Federal law defines the characteristics and conditions for a medical food used to treat disease in humans, but there is no equivalent definition for animal products. The Food and Drug Administration (FDA) allows products intended to serve as a component of the treatment regimen of an animal's disease while supplying the animal's daily nutritional needs to be marketed without being subjected to the drug approval process and to be regulated as a food rather than a drug. Veterinarians who recommend a therapeutic or prescription-type diet are responsible for ensuring safety and assessing effectiveness. The FDA believes that these products should generally not be available outside of a valid veterinary-client-patient relationship.

Studies have statistically shown the benefit of a commercially available product to delay uremic crises and extend the lifespan of a clinical population of dogs. The studies showed the effect of the overall diet as opposed to the effects of specific nutrients. Osteoarthritic changes of a group of Labrador retrievers were decreased in a group fed 25% less food when they were puppies and adults compared with littermates that were fed ad libitum. Thus, several commercial formulas have adjusted the energy density and macro- and micromineral content of growth products for large and giant-breed dogs. Reduction of food intake has been shown to increase the median lifespan of dogs and delay the onset of clinical signs of chronic disease. These findings are similar to results from a variety of species. Dogs may also provide a useful model for dementia. A proprietary commercial diet containing a broad spectrum of constitutive and novel antioxidants significantly improved the performance of older beagles on several discrimination learning tasks.

Many foods are marketed for digestive and absorptive disorders. Approximately 90% of the digestion function and capacity of dogs and cats occurs in the small intestine, so diseases that disrupt digestion or absorption in this region can be challenging to treat. Fat restriction is a common recommendation and, while the extent to which fat should be restricted may be controversial, most authors agree that demonstration of patient tolerance is one of the best criteria.

COMMENTARY: Many therapeutic diets have been suggested since the commercial introduction of the first diet in 1948 to aid in treatment of dogs with renal disease. Veterinarians need to understand the differences among various products as well as the type and quality of research that goes into their development.

Nutrition, prevention and treatment of disease in dogs and cats. Burkholder WJ. ACVIM PROCEEDINGS, 2003, pp 1-3.