Cells, the tiny units that make up the human body, need a regular source of energy to perform their basic functions, and they receive this energy from digested food. According to the National Center for Biotechnology Information, the nutrients stored in food also provide the materials that cells need to create new cells and molecules.
Molecules of food are held together by chemical bonds that contain stored energy, explains Scitable by Nature Education. When the digestive system breaks down these foods by breaking those bonds, it releases that energy, as noted by GroupHealth. GroupHealth further explains that the energy is then converted into a form that cells can easily use, usually glucose, to fuel their operations.
The glucose transitions from the digestive system to the circulatory system, where it travels throughout the body through the blood vessels, according to the University of Illinois at Chicago. The blood delivers this energy to all of the body's systems and organs.
Heart cells, for example, need energy to keep the heart beating, as explained by the McKinley Health Center, and the lung cells need energy to sustain breathing. When the body does not get enough energy to sustain its fundamental processes, it stops working and eventually dies.