ABSTRACT

This chapter explores the impact of food, physical activity and illness on energy expenditure and requirements. Living organisms require energy to maintain life. Energy is obtained by oxidation of fuels, which include carbohydrates, fats, proteins and alcohol. adenosine diphosphate (ATP) is subsequently used to drive other energy requiring processes in the cell. Such processes include protein synthesis for growth or muscle contraction. Energy (or work) is expressed in the System International (SI) joule unit. The joule is a small unit and, for convenience, food energy is more often expressed in kilojoules (kJ, 1000 joules) or megajoules. The energy available to the human body, or net energy, is in fact slightly less than the gross energy, or that released by combustion in the bomb calorimeter. Metabolic rate measured at the lowest rate of energy expenditure, usually after at least eight hours of rest and ten hours after the last meal, is referred to as basal metabolic rate (BMR).