Plants make all the energy and phytochemicals they need from sunlight and air, with the help of water and minerals they draw up through their roots. We can't do that; we get our energy and raw materials from food. We eat plants, and animals that have eaten plants, to get all the nutrients our bodies need to grow, reproduce and stay healthy.
Human nutrition is fascinating; if you'd like to know more, check the Recommended Books and Useful Websites. The next several pages explain all of the nutrients we need to get from our food.