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How is the caloric value of food measured?

Question #116734. Asked by star_gazer. (Aug 14 10 5:08 PM)

serpa

Graduates of 9th-grade science may remember a very simple answer: Burn the food to see how much heat it gives off. That energy can be measured in calories; nutritionally speaking, one calorie is defined as 1,000 times the energy it takes to heat a gram of water from 14.5 to 15.5 degrees Celsius. But instead of burning anything, food laboratories often freeze their samples in liquid nitrogen and then blend them into a fine, monochromatic powder that can then be used in a variety of chemical analyses. In a Kjeldahl analysis, for example, lab techs remove nitrogen from the food powder and then use it to calculate the amount of protein the sample contains. A hexane extraction can gauge the amount of fat. Carbohydrates are usually measured by differenceâ€”they're what is left over when you remove everything else.

http://www.slate.com/id/2099285

 Aug 14 10, 8:44 PM
Baloo55th

See New Scientist of 18 July 2009 for a good article on the wildly differing results that come from the different ways of estimating calories. I refrain from saying 'measuring', as the methods used don't properly (if at all) take into account the processes of chewing and digesting.

 Aug 15 10, 4:37 AM

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