Principles are highest order or level of type or quality. Ideas below assume evolutionary biology. Belief in special creation may have biased previous generations of scientists and doctors.
In natural habitat, we didn’t optimize digestion of rare or processed foods. Just was not necessary. Evolution (natural selection) did supply us general purpose digestion that was good enough for occasional foods. But are we optimized for any ideal foods, or are we general purpose feeders, remains question of science and opinion.
We are animals, not machines. Animals eat foods whole or minimally processed, as found in nature. Apart from pulling fruit from a tree, leaves from a bush, tubers from the ground or meat from a bone, animals don’t really process food. Humans may have changed that by using fire to cook, but adapted to cooking over millions or hundreds of thousands of years.
But are we optimized for any ideal foods, or are we general purpose feeders, remains question of science and opinion. If eating exclusively plants food prevents and reverses chronic disease, that’s good evidence for plants being ideal foods. Our evolutionary family, hominids or great apes, are herbivores. They primarily eat vegetation, fruits and nuts. Some do occasionally eat meat, insects and honey. This does not make them carnivores, or even omnivores. Animal forms have evolved over time from carnivore to herbivore and back, often many times. All animals have general purpose digestion. We should require extraordinary evidence to prove we are omnivores. Our anatomy suggests we should eat foods similar to other hominids or great apes. We lack claws, fangs, etc. Our vision is attracted to images of produce markets, while generally disgusted by images of butchers. Paleontology suggests we ate animal foods. But bones make better fossils than leaves. When paleontologists look for plant fossils, they find them. Anthropology suggests we eat animal foods. But modern non-civilized humans are confined to the most barren habitats on the planet. By contrast, evolutionary and ancient human probably occupied habitats that were abundant in plants and animals. All of this suggests that plants are ideal foods, and animals are occasional or backup foods.