All food comes from the ground from the action of the sun and photosynthesis and water from the ground and co2 from the air. From green plants. If all the world ate green plants there would be no starvation because plant eating ( primary step) is totally sustainable. But we have the choice to eat the plant or we eat the animal that has eaten the plant or we eat the animal that has eaten the animal that has eaten the plant. In this way the food energy is passed from one food chain up to the next chain. Each step higher up is more wasteful as it involves more creatures to feed .So the human carnivorous diet is shockingly wasteful. This is the food chain or web. It is a major cause of world starvation and climate changes.