By Dr. Becker
According to the journal Nature:
"Carnivores have experienced stronger natural selection than plant-eating animals, perhaps because of their limited diet."1
Natural selection is the process by which organisms adapt to their environment, allowing them to survive and produce offspring.
The journal cites a recently published Korean study that looked at the evolution of "carnivory" (meat-eating) by comparing the genomes of mammals across three dietary groups: carnivores (leopards), omnivores (humans) and herbivores (giant pandas).2
The researchers discovered that carnivores have lost a number of genes involved in carbohydrate digestion. In addition, they share changes across species to genes involved in muscle strength and agility that support their hunting skills.
Omnivores and herbivores, on the other hand, share fewer evolutionary adaptations with others in their groups, which suggests their diets "… have imposed weaker selection compared with that of carnivores," according to Nature.
The researchers also observed that big cats have experienced recent losses in genetic diversity, "… which may be due to the inflexible nature of their strict diet, highlighting their vulnerability and critical conservation status."3
In other words, the diet of cats exerts a uniquely powerful influence on their DNA that has the potential to put them at risk of extinction.
Previous Study: Housecats Are 95 Percent Tiger
Three years ago, a research team that included some of the same scientists involved in the above study sequenced the genomes of tigers, lions and snow leopards as part of conservation efforts to save wild cats from extinction.4
Habitat loss, poaching and shrinking food supplies have put tigers near the top of the world's most endangered species list. There are thought to be only a few thousand remaining in the wild.
For the study, the researchers sequenced the whole genome of a 9-year-old Amur tiger, also known as the Siberian tiger, and compared it to the genomes of a white Bengal tiger, an African lion, a white African lion and a snow leopard. The sequencing provided several fascinating insights, for example:
✓ In big cats, several genes are altered in the metabolic pathways linked to protein digestion and metabolism. Those adaptations, which evolved over tens of millions of years, are thought to be what allows felines, as obligate carnivores, to digest and live solely on a diet of animal meat.
✓ Big cats also have a number of gene mutations that explain their incredibly powerful, fast-acting muscles.
✓ The snow leopard had unique amino acid changes in certain genes that may contribute to its ability to adapt to high altitudes.
✓ The genes associated with muscle strength, energy metabolism and sensory nerves — including those involved in visual acuity and sense of smell — seem to be undergoing rapid evolution in the tiger.
✓ White lions possess a variant in the TYR gene, which is the gene related with white coat color in domestic cats, as well as a form of albinism in humans.
✓ Siberian tigers share 95.6 percent of their DNA with housecats
Your Cat Fluffy, the Meat-Eater
Cats are obligate carnivores, also called hypercarnivores or true carnivores, defined as follows:
"An obligate carnivore (or true carnivore) is an animal that must eat meat in order to thrive (Syufy 2008). They may eat other foods, such as fruits, honey, grains and so forth, but meat must be included in their diet.
True carnivores lack the physiology required for the efficient digestion of vegetable matter, and, in fact, some carnivorous mammals eat vegetation specifically as an emetic.
The domestic cat is a prime example of an obligate carnivore, as are all of the other felids (Pierson 2008)."5
Cats must eat animal meat and organs to meet their nutritional needs, and plant-based proteins (grains and vegetables) are no substitute.
Kitties lack the specific enzymes necessary to use plant proteins as efficiently as animal proteins. The proteins derived from animal tissue contain a complete amino acid profile. Amino acids are the building blocks of protein.
Plant-based proteins don't contain all the amino acids critical for the health of an obligate carnivore.
Humans, who are omnivores, have the physiological ability to turn plant proteins into the missing pieces needed for a complete amino acid profile. To a very limited extent dogs can do this as well, but a cat's body isn't equipped for it whatsoever.
Why Fluffy Needs so Much Animal Meat
Cats also need much more protein in their diet than other animals. Kittens require 1.5 times more protein than puppies. Adult cats need two to three times the amount adult dogs require.
This is because while other mammal species use most of the protein they consume for growth and body maintenance, cats use it for those purposes and also as a source of energy.
When other species are fed a low-protein diet, their bodies make adjustments to conserve amino acids to manage the deficit. But a cat's body must continue to use protein even when there's not enough in the diet, which is why protein malnutrition is common in sick, injured and anorexic kitties.
In addition to their increased need for protein, cats also have a higher requirement for certain specific amino acids found naturally in animal tissue.
One of the amino acids missing in plants is taurine, which is found in animal muscle meat, in particular the heart and liver. Taurine deficiency causes serious health problems in cats, including cardiovascular disease and blindness.
Cats Also Have Distinct Dietary Vitamin Requirements
Felines have a special requirement for vitamin A, which is available naturally only in animal tissue. They lack the intestinal enzymes necessary to convert beta-carotene in plants to the active form of vitamin A, which is essential for vision, bone and muscle growth, reproduction and the health of epithelial tissues.
Cats also require five times more dietary thiamine (vitamin B1) than dogs. A thiamine deficiency can result in a poor-quality coat, loss of appetite, hunched posture, neurologic problems including seizures and even death.
Since vitamin B1 isn't stable in commercial pet foods and levels drop significantly the longer the food is stored (pet food formulator Steve Brown's research shows it's gone after three months), many cats may be thiamine-deficient unless they're eating a freshly made real food diet or are receiving a supplement. The issue is most B vitamins come from China.
Cats must consume vitamin D in their diet because they can't synthesize it through their skin. The liver and fatty tissues of prey animals are rich in vitamin D. Kitties must also get arachidonic acid, an omega-6 fatty acid, from their diet.
Last but Not Least, Fluffy Needs a Moisture-Rich Diet
One more distinctive biological feature of cats is their need to get most of their water intake from the food they eat, because they're not as responsive as other animals to sensations of thirst or dehydration. Unlike dogs, who drink frequently from their water bowls, cats fed a dry diet aren't compelled to search for another source of water to make up the difference between what their bodies require and their diet provides.
This can result in chronic mild dehydration, a condition that will ultimately result in disease, especially of the lower urinary tract and kidneys.