Understanding calories

Calories are a measure of the amount of energy in food. Knowing how many calories are in our food can help us to balance the energy we put into our bodies with the energy we use. And that’s the key to a healthy weight.
A ‘kilocalorie’ is another word for what is commonly called a ‘calorie’, so 1,000 calories will be written as 1,000kcals.
Kilojoules are the metric measurement of calories. To find the energy content in kilojoules, multiply the calorie figure by 4.2.
The label will usually tell you how many calories are contained in 100 grams or 100ml of the food or drink, so you can compare the calorie content of different products. Many labels will also state the number of calories in 'one portion' of the food. But remember that the manufacturer’s idea of 'one portion' may not be the same as yours, so there could be more calories in the portion you serve yourself.
You can use the calorie information to assess how a particular food fits into your daily calorie intake. As a guide, the average mans needs 2,500kcal (10,500kJ) to maintain his weight, and the average woman needs 2,000kcal (8,400kJ).
Some restuarants put calorie information on their menus, so you can also check calorie content of foods when eating out. Calories should be given per portion or per meal.
You can learn more in Food labels.

Checking the calories you use

The amount of calories people use by doing a certain physical activity varies depending on a range of factors, including size and age.
The more vigorously you do an activity, the more calories you will use. For example, fast walking will use more calories than walking at a moderate pace.

Losing weight

If you’re gaining weight, it usually means you’ve been regularly eating and drinking more calories than you've been using through normal bodily functions and physical activity.
To lose weight you have to tip that balance in the other direction. You must start to use more energy than you consume, and do this over a sustained period of time.
You can do this by making healthy changes to your diet so that you eat and drink fewer calories. Learn more in Food and diet.
The best approach is to combine these changes with increased physical activity. To see if your physical activity levels need a boost, use our interactive Fitness tool.
You can learn more about making healthy changes to your diet in our Lose weight section.
You can also talk to your GP or practice nurse and get more advice on achieving the right energy balance and losing weight.