For our third installment in this month’s One Health series, we are going to broach the subject of how humans (as omnivores) differ from other animals on this planet who are true herbivores. I feel it is very important to set the record straight on this topic.
When it comes to eating, I hear a lot of talk comparing humans with other animals. For example, some argue that cows are ‘vegan’ because they eat plants all day and don’t need animal protein to be healthy so ‘logically’ we humans should be able to do the same.
But there’s a huge problem with this line of thinking…
For starters, a human is not a two-legged cow.
Nor is a plant-based diet the equivalent of grazing on grass.
Just because both species eat plants does not at all mean that a cow’s diet is good for us and vice versa.
Our physiology does not resemble a cow’s and, therefore, we don’t gain nutrition in the same way.
In fact it is important to point out that every animal is different; we simply can’t compare ourselves to other animals—especially true herbivores.
At the end of the day, comparing human’s nutritional requirements to the needs of a true herbivore may well be counterproductive to a constructive dialogue and thorough understanding of a plant-based diet.
Let’s explore this subject together in detail…
Let’s Look at the Definitions…
Let’s first start by defining the differences between omnivores and herbivores.
Omnivores are animals that are not specialized eaters — that is they acquire and process food from a number
of food sources including animals and plants, algae and fungi. They’re also known as ‘general’ or opportunistic feeders.
For example, an omnivore like a wolf evolved with a preference for meat, but as an opportunistic feeder, also eats grasses, vegetables, and even fruit. In the absence of meat, a wolf can survive on nothing but plant matter.
Some examples of omnivorous animals are (most) bears, badgers, raccoons, opossums, and pigs. And humans of course!
Herbivores do specialize eating plants as the main component of their diet. They are adapted to eating this way with mouths that ‘rasp’ or ‘grind’ tough plant material like tree bark and grasses. Horses, for example, have wide, flat teeth perfectly suited for grazing on grasses.
Herbivores are further divided into grazers (cows, for example) who clip vegetation at or near ground level or browsers (giraffe, for example) who eat mostly leaves, twigs and green stem from plants.
(Humans are neither of these. We don’t have the teeth or the digestive system for it.)
Herbivores include gorillas, cows, horses, elephants, rhinos and giraffes. There are many more, but for our purposes, we’re going to use this set of herbivores to discover how humans are dissimilar to the herbivores.
The Difference Lies in the Digestion…
The human digestive process–and the way we absorb nutrients–make us diametrically opposed to a true herbivore. In fact, comparing the two is like comparing an apple to an orange.
Let me explain…
Humans are omnivores and monogastrics (we have one stomach). Digestion is primarily enzymatic, which simply means that we employ enzymes to break down food into simple compounds that can then be either absorbed as nutrients or eliminated from the body.
Herbivores can be monogastrics or ruminants, which have a complex four-chambered stomach. Herbivores digest cellulose — which makes up most of a plant’s cell walls — from plant matter via fermentation. Herbivores need microbes to ferment plant matter, and their nutrients come from that process of microbial fermentation.
There are two types of fermenters: foregut and hindgut. They all digest cellulose with the help of their gut microbiota, but it happens in different parts of the digestive system. Because of this, the plants they eat will be necessarily different from each other to obtain the nutrients they need.
When humans eat cellulose, it can’t be broken down by enzymes. Only a small part of the cellulose will be broken down by our gut microbes in the large intestine.
The small quantity of cellulose we do eat is important to our health because it contains much-needed insoluble fiber, which helps move things along in our digestive systems. However the fact remains that most of our nutrients still come from enzymatic digestion.
Simply put, humans don’t digest like cows. And if we were to eat ‘like a cow’ (i.e. only grasses), it would be virtually impossible to get all the nutrients we need.
Ruminating About Rumination
Ruminants (e.g. cows, deer, goats, antelope, bison, buffalo, moose, giraffe, elk) have a specialized stomach for fermentation, which requires that they chew, regurgitate and chew their food (cud) again. We humans don’t do this (thankfully!).
