Commercial pet food is regulated in the United States by the Association of American Feed Control Officials (AAFCO), which establishes nutrient profiles for dogs and cats and the feeding trial protocols required to substantiate 'complete and balanced' claims on labels. There are two pathways to this claim: meeting AAFCO nutrient profiles through formulation, or passing a feeding trial where animals eat the food as their sole diet for 26 weeks with stipulated outcomes. Feeding trial substantiation is more rigorous but far less common — most pet foods meet nutrient profiles on paper rather than demonstrating real-world adequacy in live animals.

Cats are obligate carnivores with fundamentally different nutritional requirements than dogs. They require preformed arachidonic acid (cannot convert linoleic acid), taurine (cannot synthesize adequately from precursors, unlike dogs), preformed vitamin A (cannot convert beta-carotene), and very high dietary protein — cats use protein for energy even when carbohydrates are available, unlike dogs and humans who spare protein when carbohydrates are present. This is why feeding cats dog food causes serious nutritional deficiencies over time, and why vegetarian diets for cats are nutritionally inappropriate without careful supplementation. The 1987 feline dilated cardiomyopathy epidemic was traced directly to taurine-deficient commercial cat food.

The grain-free pet food trend generated significant regulatory attention when the FDA investigated a potential association between grain-free diets and dilated cardiomyopathy (DCM) in dogs. Between 2018-2020, the FDA received reports of DCM in dogs fed grain-free diets containing legumes, potatoes, and sweet potatoes as primary ingredients. The proposed mechanism involved reduced taurine bioavailability or absorption, though the causal relationship remains unproven. The FDA's investigation was inconclusive about causation, but the episode highlighted that 'natural' and 'grain-free' marketing language does not imply nutritional superiority — ingredients unfamiliar to ancestral diets may have unintended metabolic effects.

Raw feeding (BARF — Biologically Appropriate Raw Food) has passionate advocates and significant safety concerns. Proponents cite evolutionary appropriateness and anecdotal improvements in coat, digestion, and energy. The American Veterinary Medical Association, American Animal Hospital Association, and FDA all warn against raw diets for pets due to documented risks of Salmonella, Listeria, E. coli, and Toxoplasma — pathogens that can sicken both pets and human household members. A 2018 study in Vet Record found 25% of commercial raw pet foods tested positive for Salmonella and 54% for Listeria. Pets fed raw diets shed these pathogens in their feces, creating household contamination risk particularly for immunocompromised individuals and young children.