|MadSci Network: Biochemistry|
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. This is a very technical process and not easily done, but there are at least three centers in the United States where this is measured. It is much more common to measure either the amount of oxygen consumed or carbon dioxide produced. Exhaled air is collected during exercise and the amount of oxygen used is determined. This is also a tedious process and requires an oxygen analyzer. Interesting the amount of air that is exhaled compares well with the amount of energy used, so a short-cut method to measuring energy expenditure is measure the amount of air exhaled and compare to a the volume expired in experiments when oxygen was actually measured. This is not as exact, but gives useful information. It has even been proposed to simply count the number of breaths taken since this also correlates to energy expended, but you can see this would be even less precise. All of these methods require the use of equipment that is bulky. Scientists have searched for easier methods to measure energy expenditure. Some devices measure the amount of movement, such as a pedometer that measures steps or accelerometer that measures movements, to estimate energy expenditure. This is less accurate, but very practical and yields useful information. Phyllis Stumbo University of Iowa
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