(By the way, our digestive differences start in the mouth. Most ruminants have a thick dental pad they use to chew plant-based foods and they don’t have upper incisors.)
The ruminant has a stomach that is made up of four separate compartments, each with its own digestive function. After bacteria have done the job of fermenting cellulose, ruminants digest those bacteria in the fourth stomach chamber — the only enzymatic digestive chamber in their complex four-stomach system.
Unlike humans, ruminants do not absorb glucose from dietary carbohydrates via an enzymatic process. Instead, they get their energy from Volatile Fatty Acids (VFAs) through fermentation of fibrous and non-fibrous carbohydrates in the first two chambers and obtain the majority of their protein from the digested bacteria (i.e. microbial protein) in the fourth chamber of their stomach.
Ruminants are foregut fermenters because their digestion occurs in the foregut, i.e. before the small intestine. Other grazing animals are monogastric and hindgut fermenters because microbial fermentation takes place in digestive organs that follow the small intestine (colon and cecum).
Horses and rhinos, small rodents and rabbits are hindgut fermenters. They tend to have large, complex intestines about 10-13 times the length of their bodies. Hard-to-digest compounds such as fiber make this long gastrointestinal tract necessary and also allow them to eat small amounts of forage all day long.
Monogastric herbivores can survive in conditions where ruminants wouldn’t be able to get the nutrition they need because they can extract more nutrition from smaller quantities of food.
Whether the herbivore is a ruminant foregut fermenter or a monogastric hindgut fermenter, their digestive systems’ structure and eating requirements resemble nothing like ours.
What About Elephants and Gorillas?
Other so-called ‘vegans’ like elephants and gorillas eat a mostly vegetarian diet and they’re often held up as an example of what the human diet can be. These are beautiful, powerful animals and it’s tempting to use them as symbols of plant-eating strength but they bear little resemblance to us when it comes to eating or digesting.
Let’s take a closer look.
Elephants eat about 375 pounds of vegetation every day including twigs and tree bark, small bushes and roots, grasses and fruits. Tree bark is a staple in the elephant’s diet because it aids in digestion.
Gorillas eat about 40 pounds a day and they are more selective in their foraging. They eat only particular parts of the plants they consume. They might eat only the root, the leaves or the stock of a given plant. Most of the gorilla’s diet is ‘plant-based’, but depending on the subspecies, they might also consume a small percentage of insects, grubs, and snails.
While gorillas are a close cousin of humans with 98.25% genetic similarity, we have different physiology — from the anatomy of our brains to the complexity our digestive systems.
The Big Belly Factor
For example, a big-bellied gorilla is considered healthy while a big belly on a human signals obesity — with all its associated health problems. For gorillas, that big belly is necessary because the size of their colon is both longer and larger than humans so they can ferment the plant fibers they eat and accommodate all the bacteria needed for the fermentation process.
Human (whole food) plant-based eaters rarely have a big belly. Because humans rely on starches and intact sugars that are broken down through enzymatic digestion, a plant-based eating human tends to be thin, muscular and healthy.
It once again simply doesn’t make sense to think that our nutritional requirements are similar to those of big-bellied fermenters in the wild.
The Most Important Difference of All
But maybe the most important thing to note when we’re discussing a plant-based human vs. a herbivore in the wild is the sheer time and energy it takes a true herbivore to survive every day.
For example, did you know that an elephant spends nearly 80% of its day (16-18 hours) just eating?
In fact, they spend most of their waking life in search of food!
If humans were true herbivores, we wouldn’t have time for anything but eating and sleeping. But because we can digest starches through an enzymatic process and store the energy we get from them, we are freed from the endless cycle of eating.
This alone separates humans and other omnivores from all true herbivores.
Different species have different digestive systems, physiology, and nutritional requirements.
So while a plant-based diet is absolutely the most healthful choice for humans, we still can’t compare our plant-based eating with that of a cow, gorilla or elephant.
We can be happy and healthy eating a plant-based diet, but that does not make us herbivores. What is good for them is not necessarily what we need. Science tells us as much.