# The Naked Scientists Forum

### Author Topic: How are calories in food calculated?  (Read 5978 times)

#### foram joshi

• Guest
##### How are calories in food calculated?
« on: 03/10/2008 22:02:38 »
foram joshi  asked the Naked Scientists:

Dear naked scientists,

My name is Foram and i live in the KSA. just want you all to know that you are doing a great job out there.

i study in the eleventh grade  and i and my friends love your podcasts. we listen to them regularly. they are a lot of fun and have got loads of new things to know! keep up the grrrrrreat work!!!

I also have a question for you:

A label  of every food on the supermarket shelves tell us how many calories there are in it .i know what a calorie is-its an amount of energy-but how do they determine how much energy the food will actually give you? do they feed it on rats and put them on treadmills to see how far they can run?

What do you think?

#### RD

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##### How are calories in food calculated?
« Reply #1 on: 04/10/2008 00:34:29 »
Using a calorimeter like this one.
The food is burned (in pure oxygen) and from the temperature increase it is possible to calculate
the amount of energy (calories/joules) contained in the food.
« Last Edit: 04/10/2008 00:37:16 by RD »

#### Bored chemist

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##### How are calories in food calculated?
« Reply #2 on: 04/10/2008 16:29:57 »
The calorimeter is fine for stuff that gets digested and metabolised ot CO2 but a lot of things are more complicated than that. The fibre in your diet would burn in a bomb calorimeter but it's not used by the body so it wouldn't have any calories as a food.
The usual solution is to analyse the food and calculate the calories on the basis of the fat, carbohydrates and proteins present.

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##### How are calories in food calculated?
« Reply #3 on: 05/10/2008 00:26:44 »
Yes but how?

#### Bored chemist

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##### How are calories in food calculated?
« Reply #4 on: 05/10/2008 11:15:07 »
Add up the bits. Fat is (IIRC about 9 C/g. Proteins about 4 C/g and sugar about 3.5 C/g. Those results are from a calorimeter and you can do that with a pure sugar or protein because it will all be digested. There's also a correction for the fact that nitrogen is excreted as urea rather than N2.
« Last Edit: 05/10/2008 20:28:51 by Bored chemist »

#### The Naked Scientists Forum

##### How are calories in food calculated?
« Reply #4 on: 05/10/2008 11:15:07 »