What is RMR and How Do We Measure It?

What is the difference between resting metabolic rate (RMR) and basal metabolic rate (BMR)? 

According to Healthline.com: 

“Basal metabolic rate (BMR) is often used interchangeably with resting metabolic rate (RMR). While BMR is a minimum number of calories required for basic functions at rest, RMR — also called resting energy expenditure (REE) — is the number of calories that your body burns while it’s at rest.

Although BMR and RMR slightly differ from each other, your RMR should be an accurate estimate of your BMR.”

According to:

Source: Modern Nutrition in Health and Disease, Shils ME, 10th ed. 2006 page 141.

“RMR is defined by calorimetry (almost always using indirect spirometry) in a resting comfortable position, awake, following at least a 3-4 hr fast. Prior exercise restriction is not required but is highly advisable. REE is ordinarily a 24 hr extrapolation of RMR. RMR kcal/min X 1440 min/day.

BMR is conducted in a supine position, while awake and motionless, in the post-absorptive state following a 12 hr fast overnight.

Sleeping metabolic rate is measured in a sleeping state. Few published protocols exist but assume the same restrictions for BMR.”

We at Breathe Performance utilize the RMR number for its convenience to measure when compared to BMR. 

In other words, RMR is slightly higher than your BMR because it includes some of the stresses of the day from the day in which you measure it. BMR measures a completely resting body and typically is measured over an hour and a half and only uses the last half hour of data. A very time-consuming ordeal. RMR can be measured with relative accuracy inside of 30 minutes. 

Why do we want to know this number?

Knowing this number allows us to begin the process of nutrition or lifestyle adjustments needed to get you closer to your goal. Through manipulation of our diet we can lose, maintain, or add body weight based off of a calories-in/calories-out model. 

Lose = Calorie deficit

Gain = Calorie surplus

Maintain = Calories equal to outgoing energy.

There are many factors in your metabolisms’ measurement including but not limited to;

• Age
• Sex
• Race
• Diet
• History
• Body type
• Stress
• Breath
• Drug use (prescribed or otherwise)
• Genetic and epigenetic expression 
• Temperature
• Humidity
• Air quality
• Many more…

There are formulas that try to estimate your BMR such as the Harris-Benedict formula. They are often very inaccurate when compared to indirect calorimetry which is the method we at Breathe Performance utilize using our PNOĒ units.

The method known as indirect calorimetry  involves collecting the gases you expire from your nose or mouth, funneling those gases through a tube to an analyzer in a metabolic cart, and calculating the number of calories you are burning based on principles of metabolism. This method is a cornerstone of exercise physiology classes at academic institutions while being utilized in medical facilities and Olympic training centers.

Another reason we utilize indirect calorimetry is the ability to identify fuel utilization at rest, helping us to identify unnecessary carb utilization at rest. 

We argue that metabolic efficiency can be developed as the overarching goal helping the body achieve homeostasis through diet and fitness, reducing global inflammation and improving overall function of the human.

The amount of energy stored in the form of fat is large, representing 92-98% of all endogenously stored energy with CHO contributing only about 2-8%. Fat is at the bottom of an oxidative hierarchy that determines fuel selection, and its oxidation is governed by the presence or absence of the other macronutrients. In addition, the rate at which it can be oxidized depends on the intensity of energy expenditure. Once you pass your anaerobic threshold all calories expended will be from carbohydrates, either from the bloodstream or from the muscles and/or liver. We prefer to utilize these limited calorie sources for when it is necessary rather than just when it is convenient. Just like in life, carbohydrates are always convenient inside of the body too.