Food is such an essential part of who we are. We literally take things out of our environment and take it inside of ourselves and make it part of our bodies. For most of human history, that meant things found in nature, plants or animals. Less than a hundred years ago, they started to process food, to take the germ and fiber out of wheat, so it could be stored longer and not go bad. They took the corn plant and wrested sugar out of it (high fructose corn syrup). They feed corn to cows, who naturally eat grass, not grain. And they feed cows growth hormones to produce more milk, and antibiotics so the cows don't get sick. There is more e-coli bacteria in their system because they are eating corn and not grass. It's hard to eat meat for a while after seeing "Food, Inc."
We are omnivores, we have the teeth to digest both plants and animals. But so many of the processed foods are full of chemicals, that really, we have no idea of what they are doing to our health. We see as populations around the world start to eat a western fast food diet, they start having western problems like obesity and heart disease and diabetes. Fast food burgers and super sized sugary sodas and potatoes deep fried in trans fat oils are a recipe for health problems.
Real food comes from nature. It grows in healthy soil, comes from a diverse ecosystem. Real food takes some time to prepare and cook. It doesn't usually come out of a box.