Any discussion about the nutritional needs of cats invariably starts by talking about protein. Cats are carnivores and as such have developed distinctive physiological pathways for utilizing protein. One of the most elegant explanations about what makes cats unique (nutritionally speaking, at least) can be found in "Effects of nutrition choices and lifestyle changes on the well-being of cats, a carnivore that has moved indoors," written by Debra Zoran, DVM, PhD, DACVIM and Tony Buffington, DVM, PhD, DACVN.
The article appeared in the September 1, 2011 issue of the Journal of the American Veterinary Medical Association (JAVMA). Here are a few excerpts:
Today, of all companion animals, domestic cats retain the most anatomic, metabolic, and behavioral features of their predecessors. Domestication has changed cats relatively little.
The natural diet of cats in the wild is based on consumption of small mammals, birds, and insects (i.e., meat- or protein-based diets). Such diets contain little carbohydrate.
Cats are one of the few species that are strictly carnivorous, which explains their unusual requirement for specific nutrients, such as arachidonic acid, vitamins A and D and many B vitamins (particularly niacin), taurine, and arginine, which cannot be endogenously synthesized in sufficient amounts to meet their needs. However, it is their unique need for large amounts of dietary protein (specifically, dispensable nitrogen) that separates them from noncarnivorous species. Many of the dietary requirements for specific amino acids, fatty acids, and vitamins that have been observed in cats are suggested to be a result of their evolutionary adaptation for food availability from animal sources.
Several reviews of feline nutrition provide details of the specific needs that dictate their diet composition. Although healthy animals of many species can accommodate large amounts of dietary protein, cats are particularly adapted both physiologically and metabolically for high protein intake (diets containing 70% protein are acceptable for cats) as a result of the high, fixed rate of activity of the enzymes of protein degradation and disposal (including aminotransferases and urea cycle enzymes) in cats. This unique aspect of feline enzyme function was clearly evident in a study in which investigators found that the activity of some hepatic aminotransferases and urea cycle enzymes did not differ when cats were fed diets high (54% ME) or low (14% ME) in protein.
Conversely, in noncarnivorous species, the same changes in diet resulted in multiple-fold decreases in enzyme activity when the low-protein diets were fed. Furthermore, this lack of enzyme adaptability to dietary protein intake in cats was found to be most relevant in cats fed diets that were inadequate in protein (contained less than the NRC minimum of 16% ME or < 1.6 g of protein/d).
Thus, this lack of metabolic flexibility becomes critically important when cats are inappetent (as a result of disease or other health conditions, including gastrointestinal tract disturbances or hepatic lipidosis), are consuming diets containing poor-quality protein, or are not consuming a sufficient amount of protein in the diet to meet their needs (e.g., inadequate amounts of protein in a diet that is fed to induce weight loss).
I usually don’t recommend that pet owners seek out articles from veterinary journals. They can be so dry and technical that even veterinarians have difficulty wading through them. This piece is an exception. Sure, it goes into more detail than many owners might want, but it provides such good information about the associations between diet, feeding behaviors, and environmental influences with disease that it is well worth your time.
If your local library doesn’t carry JAVMA the article is available for purchase ($30) at the AVMA’s website.
Dr. Jennifer Coates