Within a healthy balanced diet, a man needs around 10,500kJ (2,500kcal) a day to maintain his weight. For a woman, that figure is around 8,400kJ (2,000kcal) a day.
These values can vary depending on age, metabolism and levels of physical activity, among other things.
What are calories?
Calories are a measure of how much energy food or drink contains. The amount of energy you need will depend on:
- your age – for example, growing children and teenagers may need more energy
- your lifestyle – for example, how active you are
- your size – your height and weight can affect how quickly you use energy
Other factors can also affect how much energy you burn. For example:
- some hormones (chemicals produced by the body) – such as thyroid hormones
- some medications – such as glucocorticoids (a type of steroid used to treat inflammation)
- being unwell
Calories and kilocalories
The term calorie is a commonly used shorthand for "kilocalorie". On food packets you will find this written as kcal. Kilojoules (kJ) are the metric measurement of calories, and you'll see both kJ and kcal on nutrition labels – 4.2kJ is equivalent to approximately 1kcal.
Maintaining a healthy weight
To maintain a healthy weight, you need to balance the amount of calories you consume through food and drink with the amount of calories you burn through physical activity.
To lose weight in a healthy way, you need to use more energy than you consume by:
Download the 12-week weight loss guide.
If you're underweight (your BMI is less than 18.5), you should get advice from your GP. To gain weight, you need to eat more calories than your body uses each day. For more information, see How can I gain weight safely?
Read the answers to more information about food and diet.