All animals— including our cats and dogs—need nutrients (i.e., specific amino acids, vitamins, minerals and fatty acids) that are found in ingredients (i.e., meat, eggs, seeds, fruit, vegetables, etc.) in order to survive.
In the wild, feral cats and dogs obtain their essential nutrients by consuming whole, raw prey, such as mice, rats, birds, rabbits, lizards and insects.
The contemporary dog and cat consume a diet that looks very different from that of their ancestors. We feed our companion animals commercial pet food that is sourced from factory farmed animals, such as cows, pigs and chicken. In addition to being a source of nutrients for our cats and dogs, these farm animals are also a source of harmful steroids and antibiotics that have been fed or injected into them.
To turn factory meat into something that looks like dried kibble or canned wet food, heavy manufacturing is required—a process that essentially strips meat of many of its nutrients.
In order for pet food to become nutritionally complete for your cat and dog, nutrients must be added back to kibble and canned wet food. You can find a list of these nutrients under the ingredient label of any commercial pet food.
Most of these nutrients that are added back to commercial pet food come from non-animal sources. In most cases, the nutrients contained in kibble and canned wet food—the nutrients that are essential for your cat and dog to survive—are synthetically or microbially derived.