Introduction to energy aspects of nutrition
The Standard International unit of energy is the joule, which is defined as the energy expended when a mass of 1 kg is moved through a distance of 1 metre by a force of 1 Newton. Plants “trap” energy from sunlight and use it to make sugars in the process of photosynthesis. Photosynthesis is the ultimate source of all the energy in living systems and fossil fuels. The oxidation of foodstuffs in metabolism is often linked to the oxidative processes of combustion or burning. Dietary recommendations and survey reports often quote carbohydrate, fat, protein and even alcohol intakes as a percentage of total energy. The energy density of a food or diet is the metabolisable energy yield per unit weight of food. Malnutrition predisposes to infection, and infection increases the severity of malnutrition or may precipitate malnutrition in areas where there is no overt food shortage.