Energy is needed for your body to function - from even the most basic activities in your cells, to keeping your heart pumping blood around your body so, whether you're asleep or running a marathon, you need energy.
The science bit
Energy is measured in calories or kilojoules. On our products you may see this written as kcal for calories and kj for kilojoules. Energy takes into account your overall intake of all nutrients - carbohydrates, protein, fat and alcohol.
These nutrients provide a different amount of calories per gram. In the UK we usually measure energy in kcals. 1g of carbohydrate is worth 3.75kcal; 1g protein is worth 4 kcal; 1g fat is worth 9 kcal and 1g of alcohol is worth 7 kcal.
How much do I need?
The guideline daily amount for energy if you're a man is 2500 kcal and for women it's 2000 kcal. Children have different energy requirements specific to their age. Because they're still growing and may be very active it's important to make sure they're eating enough.
At different times of life and in different circumstances, you'll need different amounts of energy. This is especially important to remember for children and elderly people, who may need more energy for growth or when ill.
If you take in more calories than you use, you will put on weight. If you use more calories (energy) than you eat in food you will lose weight. If you're trying to manage your weight, this is important to remember. If you are at all concerned about a new diet you are about to start, speak to your GP.