THE ANATOMY OF EATING
As a faithful companion to
humans for some 10,000 years, the trend to
humanize our companion dogs comes as no
surprise. Yet despite his long and close
association with humans, the dog remains closest
genetically to the gray wolf, with whom he
shares over 99% of his mitochondrial DNA. The
close genetic relationship between dog and wolf
led the Smithsonian Institution to reclassify
the dog from its previous separate species
designation of Canis familiaris to Canis lupus
familiaris. In other words, the Timber wolf, the
Tundra wolf, and our beloved companion dog, all
fall under the genetic umbrella of the gray
wolf: Canis lupus. Just like wolves, all dogs
are evolved as carnivores, with anatomical
features that clearly adapt them for meat-based
diets. Understanding the anatomical differences
between carnivores, omnivores and herbivores
helps understand why dogs and cats are
classified as carnivores, and what foods best
match their anatomy.
THE ANATOMICAL DIFFERENCES OF HERBIVORES,
OMNIVORES & CARNIVORES
To understand the nutritional needs of dogs and
cats, it is useful to begin with a basic
understanding of their anatomical features, and
how they differ from herbivores and
omnivores. By understanding which anatomical
features are associated with each kind of diet,
we are able to classify an animal as:
CARNIVORE (meat eaters),
HERBIVORE (plant-eaters), or
OMNIVORE (both meat and plant eaters)
This classification helps us understand which
foods the animal is actually adapted to eat.
HERBIVORES (cows, sheep)
Herbivores eat plants, not meat. So it’s no
surprise that their anatomical features are
adapted to process carbohydrates and other
nutrients produced by plants.
Anatomical features common to herbivores
confirm their adaptation for a plant-based diet.
LONG DIGESTIVE TRACTS up to 10 times their body
length are needed due to the relative difficulty
with which plant foods are broken down.
Herbivores have significantly longer and much
more elaborate guts than do carnivores.
SQUARE FLAT MOLARS provide an ideal grinding
surface to crush and grind plants (but not
meats). A lower jaw with a pronounced sideways
motion facilitates the grinding motion needed to
CARBOHYDRATE-DIGESTING ENZYMES IN SALIVA.
AMYLASE is a digestive enzyme in saliva that
helps in digesting carbohydrates. Herbivores
methodically chew their food to ensure the
thorough mixing with amylase.
OMNIVORES (pigs, bears, humans)
Omnivores (from Latin: omne all, everything;
vorare to devour) are evolved to eat both plants
and animals.As general feeders, omnivores are
not specifically adapted to eat meat or plant
Anatomical features common
to omnivores include:
MEDIUM LENGTH DIGESTIVE TRACTS that provide the
flexibility to digest both vegetation and animal
FLAT MOLARS AND SHARP TEETH developed for some
grinding and some tearing.
SALIVA CONTAINS CARBOHYDRATE DIGESTING ENZYME
AMYLASE which is responsible for the majority of
CARNIVORES (wolves, dogs, cats)
Carnivore means 'meat eater' (Latin carne
meaning 'flesh' and vorare meaning 'to devour')
and classifies animals whose diets consist
mainly of meat – such as dogs and cats.
The anatomical features of carnivores
SHORT, SIMPLE & ACIDIC DIGESTIVE TRACTS. Protein
and fat from animal source are quickly and
easily digested – hence the short digestive
system of dogs and cats. The ability of dogs and
cats to secrete hydrochloric acid is also
exceptional. To facilitate protein breakdown and
kill the bacteria found in decaying meats, dogs
and cats are able to keep their gastric pH
SHARP TEETH (designed for slicing meat, not
grinding plants). Carnivores have elongated
teeth designed for tearing and killing prey.
Their molars are triangular with jagged edges
that function like serrated-edged blades that
give a smooth cutting motion like the blades on
a pair of shears.
