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 commonly used as shorthand for kilocalorie. You will find this written as kcal on food packets. Kilojoules (kJ) are the equivalent of kilocalories within the International System of Units, 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 eating a healthy, balanced diet with fewer calories while increasing your physical activity.
For more information on weight loss, download the NHS weight loss plan, our free 12-week diet and exercise plan.
You should get advice from your GP if you’re underweight (your body mass index is less than 18.5).
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?.