Food energy
Foods have different energy, or caloric, values because they contain varying combinations and amounts of protein, fat, carbohydrate and water. For example, a 50 gram (VA ounce) serving of cauliflower supplies only seven calories while a wholemeal roll of the same weight provides 135.
MEASURING FOOD ENERGY The energy in the foods you eat is measured in units called calories, which is the energy needed to raise the temperature of one milli-litre of water by 1° Centigrade. But since this is so small, health and nutrition professionals
usually speak of calories in units of 1000, called a kilocalorie or Calorie (with a capital ‘C’). These measurements are usually abbreviated as kcal or cal. You may sometimes see a reference to a kilojoule. This refers to an even smaller unit of calories: 4.18 kilojoules equal one calorie.
Basic nutrients differ in their energy content. A gram of either pure carbohydrate or protein contains four calories. A gram of pure fat, however, contains nine, while a gram of water has no caloric value. The caloric value of a food only indicates its energy level and does not describe the proportion of other nutrients, such as protein, carbohydrates, vitamins and minerals. Therefore, if a food is high in calories it is not necessarily high in all nutrients.
Everybody needs a certain amount of energy from food simply to maintain basic bodily functions such as breathing, blood circulation and body temperature when the body is at rest. This is called the basal metabolic rate (BMR). Further calories are necessary for the body to be active. The number of calories each
individual requires varies enormously, depending on age, sex, size and metabolic rate. For example, a sedentary woman aged 65 years weighing about 54.5 kilograms (120 pounds) burns about 1500 calories a day whereas an active 25-year-old active woman weighing the same requires about 2000 calories to fuel her body.