JAWS MOVE VERTICALLY unlike herbivores and
omnivores that grind their food by side to side
chewing, the jaws of dogs and cats operate
vertically to provide a smooth cutting motion,
and open widely to swallow large chunks of meat.
NO AMYLASE IN SALIVA. Amylase in saliva is
something omnivorous and herbivorous animals
possess, but not carnivorous animals like dogs
or cats. As amylase is not present in saliva,
the burden is entirely on the pancreas to
produce the amylase needed to digest
carbohydrates. Feeding dogs as though they were
omnivores or herbivores makes the pancreas work
harder in order to digest the
carbohydrate-filled foods (instead of just
producing normal amounts of the enzymes needed
to digest proteins and fats).
CONCLUSIONS | CATS & DOGS ARE DESIGNED FOR AN
ALMOST EXCLUSIVELY MEAT-BASED DIET
Several key anatomical features separate dogs
and cats from omnivores and herbivores, while
clearly classifying them as carnivores with an
adaptation for an almost exclusively meat based
STOMACH TYPE & LENGTH
Dogs & cats posses a short, simple
gastro-intestinal tract. Because meat is easily
digested (relative to plants) their small
intestines are short. A high concentration of
stomach acid helps quickly break down proteins
(Carnivores have a stomach acidity of about pH 1
-compared to humans at pH 4 to 5).
TEETH & JAWS
A large mouth opening with a single hinge joint
adapted for swallowing whole chunks of meat.
Short and pointed teeth designed for grasping,
ripping and shredding meat (not grinding
Teeth and jaws designed to swallow food whole
(not for chewing or crushing plants).
Adapted to break down protein and fat from meat
(not plants or grains), the saliva of dogs and
cats does not contain the digestive enzyme
amylase. Carnivores don’t chew their food.
Unlike carbohydrate-digesting enzymes,
protein-digesting enzymes cannot be released in
the mouth due to the potential of damaging the
oral cavity (auto digestion). Therefore,
carnivores do not mix their food with
saliva—they simply bite off huge chunks of meat
and swallow them whole.
THE DIETARY NEEDS OF DOGS AND CATS
The dog is, by all scientific standards and by
evolutionary history, a domesticated wolf. This
raises the question of which foods are
appropriate for their carnivorous anatomy, and
which are not?
As the dog's internal physiology does not differ
from the wolf, dogs have the same physiological
and nutritional needs as their wild predator
cousins, whose diets are almost exclusively
proteins and fats. Modern dogs of all breeds
are not only capable of eating the food of their
wild ancestors, but actually require it for
maximum health. This is because their basic
physiology has changed very little with
domestication—despite the obvious differences in
their physical appearances.
ANIMAL SOURCE PROTEINS
Protein is the staff of life for dogs and cats –
essential to basic body functions, including
cellular regeneration, tissue maintenance,
hormone and enzyme production, and the provision
of energy. Although protein is essential, not
all proteins function equally, with protein
qualities varying enormously between various
Three factors affecting protein quality
AMINO ACID COMPOSITION
Due to the different amino acid profiles
contained in animal and plant proteins, ANIMAL
PROTEINS are considered ‘complete proteins’ for
dogs and cats, while PLANT PROTEINS are
considered ‘incomplete proteins’.
AMINO ACID COMPOSITION
ANIMAL PROTEINS contain all of the amino acids
essential to dogs and cats in quantities that
match the requirements needed for their overall
health, maintenance and growth.
PLANT PROTEINS such as corn gluten, soybean meal
or plant protein isolates, do not contain all of
the amino acids in the right proportions that a
dog or cat needs. Amino acids essential to dogs
and cats often missing in plant proteins,
include arginine, taurine, methionine, lysine
Protein digestibility is a key quality
measure. After all, what good is it to have a
food made with a higher quality protein if it’s
not also easy to digest? A food with high
protein digestibility is one that can be broken
down into smaller easy-to-absorb components
easier and quicker than others. In the short
digestive systems of dogs and cats, plant
proteins are far less digestible than meat
proteins. Animal source protein is the best
choice -it is easily digested and contains the
amino acids essential for dogs and cats.
