Resting energy expenditure (REE) is a term that describes the number of calories that someone burns in a day without any strenuous activity. There are a number of ways to estimate a person's metabolic rate, which directly impacts resting energy expenditure, but it is very difficult to get a completely accurate measure of someone's REE without the use of expensive equipment. Having at least a rough measure of resting energy expenditure, though, can be very important because it can help someone determine how many calories he or she can consume in a day without gaining or losing weight.
Part of the reason that it is difficult to determine resting energy expenditure is that there are a number of variables that determine someone's metabolic rate. Resting energy expenditures vary between men and women, for instance. Also, the height and weight of an individual have a very large impact on the REE. As a person ages, his or her metabolism slows down, and thus his or her resting energy expenditure decreases.
Though accurately accounting for all of these factors is very difficult, there are methods available to get a precise measure of someone's resting energy expenditure. A calorimeter can effectively determine someone's metabolism by measuring the amount of heat that the body mass produces. Another method is to use an analysis of the gases that a subject respires in order to derive the volume of the air passing through the lungs. This can provide an indirect measure of the body's metabolism. Both of these methods are complicated and potentially expensive.
Far more often, subjects use one of any number of formulas for determining the metabolism and the resulting resting energy expenditure. One of the most common of these is the basal metabolic rate, or BMR, combined with the Harris Benedict equations. The BMR formula accounts for several of the primary variables that determine a person's metabolism. The Harris Benedict equation uses the BMR but adjusts the final value depending on the amount of activity in which a person tends to engage. The resulting measures are not completely accurate because they do not consider the ratio of lean muscle mass to body weight, which can have a large effect on REE, but they still can provide a sufficient guideline for daily caloric expenditure.
Regardless of the method of determining the resting energy expenditure, it can be very important to get at least a rough measure of REE. Knowing REE can help someone maintain their weight, especially when that person undergoes some sort of lifestyle change, such as those resulting from injury or disease states. Similarly, athletes who are trying to gain weight can use their REE to know how many calories they will need to consume each day.