Energy requirements

For anything in our bodies to work, we need energy! Just as a car goes nowhere without fuel, our bodies cannot function for any length of time without energy. Our energy requirements, i.e. the amount of kilocalories (commonly referred to in everyday language as simply “calories”) we need, depend on a range of factors including our age, gender, bodyweight and level of physical activity. Young people need more energy in relation to their bodyweight than older people, men need more than women, and if you are physically active, you need more energy than someone who is relatively inactive.

Our energy requirements are calculated on the basis of our basal metabolic rate and our active metabolic rate. The basal metabolic rate is the amount of energy we need to keep our heart beating, to breathe, and for our bodies to maintain the correct temperature. This basal metabolic rate is combined with our active metabolic rate, i.e. the amount of energy we need to do sport or to work, for example.

The table below indicates the amount of energy we need (in kcal per day). The values apply to individuals with moderate physical activity, such as students or motorists who spend some of their working time sitting and some of it standing, and are physically active in their free time.

We provide our bodies with the energy we need in the form of food. More precisely, it is the nutrients contained in the food, such as carbohydrates, protein, fat and also alcohol that contain the calories. Energy content is measured in kilocalories (kcal) or kilojoules (kJ), where one kilocalorie is equivalent to 4.2 kilojoules. Each nutrient does not provide an equal amount of energy: fat is the most energy-rich with 9 kcal per gram, while protein and carbohydrates, at 4 kcal per gram, provide only half as many calories. One gram of alcohol contains 7 kcal. Depending on the composition, therefore, every foodstuff and every beverage has specific calorie content.

Energy intake and energy consumption determine our bodyweight. If we aim to maintain a normal bodyweight), our energy intake must be adapted to our energy requirements. If we take in less energy than our body need, our bodyweight will fall. If we take in more calories than our body need, our weight will rise.

Table: Reference values for average daily energy intake (kcal)