The first function of life is to become alive. The second is to survive. To survive, we have to eat, and each of us has a different prescription in nature. Our bodies and our minds are designed for a particular diet.

The problem nature runs into is that some animals have to kill other sentient, thinking beings to stay alive, and that collides with the first goal of life, which is simply to be alive. So nature built prototypes. Some went off to eat flesh and kill. Others eat only plants. Some can eat both. But nature may be working toward a creature that needs only the sun, an animal that can turn sunlight directly into its own energy and flesh. That may never happen.

Humans are an incredible prototype. Our instincts have been pulled back far enough that we have access to free will through intelligence, and we have adaptive bodies, which means we can live on plants. When we eat plants, we skip the middleman. The animal ate the plants. We go straight to the source.

It gets confusing because animal foods have been available to humans since the beginning of time. We learned by watching other animals, and by being really hungry. Once you have tasted blood, turning into a herbivore is hard. Flesh foods are filling. They satiate, and satiation is relaxing, while hunger creates anxiety.

To go plant-based, you have to get enough calories from a wide variety of produce. The big problem people run into when they go vegan is that they still eat a lot of junk food, so their bodies never quite feel good. They usually don't know what to eat either, so they slip into a calorie deficit.

Processed food, of course, is a different category altogether. No creature was designed to eat food that disrupts the endocrine system and intoxicates instead of nourishing it.