By Dr. Becker
A study1 was published in October 2011 on the digestibility of three different feline diets -- a raw beef-based diet, a cooked beef-based diet, and a high-protein extruded (dry food/kibble) diet.
The study involved 9 shorthair domestic cats, adult females.
The result? The protein in both raw meat and cooked meat diets is better digested by cats than the protein in the kibble.
Although the kibble started out higher in protein, the protein in the real meat provided better nutrition for the kitties.
According to study authors:
Our results indicated that cooking a raw meat diet does not alter apparent total tract energy and macronutrient digestibility, and may also minimize risk of microbial contamination.
Given the increasing popularity of feeding raw diets and the metabolic differences noted in this experiment, further research focused on the adequacy and safety of raw beef-based diets in domestic cats is justified.
I suspect, based on the fact that a pet food company was affiliated with this study, the purpose of the research was actually to look at the difference in the protein digestibility of cooked meat vs. raw meat -- since it's a well-established fact kibble doesn't provide the same high quality nutrition for obligate carnivores that real meat does.
According to retired holistic vet Dr. Jean Hofve (who also founded Spirit Essences2 and co-wrote The Complete Guide to Holistic Cat Care: An Illustrated Handbook3), a major pet food manufacturer conducted similar research many years ago, with the same result. Nothing was ever published from that study.
Per Dr. Jean:
"... one of these days, the big pet food companies will introduce their own raw products. I believe the major companies already have the plans, and are simply waiting for the right time--and that time is the instant they think they can make a profit on raw meat diets."
Past Studies on Protein Digestibility in Felines
November-December 2010. A study of nutrient digestibility and nitrogen metabolism of raw vs. extruded diets on African wildcats, published in Zoo Biology4:
Protein digestibility was higher (P<0.05) when cats were fed the raw meat diet vs. the kibble diet.
April 2009. A study of the macronutrient digestibility of four raw meat diets in domestic cats, published in the journal of The Federation of American Societies for Experimental Biology (FASEB)5:
Although dietary macronutrient composition was highly variable and statistical differences were noted, all diets were highly digestible.
January 2008. A study of the nutrient digestibility of a raw, beef-based diet in captive exotic felines, published in Zoo Biology6:
The beef-based raw diet was highly digestible; however, differences in fat and digestible energy suggest that species should be considered when determining caloric needs of exotic felids.
March 1997. A study comparing raw meat-based and dry kibble diets in sand cats, published in the Journal of Animal Science7:
The kibble and raw meat-based diet met or exceeded the requirements of domestic felids (NRC, 1986; Dzanis, 1994). However, the raw meat-based diet was almost 15% more digestible than the kibble diet. This may be due to the constituents of the diet.
Felid species are considered strict carnivores (Czarnecki, 1983), and they utilize little, if any, fiber (Maskell and Johnson, 1993). Thus, they may be able to digest and absorb nutrients more readily from a raw meat-based diet than from a kibble diet, which contains a considerable amount of plant matter (McDonald et al., 1981). Indeed, digestibilities for dogs consuming animal matter (i.e., lung, tripe, or minced meat) were greater than those for dogs consuming a soy-based diet (Neirinck et al., 1991).
Our results indicate that kibble diets may not be as digestible as raw meat-based diets fed to small exotic cats. This difference in digestibility has important implications for required food consumption.
Why Your Cat Needs Highly Digestible Protein
Felines have a unique nutritional biochemistry that is significantly different from other animals. As obligate carnivores, they must consume nutrients in animal tissue to meet their very specific nutritional requirements.
Cats have minimal need for carbohydrates, and while they can use some carbs as a source of metabolic energy, those nutrients can't compensate for a lack of protein.
When it comes to protein, kittens require 1.5 times the amount as the young of other species. Adult cats need 2 to 3 times the amount of protein other adult animals require.
Omnivores and other mammals use most of the protein they consume not as a source of energy, but for growth and body maintenance. Cats use protein for those purposes, and also as a source of energy.
When most animals 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 happens quickly in sick or injured cats, and cats suffering from anorexia.
In addition to their increased need for protein, cats also have a higher requirement for certain specific amino acids found naturally in animal tissue.
Why Your Cat Won't Thrive on a Carbohydrate-Rich Diet
Cats' bodies aren't equipped to digest carbohydrates efficiently. They lack the salivary, intestinal and pancreatic enzyme activity necessary to break down and digest carbs.
Since domestic cats evolved to eat very low amounts of grains, common sense tells us a diet high in carbohydrates might create ill health.
A high-carb diet decreases protein digestibility. It also causes an increase in microbial fermentation in the large intestine and production of organic acids.
Feline liver enzymes also function differently from those of most other animals. They do not upregulate to handle large amounts of carbohydrates in the diet. The activity of a cat's liver enzymes is designed to handle protein and fat as energy sources, not starches. The majority of carbs in a cat's diet are ultimately stored as fat.
The livers of cats also do not produce the enzyme necessary to metabolize simple sugars. Research shows that cats fed diets high in simple sugars become hyperglycemic. Most cats aren't attracted to sweet-tasting foods (unlike dogs and people), and instead prefer food that tastes like animal products. This is another clear indicator of the strict carnivorous nature of felines.
Animal Tissue is Also an Essential Source of Vitamins and Water for Felines
As you might have guessed by now, kitties have unique vitamin needs as well.
They have a special requirement for vitamin A, which is available naturally only in animal tissue. Cats lack the intestinal enzymes necessary to convert B-carotene in plants to the active form of vitamin A. Vitamin A is essential for maintenance of vision, growth of bone and muscle, reproduction, and the health of epithelial tissues.
Vitamin D is also essential in the diets of cats because they lack the ability to synthesize it through their skin. The liver and fatty tissue of animals is rich in vitamin D.
Domestic cats evolved from desert-dwelling ancestors, which is why they must get most of their water from the food they eat.
Felines are not as responsive as other animals to sensations of thirst or dehydration. When fed a dry food diet, cats aren't driven to search for another source of water to make up the difference between what their bodies require and what their diet provides.
This results in chronic mild dehydration, a condition that will ultimately result in disease, especially of the feline lower urinary tract and kidneys
Decades of Dry Food Diets Have Produced Legions of Fat, Sick Cats
Ten years ago, estimates were that 25 to 33 percent of house cats were overweight or obese. Today, that number is 55 percent.
Ten years ago, energy-dense, starchy dry foods were identified as a significant contributor to the problem of obesity in felines. (Because, as noted earlier, carbs not used for energy -- which are the majority of carbs in a cat's diet -- turn to fat.)
Ten years ago, we knew that 'weight-loss diets' low in fat and high in fiber may take weight off, but at the expense of lean body mass. We knew then many of these diets contained high amounts of insoluble fiber, which causes more pooping and fecal water loss in cats that aren't consuming enough water to begin with, thanks to their dry diets. We also knew high fiber diets negatively affect nutrient digestibility.
Ten years ago, we were linking dry cat food to feline diabetes, idiopathic feline hepatic lipidosis, dietary intolerance and inflammatory bowel disease (IBD).
Yet today, 10 years later, with more than half the cats in the U.S. overweight or obese, the majority of veterinarians and cat owners remain blissfully unaware of the connection between fat, sick cats and dry cat food.
Hopefully if I keep talking about this, and so does Dr. Jean and others like us... and with the help of readers like you and other knowledgeable cat owners and guardians... we can turn this trend around and begin providing species-appropriate nutrition to the remarkably unique and deserving feline creatures in our care.