Energy? Go Get it!

Energy is the power your body needs to exist and work. The human body extracts energy from food which consists of carbohydrate, fat, protein and alcohol. The most common measurement of energy is a calorie (cal). It is defined as the energy necessary to raise the temperature of 1 gram of water by one degree Celsius (from 14.5 to 15.5C). As people need large amounts of energy, when talking about energy, kilocalories (1kcal=1000 calories) are used.

Energy output
The body needs a certain amount of energy to maintain its basic functions - 'basal metabolic rate' (BMR) - plus further energy for any other activity. The actual amount of energy needed for an individual therefore varies significantly with personal BMR and levels of activity. As a rough guide the BMR for men in the UK is around 1,800 kcal per day and 1,200 kcal per day for women. Various activities will require different amounts of energy. You can expend as little as 80 kcal per hour just sitting around and in excess of 500 kcal per hour doing strenuous manual work or vigorous sporting activity. The estimated average energy requirement for students (late teens to early twenties) is around 2,600 kcal for men and 2,000 kcal for women. Individual requirements depend on weight and levels of activity as described above.

Energy intake
The average daily energy intake in the UK is around 2,500 kcal for men and 1,700 kcal for women. It is important to try to obtain the required energy from as healthy sources as possible. Different types of food provide different levels of energy. Carbohydrate provides 3.75 kcal of energy per gram, fat 9 kcal/g, protein 4 kcal/g and alcohol 7 kcal/g.

What comes in must come out!
If energy output is less than intake, the body stores energy in fat tissue and you gain weight. An ideal energy intake will keep the body weight within the desirable range given an individual's level of physical activity.

Further information

This article published on
28 November 2005

Next review date 11/1/2013


Diet and exercise
Diet and exercise
Diet and exercise

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