Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: Hayley on 11/04/2010 22:30:02

Title: How are calories in food calculated?
Post by: Hayley on 11/04/2010 22:30:02

Hayley  asked the Naked Scientists:
   
What's the most accurate way to calculate calories in a food? And how are calories counted?

Thanks in advance
Hayley

What do you think?

Title: How are calories in food calculated?
Post by: chemrbhs on 09/05/2010 05:12:12

1Cal = 1000cal
1cal = amount of heat required to raise 1g of water 1^oC
The most effective, and possibly only way, to measure cal is to use a bomb calorimeter, an instrument that will ignite the sample of interest and measure the temperature change of a known substance, usually water, form the temperature change of the water you can calculate the amount of heat gained by the water and therefore lost by the sample.
But if you are looking for calorie counts for various foods, pretty much every conceivable food has been calculated and is available on line.
gregory

Title: How are calories in food calculated?
Post by: Bored chemist on 09/05/2010 09:33:13

The result you get by burning in a calorimeter is accurate for simple sugars and fats.
It gives the wrong answer for things with cellulose (which would burn, but is not digested by the body) and it also gives the wrong answer for proteins because the end product of their metabolism is urea which you don't get by burning.
The calculations are a bit more involved but, as has been said, the simple way to find a calorie count s to look it up.