Any substance that promotes growth with living organisms. The term is generally applied to nitrogen and phosphorus in wastewater, but is also applied to other essential and trace elements. Nutrients, which include carbohydrates and fat are primary substances needed for correct bodily functions. Nutrients must be existent in the food due to their inability in synthesizing within cells. These body functions consist of generating heat and power, maintaining good balance within the body, and growing important tissues such as bones and muscles, in addition to blood and teeth.