How do they figure out calories in food?

Question

I can understand if they say an about amount, but how do they know the exact amount of calories are in a meal, piece of food, etc.

Also, is it the same for how many grams of fat,etc.?

Answer 1

Scientists measure calories with a calorimeter, and the definition of a calorie is based upon it's ability to raise the temperature of water. What we call a calorie is really a kilocaloriee, since a real calorie is too small to be significant.

Scientists long ago determined the calorie content of foods.

Both protein and carbohydrates contain 4 calories per gram. Fat contains 9 calories per gram. With these numbers it's easy to determine the calorie content of any food.

For example - An item with 100 grams of protein and carbohydrates, no fat, will have 400 calories.

Answer 2

They burn it and they measure how much heat it gives off.

Because that's basically what your body does to get energy from food- it converts it from

C6 H12 O6 (sugar) + 02 (oxygen- what you breath in)

into

2 CO2 (carbon dioxide- what you breath out)+ H2O (water).

(The numbers should all be small and slightly below the line the rest of the equation is written on, apart from the one before the CO2, which should be normal size, as it signifies 2 carbon dioxide molecules.)

Fat has to be converted to sugar before it can be used as energy. Any energy in the food you've eaten that isn't used is converted to fat for storage.

Answer 3

there is a book called the complete book of food counts... go buy it, its great

Answer 4

a calorie is the amount of energy needed to raise one gram of water by one degree C. What they do is put one gram of water in a test tube and mark down the temperature.  Then, they measure how much mass is in the food item, and place it under the test tube of water to burn it.  After burning it, they record the water temperature and find it's change, and then measure the food's mass again.  Doing some math, they can figure out how much mass of the food was needed to raise the temperature one degree C.

We did this experiment in Biology.