How do they measure the calories in food?

Calories are a measure of how much potential energy the food possesses.

Just an interesting sideline: A calorie is a unit of energy. We tend to associate calories with food, but they apply to anything containing energy. For example, a gallon (about 4 liters) of gasoline contains about 31,000,000 calories. You could drive a car 22 miles (35 km) on the calories in 217 Big Macs.

Specifically, a calorie is the amount of energy, or heat, it takes to raise the temperature of 1 gram of water by 1 degree Celsius (1.8 degrees Fahrenheit). One calorie is equal to 4.184 joules, a common unit of energy used in the physical sciences.

Most of us think of calories in relation to things we eat and drink, as in "This can of soda has 200 calories." It turns out that the calories listed on a food package are actually kilocalories (1000 calories = 1 kilocalorie). So that can of soda actually has 200,000 calories (but don't worry, the same applies to exercise -- when an exercise chart say you burn 100 calories jogging a mile, it means 100,000 calories). A food "calorie" is sometimes capitalized to show the difference, but usually not.

Now.. as to HOW food calories ares measured.. is somewhat simple... Food labels always contain the number of calories per serving. But how is this number determined? The answer is surprisingly simple: The food is burned. A sample of the food is placed in an insulated, oxygen-filled chamber that is surrounded by water; this chamber is called a bomb calorimeter. The sample is burned completely. The heat from the burning increases the temperature of the water, which is measured and which indicates the number of calories in the food. For example, if water temperature increases by 20 degrees, the food contains 20 calories. This method of measuring calories is called direct calorimetry.

When the body "burns" food to produce energy, oxygen is used and carbon dioxide and heat are produced. Scientists have developed ways to measure the amount of calories burned in activities by measuring either of these 3 components. The most precise is the room calorimeter where a subject may

remain for several days and the amount of heat produced by the body is determined by measuring how much heat is absorbed by the surrounding walls.

We covered this in biology. Basically they burn a food and they see how much the heat created raises the temperature of water. The more a food raises the temperature, the more calories it had. We did it in a biology class with peanuts.

On another note fats have more calories per gram than any other food, hence why you should avoid them!

A calorie is a way of measuring the amount of energy something has. Specifically, the amount to energy it takes to raise the temperature of 1 gram of water by 1 degree celcius. When something has a lot of calories it means there is a lot of energy in it. I know this doesn't really answer your question but I hope this helps somewhat.

Hi - I think there has been a mistake above re kilocalories. KILOJOULES are another measure of energy. There are about 4.4 kilojoules per calorie. Therefore kilojoule levels in a food/drink are always about 4 times higher than calorie levels. Aussies often refer to the amount of kilojoules rather than calories. 4400 kilojoules contain the same amount of energy as 1000 calories.

A "bomb calorimeter" is used to determine the calorific value of foodstuffs. However, the calorific value of most processed foods purchased are simply calculated by tallying up the quantities of fat/carbohydrate/protein within each of the added ingredients and then multiplying the amount by 9 kcal/g for fat and 4 kcal/g for carb/protein.

Great animation of bomb calorimeter at http://web.umr.edu/~gbert/animation.html.

not an indepth answer - but they burn the food and the amount of energy given off shows how many calories is it it

u will need a right smartarse to tell u more than that

Burn a weighed amount of food in a stream of oxygen and absorb the heat in water. You got some maths to do then.

4 calories per gram of carbohydrates,

4 calories per gram of proteins,

9 calories per gram of fats.