Cats, carbohydrates, and grain-free diets.

Cats are carnivores that naturally adapt to maintain a healthy blood glucose level despite a low carbohydrate intake. A classic example of a cat's diet is a rodent carcass consisting of roughly 55% protein, 38% fat, 9% carbohydrate, and 1.2% fiber on a dry matter basis. Cats are carnivores, and adapting to a high-protein diet is essential, as adult cats require 2 to 3 times more protein than adult omnivores, while kittens need 1.5 times more protein than the young of non-carnivorous species.

This combination of natural adaptation to a high-protein diet and the delay in using dietary carbohydrates has shaped the recent argument that carbohydrates should constitute only a small fraction of the average domesticated cat's diet.

As a companion animal nutritionist and a cat lover, I always search for answers regarding our current cat nutrition options. How did we come to feed our cats diets so high in carbohydrates?

Cats are not small dogs. Their anatomy, metabolism, and taste preferences differ from those of dogs. If you examine a cat's teeth and compare them to a dog's, you will find that the dentition varies significantly. Adult cats have only 30 teeth, while adult dogs have 42. Additionally, cats possess far fewer molars and premolars. These types of teeth are used for grinding and chewing plant materials.

Today, we recognize 30 closely related species within the family Felidae. All felids are very similar in terms of anatomy and physiology. None of these cats evolved to digest food containing more than 10% carbohydrates, neither the lion in the wilderness nor the pocket panther in your house.

Comparing the NRC nutrient requirements for dogs and cats reveals notable differences. Cats have higher requirements for protein, Vitamin A, and taurine.

Some of the critical differences between our carnivorous cats and omnivorous dogs are:

1)    Vitamin A

Cats produce very few or no enzymes that break down plant-produced carotenoids. They must consume preformed active Vitamin A, which is sourced from the meat of other animals. In contrast, dogs possess enzymes in their intestinal lining that can break down plant carotenoids and convert them into active Vitamin A.

2)    Dietary Protein

If both have a perfectly balanced and 100% digestible protein, the cat will utilize 20 percent of that protein for growth metabolism and 12 percent for maintenance. The dog will require only 12% for growth and just 4% for maintenance.

Cats need much more protein than dogs.

3)    Taurine

Taurine is an amino acid distributed throughout most body tissues. It is essential for the healthy functioning of the heart, retina, bile fluid, and specific aspects of reproduction. Taurine is nonexistent in plant tissues.

Cats cannot synthesize taurine in their bodies, so they must consume preformed taurine found in meat. Taurine is essential for cats, while dogs can synthesize taurine internally.

Now, let's look at the history of the pet food industry.

The story of carbohydrates in cat food began during World War II, when the pet food industry was compelled to stop packaging food in metal cans. As a result, they had to find alternative methods to ensure the shelf stability of dog and cat food. In 1950, the dry food extrusion process was invented.

The mixture can be fed into a machine and cooked under pressure before extruding through small holes to create kibble. The extrusion process requires starch or carbohydrate matrices to form kibble that does not disintegrate and remains crunchy.

At the same time, the pet care industry underwent significant changes and faced numerous challenges. Veterinary clinics began to open in cities and suburbs, specializing in caring for the growing number of pet dogs and cats. In the 1960s, these clinics started selling dog and cat food. In 1976, Colgate-Palmolive acquired Hill's. Today, cat owners have become accustomed to the convenience of scooping food into a bowl.

Today, the pet food extrusion process has undergone significant evolution. Different equipment is being used, and numerous high-meat formulations are available for purchase. However, the process of extrusion still requires a certain amount of carbohydrates to maintain the kibble's stability. Grain-free has become a marketing tool, but it does not necessarily equate to carbohydrate-free and is not a quality indicator.

Many diets substituted corn, wheat, rice, or oats with legumes like beans, peas, or lentils. The edible seeds of legumes are called pulses.

When companies launch diets, their formulators consider the available ingredients to solve the puzzle of a complete and balanced diet. Numerous ingredient options and combinations are available to achieve a balanced cat food diet with a suitable nutritional profile.

Once the animal digests the pet food, it breaks down into nutrients, which are absorbed by the body and ultimately excreted through feces and urine. Cats have adapted well to a human-made diet and must obtain all 44 essential nutrients from their food. The origin of these nutrients becomes of interest when comparing bioavailability and digestibility data of ingredients.

Research is investigating the bioavailability and digestibility of ingredients while comparing their nutritional values in tests. Feline nutrition research lags behind canine nutrition research.

As of today, there is insufficient concrete evidence to mandate the ideal carbohydrate content of a domestic cat's diet.

Cats are obligate carnivores that require meat-based diets to supply all the essential nutrients. However, they can effectively metabolize complex carbohydrates.

With certain metabolic conditions, a limited intake of protein or fat is necessary, which unavoidably increases dietary carbohydrate intake. The veterinarian must consider each patient and determine the ideal nutritional strategy based on that patient's life stage and disease status.  

Perhaps in the future, when more long-term studies are published, a standard recommendation for the macronutrient composition of the average healthy cat's diet will be established. For now, it seems wise to focus on maintaining a healthy caloric intake, exercise, and enrichment to help cats achieve a lean body weight rather than concentrating on the carbohydrate content of their diet.

References:

Council, N. R. (2006). Nutrient Requirements of Dogs and Cats. The National Academies Press. https://doi.org/10.17226/10668

Murphy, M., Bartges, J., Kirk, C., Witzel, A. L., Hamper, B., & Raditic, D. (2012). Current Controversies in Feline Nutrition. In The Cat (pp. 289–298). Elsevier. https://doi.org/10.1016/B978-1-4377-0660-4.00019-3

Pathak, A., Asediya, V., Anjaria, P., & Singh, S. P. (2024). Nutritional and metabolic diseases of dogs and cats. In Introduction to Diseases, Diagnosis, and Management of Dogs and Cats (pp. 429–457). Elsevier. https://doi.org/10.1016/B978-0-443-18548-9.00029-9

Wu, G. (Ed.). (2024). Nutrition and Metabolism of Dogs and Cats (Vol. 1446). Springer Nature Switzerland. https://doi.org/10.1007/978-3-031-54192-6