8Food and Health
Unlike plants that can acquire energy through photosynthesis, animals—being heterotrophs—need to derive energy solely from their food. This is the primary role of food. Furthermore, they extract chemical energy from food to gain energy for cellular activities while synthesizing materials to grow and sustain their bodies. Such processes of substance and energy conversion are referred to as "metabolism." However, since there are differences between food intake/utilization at the individual level and molecular intake/utilization at the cellular level in multicellular organisms, it is necessary for an organism as a whole to coordinate its actions. In addition, being social animals, humans exhibit interactions between activities, such as eating, working, exercise, and rest, and bodily functions and reactions. In this chapter, we will discuss individual—and cellular—level biology pertaining to food and health as mentioned above.