All animals are biologically-equipped to assimilate and digest foods. For example, earthworms are naturally designed to process dirt. The entire GI tract of worms, from the mouth to the end of the waste is excreted, what designed for this purpose.
Cows are designed to eat grass, and their GI tracts are set up perfectly for this. They have big, round, flat teeth used to grind grasses and an unbelievable range of motion in their mandibles, allowing them to chew, chew, and chew. Cows have a lot of range of motion laterally in their jaws.
Dogs and cats do not have this range of motion in their jaws. Your jaws move up and down, like a trap door or a hinge, because dogs and cats are gulpers, not chewers. They do not have chewing teeth. Dogs and cats have incredibly sharp interlocking teeth designed to rip and tear flesh.
They also have very short GI tracts to vegetarian animals that need to ferment foods, as carnivorous animals consume foods with potentially very heavy pathogen loads. The bodies of carnivores are designed to get food in and back out very quickly.
The ancestral lifestyle of a carnivore includes lots of variety and seasonal variability, meaning certain prey. They are thriving consuming fresh, living, whole animals. But carnivorous animals do not eat clean foods. Dogs and cats did not evolve to consume sterile foods. They have digestive tracts that are designed to be the cause of the disease. Their food in the wild is moisture-dense, meaning the prey.
The carnivorous lifestyle requires a tremendous amount of exercise and exertion. Food was not served to them, so they had to stealthily catch it. This stimulates the nervous system, skeletal, endocrine, and circulatory system involvement. Carnivorous animals had daily rigorous workouts in an attempt to catch enough food to stay alive.