ANIMAL SOURCE FATS
While often viewed negatively by health
conscious people, fat is an essential dietary
requirement for dogs and cats.As many people are
concerned with reducing our fat intake, we often
fail to realize the essential role that fat
plays in the diets of our dogs and cats.
Just as with protein, fats are also not created
equally and differ greatly in their component
structure and quality.Dogs and cats don’t suffer
from cholesterol problems or heart disease
caused by higher levels of animal fats, and it
comes as no surprise that cats and dogs need fat
from animals, rather than plant source.
Two key roles of dietary fat are:
1. Providing a concentrated source of energy.
2. Supplying the Essential Fatty Acids (Omega-3,
for example) that dogs and cats cannot produce
within their own body.
FAT AS ENERGY
Both dogs and cats require a fairly high amount
of animal fat in their diets. As companion dogs
and cats enjoy a more sedentary lifestyle than
their wolf relatives, moderation of fat is
important, with an optimum range of 15-18% fat.
While both fats and carbohydrates provide
energy, they function very differently in the
body of a dog or cat. Fats are essential in the
diets of dogs and cats, carbohydrates are not.
Carbohydrates provide energy more rapidly
compared to fats. In humans, a high intake of
carbohydrates increases muscle-glycogen, which
increases stamina. The same carbohydrate loading
in dogs creates an excess accumulation of lactic
acid in the muscles, leading to a condition
called hypoglycemia, which causes weakness and
fatigue. Animal fats are clearly the choice of
energy for dogs and cats.
ESSENTIAL FATTY ACID SUPPLY
Essential fatty acids are the fatty acids
present in fats that are required by
the body. Because they cannot be produced in the
body, Essential Fatty Acids must come from
foods. The most important are linoleic and
arachidonic4 (Omega-6), and DHA and EPA
(Omega-3). An appropriate balance of omega-6 and
omega3 is important as these two fats work
together. A ratio of 2:1 to 5:1 is generally
accepted as ideal for dogs and cats. A lack of
Omega-6 is extremely rare, most pet foods have
too much Omega-6 and not enough Omega-3.
Omega-3 quality varies dramatically between
plant and animal sources. Of the 3 kinds of
Omega-3: ALA (alphalinolenic acid) is from
plants, while DHA (docosahexaenoic acid) and EPA
(epicosapentaenoic acid) are from fish.
Dogs and cats require DHA and EPA, not ALA.
Plant source Omega-3 is ALA, a short-chain
omega-3 found in soy, canola oil and flax. ALA
must be converted to EPA and DHA to be of any
nutritional benefit to a dog or cat. As cats and
dogs are not adapted to create this conversion,
ALA Omega-3 from plants is considered ‘inactive’
and not Biologically Appropriate for dogs and
cats. While dogs are able to produce arachidonic
acid from linoleic acid, cats cannot synthesize
arachidonic acid and require it in their diet.
EPA & DHA
Omega-3 from fish: Animal Omega-3s (EPA and DHA)
are long-chain omega-3s that are absorbed
readily and directly within the body. Naturally
present in oily fish such as salmon, herring and
lake whitefish, EPA & DHA and are by far the
best Omega-3 choice for dogs and cats.
CARBOHYDRATES – AS FEW AS POSSIBLE
Carbohydrates are usually the first source of
energy available to the body. Proteins and fats
also provide energy but carbohydrates are
called upon first. According to the NRC
guidelines, “Carbohydrates provide an economical
source of energy in the diet of dogs.”
Carbohydrates are divided into two broad
1). SIMPLE CARBOHYDRATES or sugars, and
2). COMPLEX CARBOHYDRATES.
Simple carbohydrates are made up of single
sugars, or two sugars joined together and are
found in grains such as corn, wheat and rice.
