Similarities between humans and many different animals are often cherry-picked to argue that humans are natural herbivores or omnivores. As true herbivores, cows provide a model against which to compare human physiology and nutritional needs. And comparing our diets and bodily functions to those of cows, it is clear that they are stricter herbivores than us. So, the debate over the optimal human diet is less about whether we can eat animal-based foods than whether we should.
Similarities between humans and many different animals are often
cherry-picked to argue that humans are natural herbivores or omnivores. As true
herbivores, cows provide a model against which to compare human physiology and
nutritional needs. And comparing our diets and bodily functions to those of
cows, it is clear that they are stricter herbivores than us.
So, the debate over the optimal human diet is less about whether we can eat
animal-based foods than whether we should. Additionally, comparing ourselves to
cows raises the question: are animal dairy products a natural part of the human
diet?
Shared genes between species
All creatures, regardless of their diets, share some genetic similarities.
Shared genes are usually associated with functions common to all animal groups.
It’s not surprising, then, that we share about 80% of our genes with domestic
cows.[1] We’re also about 60% similar to chickens and share 85% of our
protein-encoding genes with mice.[2]
Within the human species, we’re all 99.9% genetically identical to each
other.[3] Even tiny differences in genetics can result in a wide range of traits
among humans, which suggests that shared genes among animals is a function of
how nature works rather than an indication of meaningful similarity.
Digestion in the ruminant stomach
Cow stomachs vividly illustrate our differences. As ruminants, cows have a
four-chamber stomach designed to break down parts of plants that humans, with
our single-chamber stomachs, can’t.
Each chamber in the ruminant stomach has a distinct function:[4]
In humans, plant fibers remain undigested. When they pass into the colon,
gut microbiomes break them down to produce byproducts like vitamins and
short-chain fatty acids.[6] But since we lack the cellulase enzyme, we
cannot digest many of the fibers that break down easily in cows’ stomachs.
Protein and human digestion
Our stomachs are designed mainly to digest protein. When food enters the
stomach:[7]
Barring any allergies or intolerances, the process works equally well for
animal and plant proteins.
Cows, on the other hand, get their protein from their ruminant microbes.
These microbes can extract nitrogen from sources like grass and use it to
make protein. When microbes die, they also get broken down as additional
protein sources.[8] This process allows cows to extract more protein from a
low-protein diet than humans can.[9]
Proteins that can’t break down in the rumen are called rumen undegradable
proteins, or bypass proteins. They pass into the abomasum and small
intestine for digestion and absorption. Animal-based proteins are a form of
bypass protein; they can disrupt cows’ microbiomes, leading to digestive
distress or even death.[10]
What cows can (and can’t) teach us about human diets
Despite genetic similarities, cows and humans have vastly different dietary
requirements. Our digestive systems don’t fully digest some of the plant
matter from which cows derive most of their nutrition, and we can’t rely on
our microbiomes as a main source of amino acids.
Because we can get those amino acids—and the other nutrients we need—from
various sources, we have greater dietary flexibility than cows. This is the
classic definition of an omnivore.[11]
It bears repeating: the debate over the optimal diet is less about whether
we can eat animal-based foods than whether we should. Science shows that we
can not only survive but also thrive on exclusively plant-based diets and
that a diet consisting predominantly or entirely of whole plant foods tends
to be the best choice for long-term health.
Given all the differences between humans and cows, you might also wonder:
why do we insist on getting calories from cow’s milk and its derivatives? In
newborn mammalian species, the lactase enzyme is responsible for helping
break down lactose, with the expression of this enzyme declining after
weaning.[12] Essentially, weaned mammals—adult mammals—grow out of this need
to break down the carbohydrate in their mother’s breast milk.
Humans are the major exception: through evolutionary processes that
researchers are still trying to understand better, about one-third of humans
have developed lactase persistence. This development is often linked to
“changes in food production practices during the Neolithic revolution,” when
certain populations began domesticating animals and consuming more of their
milk. Even still, that means the majority is not well-suited to consume
lactose, not even the lactose of their own species (much less the lactose
found in the milk of other species!).
References
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We began this archive as a means of assisting our visitors in answering many of their health and diet questions, and in encouraging them to take a pro-active part in their own health. We believe the articles and information contained herein are true, but are not presenting them as advice. We, personally, have found that a whole food vegan diet has helped our own health, and simply wish to share with others the things we have found. Each of us must make our own decisions, for it's our own body. If you have a health problem, see your own physician.