Ratsasan (pronounced "Raatchasan", transl. Demon) is a 2018 Indian Tamil-language crime thriller film directed by Ram Kumar. The film features Vishnu Vishal and Amala Paul in the lead roles, while Saravanan, Kaali Venkat, and Ramdoss play supporting roles. The film tells the story of an aspiring film director who becomes a police officer after his father's death and tries to track down a serial killer.

The energy needs of the human body must be fulfilled despite the fluctuations in nutrient availability that the body experiences on a daily basis. How, then, do our different cells use fuel molecules, and what factors are involved in this process? We can think of the human body as a dynamic environment where each cell has to continually and sometimes cyclically switch the type of substrate that is oxidized and/or produced. This adaptation is crucial and is achieved only through the several regulatory mechanisms involved in controlling energy transformation and utilization. Moreover, cellular adaptation becomes more crucial when we consider the diverse physiological conditions an organism is exposed to on a daily basis. For example, during the night we usually do not eat, a type of "fasting" that is later disrupted by breakfast, and at other times we are simply resting, or exercising. In these situations, the type and amount of nutrients available for cells change abruptly.