Simple sugars are quickly absorbed into the
blood stream, causing a rapid rise in blood
sugar levels. This rapid rise causes the body to
produce a sharp rise in insulin levels and
results in the sugars being converted into fat.
The rapid rise in blood sugar levels is usually
followed by a rapid drop, leading to feelings of
hunger and weakness.
Complex carbohydrates have more than two units
of sugar joined together and are found in
potatoes, beans, as well as many other
vegetables and fruits. Complex carbohydrates
can take a long time to break down in the
stomach or pass through undigested, creating
ARE CARBOHYDRATES APPOPRIATE FOR CARNIVORES?
Dogs and cats have no nutritional need for
carbohydrates and are evolved to use protein and
fat as energy sources.
The natural diet
contains almost no carbohydrate at all, and
the small predigested grains, fruits &
vegetables in the stomach of a prey animal
make up a very small fraction of the total
Today’s high carbohydrate pet foods lead to
blood sugar fluctuations, insulin resistance,
and are widely considered as a leading cause
of obesity, diabetes and a host of other
health problems in cats and dogs.
Conventional dry dog foods have a very high
carbohydrate content, with most foods
exceeding 40-50% in total carbohydrate
Almost half of typical dry dog foods is
nonessential, simple sugars! This important
fact is often lost on consumers as pet food
makers are not required to claim carbohydrate
content on their packages.
Carbohydrate intake above the daily needs of
the dog (which regularly occurs with
conventional pet foods) prompts internal
enzyme factors to store the extra carbohydrate
as body fat.
The Association of American Feed Control
Officials’ (AAFCO) nutrient profiles show that
carbohydrates are not essential for dogs and
cats, and that no minimum level of
carbohydrate is needed in their
diets. According to Dr. David S. Kronfeld,
carbohydrates need not be supplied to adult
dogs, even those working hard as the liver is
easily able to synthesize sufficient glucose
(from protein and fats).
FEEDING CATS & DOGS
ACCORDING TO THEIR ANATOMY
Cats and dogs evolved as hunters and despite a
modern lifestyle, their digestive systems and
internal anatomical features have remained
unchanged for hundreds of years. Despite obvious
and dramatic changes in their physical
appearance, the basic physiology of the modern
dog has changed very little with domestication.
Today’s modern dogs are not only capable of
eating the food of their wild ancestors, but
actually require it for maximum health. A
biologically appropriate diet mirrors the same
balance and variety of ingredients that would be
consumed in the wild, including muscle meat,
bone, fat, organ meat and vegetable materials.
Applied to dry foods, the Biologically
Appropriate concept means higher-protein,
moderate fat, low carbohydrate foods that
contain high and various inclusions of animal
ingredients that are processed as little as
possible. Cereal grains are excluded and
carbohydrates are reduced.
Despite obvious changes in their physical
appearance, the basic physiology of the modern
dog and cat has changed very little with
domestication. Conclusions are that dogs and
cats are evolved as carnivores, and that despite
obvious differences in appearance from their
wild cousins, their internal anatomy remains
Dogs are carnivores, not omnivores. Dogs ARE
very adaptable, but just because they can
survive on an omnivorous diet, does not mean it
is the best diet for them.
With short digestive
tracts and gastrointestinal systems, dogs and
cats are adapted to metabolize animal flesh
and fat, not grains and carbohydrates.
Today’s modern dogs (of any breed) are not
only capable of eating the food of their wild
ancestors, but actually require it for maximum
Biologically Appropriate foods are designed
to match the digestive capability of dogs and
cats. Just like the natural diet, they are
high in protein and low in carbohydrates, with
a concentration and variety of minimally
processed meats and fats from animal source.
Although these findings
are well accepted within the scientific
community, conventional dry dog and cat foods
appear to be created on the premise that the
digestive system of the dog and cat is similar
to humans - with a heavy emphasis on
inappropriate grains and carbohydrates.