Basal metabolic rate measurements are taken immediately following eight hours of sleep.
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In order to maintain your weight, the calories you consume must equal the calories you burn. You can easily estimate the number of calories you eat using food labels, but determining the number of calories you burn is a little more difficult. Although the terms are often used interchangeably, basal metabolic rate and resting metabolic rate are two different techniques used to estimate energy requirements to maintain basic body functions.
Both BMR, and RMR, estimate the number of calories you burn at rest, but RMR takes additional factors into consideration when determining needs. BMR measures your basal energy expenditure, or BEE. The BEE is a 24 hour estimation of the number of calories you burn maintaining your most basic bodily functions, such as breathing, circulating blood and growing and repairing cells. RMR measures your resting energy expenditure. REE determines the number of calories you burn in a 24 hour period maintaining basic bodily functions, but also includes the number of calories burned eating and conducting small amounts of activity.
How It's Measured
Measurement of BMR is more restrictive than RMR. Measuring BMR requires a clinical procedure that takes place in a hospital or laboratory and requires the subject to spend the night. BMR is taken first thing in the morning, after eight hours of sleep and a 12 hour fast while the subject is lying down. RMR does not require a sleepover, and is measured at any time of day following a three to four hour fast. Both use indirect calorimetry to determine needs. Indirect calorimetry measures the amount of oxygen consumed and carbon dioxide produced by the body during a specified period of time.
Difference in Calorie Estimation
When comparing calorie estimations, RMR is slightly higher than BMR, but the difference is less than 10 percent, according to the National Research Council. While both RMR and BMR are considered estimations of your calorie needs, BMR is a more accurate measure because of the stricter procedures required to obtain it.
Making it Work For You
Online calorie calculators are a great start -- but at the end of the day, you're a real person with a unique lifestyle, body composition and genetic makeup, not a set of numbers plugged into a calculator. Online calculators offer a one-size-fits-all answer that estimates your calorie burn, but your individual burn might deviate slightly higher or lower. Watch your weight over time and adjust your calorie intake accordingly until you reach your goals.