ate a meat-heavy diet, but more recent research suggests that the vast majority of early human diets were composed of plants.
Yes, early humans did kill and eat some animals. But meat consumption - and certainly dairy and egg consumption - did not play a large enough role in our evolution to shape our anatomy or physiology.
Our bodies are designed to eat plants.
Veganism is not only the best choice for ethical and environmental reasons, it is also the diet that is best suited to our bodies.
Veganism isn’t for “extremists.” Veganism is for everyone!