How can calories be measured

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Just try to take in less energy on the following days. Knowing the calorie content of food and drink can help ensure you're not consuming too much. The calorie content of many shop-bought foods is stated on the packaging as part of the nutrition label. This information will appear under the "Energy" heading.

The calorie content is often given in kcals, which is short for kilocalories, and also in kJ, which is short for kilojoules.

A kilocalorie is another word for what's commonly called a calorie, so 1, calories will be written as 1,kcals. Kilojoules are the metric measurement of calories. To find the energy content in kilojoules, multiply the calorie figure by 4. The label will usually tell you how many calories are contained in grams or millilitres of the food or drink, so you can compare the calorie content of different products. But remember that the manufacturer's idea of 1 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. There's a wide range of online calorie counters for computers and mobile phones. Many of these can be downloaded and used for free.

The NHS cannot verify their data, but they can be helpful to track your calories by recording all of the food you eat in a day. Some restaurants put calorie information on their menus, so you can also check the calorie content of foods when eating out. 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'll use.

For example, fast walking will burn more calories than walking at a moderate pace. So if you know how many carbohydrates, fats and proteins are in any given food, you know how many calories, or how much energy, that food contains. If we look at the nutritional label on the back of a packet of maple-and-brown-sugar oatmeal, we find that it has calories. This means that if we were to pour this oatmeal into a dish, set the oatmeal on fire and get it to burn completely, the reaction would produce kilocalories remember: food calories are kilocalories -- enough energy to raise the temperature of kilograms of water by 1 degree Celsius.

If we look closer at the nutritional label, we see that our oatmeal has 2 grams of fat, 4 grams of protein and 32 grams of carbohydrates, producing a total of calories. Of these calories, 18 come from fat 9 cal x 2 g , 16 come from protein 4 cal x 4 g and come from carbohydrates 4 cal x 32 g. Our bodies "burn" the calories in the oatmeal through metabolic processes, by which enzymes break the carbohydrates into glucose and other sugars, the fats into glycerol and fatty acids and the proteins into amino acids see How Food Works for details.

These molecules are then transported through the bloodstream to the cells , where they are either absorbed for immediate use or are sent on to the final stage of metabolism, in which they are reacted with oxygen to release their stored energy.

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