Some people who have trouble losing or gaining weight would benefit from knowing their metabolism rate. A person's metabolism rate is the rate at which they burn calories. The number of calories a person needs per day is equal to his or her resting metabolic rate (RMR) plus the energy that is consumed by exercise or daily activities. Two methods to measure metabolism are direct and indirect calorimetry.
In the direct method, a person stays in an insulated metabolic chamber for 24 hours. This is the most accurate way to measure metabolism. As a person inside the chamber gives off body heat, it raises a layer of water outside the chamber used to measure temperature. With this temperature, a researcher can calculate the number of calories the person uses.
In indirect calorimetry, the amount of oxygen a person uses is measured. There is a relationship between the amount of oxygen a body uses and the energy it uses, and scientists are able to calculate the number of calories expended from the amount of oxygen used. With handheld devices, a resting person breathes into a mouthpiece that measures the ratio of oxygen to carbon dioxide. This ratio determines how efficiently a person uses oxygen, which corresponds to his or her RMR.
These handhelds can be found at gyms and less commonly at doctor's offices. After a trainer or doctor obtains a person's RMR results from the handheld, the trainer or doctor estimates the user's daily activity levels and calorie intake levels to come up with a tailored fitness plan. In addition, some handhelds compare a person's RMR to the average RMR to measure if that person's metabolism is slower, faster or the same as an average person with the same height, weight and age.
For people without access to or the need for advanced equipment that can measure metabolism, an easier and less expensive way to measure metabolism is to calculate it with a standardized formula. These formulas measure height, weight and age to come up with a RMR. They are for the average person with a standard height, weight and age, so the formulas are less accurate than other methods.
One of these formulas is the Harris-Benedict equation. Men should compute their RMR with this formula: 66 + (13.7 x weight in kilograms) + (5 x height in centimeters) - (6.8 x age in years). Women should use this formula: 655 + (9.6 x weight in kilograms) + (1.8 x height in centimeters) - (4.7 x age in years). Research has shown that the Harris-Benedict equation is less accurate for overweight people and people who have lost weight than it is for people who have an average weight and have never been overweight.
The Harris-Benedict equation can be used as a weight loss tool. After finding his or her RMR, a person can add this to the calories he or she expends doing daily activities. By figuring out the calories expended in a day, a person can aim to eat fewer calories than this number in order to lose weight.