Figure 1. Energy homeostasis depends upon the balance between caloric intake and energy expenditure.

Although caloric intake is almost entirely due to the consumption of food (minus whatever fails to be absorbed), energy expenditure has more components, including basal metabolism, physical activity (voluntary and involuntary) and adaptive thermogenesis. The last category includes the small amount of energy spent in absorbing and processing the diet (known as diet-induced thermogenesis) as well as energy spent to maintain body temperature in the face of cold.