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Fitness Testing: Part 2 | RMR Test

Updated: Jun 7, 2023

Do you know how many calories you can eat without gaining any weight? Learn more about why taking an RMR test might help you create a nutrition plan to reach your health goals.



After completing the DEXA scan discussed in Part 1 of this series, I went into the next room to start the Resting Metabolic Rate (RMR) test. Metabolic rate testing accurately measures your metabolism by analyzing your breath composition when fasted. This analysis tells you how many calories your body burns at rest and how your metabolism compares to others based on age, gender, height, and weight. You can then use these precise measurements to create a personalized nutrition plan based on your caloric needs.

The weight loss and weight management market was valued at $192.2 billion in 2019 and is projected to reach $295.3 billion by 2027[i] One principal driver of this growth is that people rarely get the results they are hoping for from their diet and exercise programs and are always searching for the next silver bullet. People, myself included, often blame the diet for their lack of results, when in reality it mostly boils down to a lack of consistency. I’ve found that this inconsistency is primarily caused by starting diets that are unsustainable and incompatible with your lifestyle. There have been many times that, after a sudden burst of motivation to lose weight, I start dieting and quickly go overboard with my efforts. In my haste to get results, I under-eat, which leads to fatigue and uncontrollable hunger. This causes me to binge, and after only a few days I end up right back where I started. My hope with taking the RMR test was to eliminate the guesswork of dieting and learn exactly how to reach my weight goals sustainably. As anyone in the nutrition field will tell you, the best diet is the one you can stick to.

A note: To ensure accurate results, this test requires being fasted for 4 hours prior, including no caffeine and no exercise. This ensures the data is based on your body in its resting state, not when it’s revved up or slowed down by any other inputs. As I understand it, this test is considered accurate to within roughly 10% for its caloric results.


The Test:

Resting Metabolic Rate (RMR) Test
RMR Test

I settled into the reclining chair, put the breathing tube in my mouth and shut both nostrils with the nose clip. The test requires having a tight seal on the tube and a fully closed nose, this ensures that 100% of your breath is processed by the machine as you inhale and exhale. Although it took some time to get comfortable, the 10-minute test was quick and straightforward. I know what you are thinking, no I did not want a selfie in here with everything on.



Before diving into my results, I want to provide a more thorough definition for the test’s three outputs, starting with Resting Metabolic Rate (RMR). Your RMR is the number of calories you would burn for essential bodily functions over the course of the day while at rest – think lazy Sunday on the couch. The breakdown of some of those functions can be seen in the graphic below. The test determines how fast your metabolism is working to sustain these essential functions by analyzing your breath composition. If you are interested in researching this topic further, you may also encounter the term Basal Metabolic Rate (BMR), which is often used interchangeably with RMR but is not exactly the same.

Resting Metabolic Rate

The second output is called Non-Exercise Activity Thermogenesis (NEAT), which is an estimate of how many calories you burn daily based on your lifestyle and activity level, a number that your test practitioner will help you determine. Your activity level is highly dependent on your day-to-day lifestyle and requires an honest assessment of what a typical day looks like for you. For example, someone who works a desk job burns less energy than a teacher who walks around all day or a construction worker doing manual labor. There are many simple ways to increase NEAT, which could include things like standing more and adding short walks into your day.

The final piece of the puzzle is the number of calories you burn during exercise. Your practitioner will help you determine this number based on your exercise frequency, duration, and intensity.


The Three Zones:

Calculating accurate numbers for your energy expenditure is critical for dieting because it allows you to understand where your three different caloric zones are, as seen in the chart on the right.

Caloric Expenditure for Weight Loss
My Specific Caloric Zones

The "maintenance zone" is where you match your input and output to maintain or surpass to gain weight.

Below the maintenance section is the "weight loss zone," or the maximum number of calories you can ingest and still lose weight, which is known as a caloric deficit.

Finally, at the bottom of the stack is the "medically supervised zone," the area in which you should only engage under the supervision of a doctor. A critical point here is that operating within this caloric zone could not only be dangerous for your health, but it could actually be counterproductive to your weight loss. When you under-nourish for extended periods, your body will eventually enter a starvation mode to protect itself. This will cause your metabolism to slow down to conserve energy, thereby lowering your RMR and making it harder to burn calories.

The guideline for losing fat is to eat below your maintenance zone but not so low that you enter the medically supervised zone. This will keep your energy levels up and your hunger manageable without slowing your metabolism, and your body will start pulling from its fat stores to make up the caloric difference. This delicate balance is difficult to strike, and utilizing general guidelines is a futile exercise given the highly personal nature of the inputs discussed above.


The Results:

Caloric expenditure

Getting into the numbers, my RMR of 2261 calories is higher than anticipated, driven by my metabolism being slightly faster than average (+6%). I have always thought of myself as someone with a slow metabolism, but this increase above baseline is likely due to my above-average amount of muscle mass for my height (as determined by the DEXA Scan).

Faster Metabolism

The number notated above my RMR was added by Jessica, the technician at Live Lean RX, based on my daily activity level, adding 678 more calories onto the stack. Finally, at the top of the chart is my caloric burn during exercise, which is 282 calories. Jessica kept this estimate on the lower side for me to make the total estimate conservative. Combining all of these elements puts me at a total of 3221 calories burned in an average day.

Knowing this figure allows me to build my diet plan with clarity and precision. Armed with my different zones, I plan to eat about 2300 calories a day. This amount will ensure that I don't get too hungry or risk losing muscle while still keeping me at a deficit so I can lose fat. If I want to increase my caloric deficit further, I have to earn it by increasing my daily activity and exercise, not by starving myself. In practice, this will take the form of standing more while I work and taking short walks in the morning and after meals. For exercise, it means adding some additional steady-state cardio on top of my regular routine to increase my expenditure and add to the calorie deficit.

The other invaluable insight that the RMR test provided was the mix of carbs and fat that my body was burning at the test time: 47% carbs and 53% fat. There is a concept in nutrition called Metabolic Flexibility, which refers to your body's ability to burn various types of fuel for energy, namely carbs and fat. If you aren't metabolically flexible, you cannot efficiently burn different types of fuel. In most people, this means not burning fat. If the body cannot burn fat well, then it will be much harder to lose weight. In this case, specialized techniques like fasting or diets like Keto might be necessary to help the body become fat-adapted. Thankfully, I have a nice balance of the two, and with more energy output (calories burned), my body should be able to pull from its fat stores for energy.

A note: Several variables can affect this energy mix ratio, including your food composition from the day before. Given I fasted overnight, I feel reasonably confident in the accuracy of the results. Click here for a primer on metabolic flexibility, and click here for more information on becoming fat-adapted.



Out of the three tests – DEXA, RMR, and VO2 Max – I think RMR will provide the most actionable information for every person who takes it. Weight management is an absolutely critical part of health and longevity, whether you’re trying to lose fat, gain muscle, or just stay where you are, knowing your numbers eliminates the guess work. Understanding your RMR is a cornerstone piece to the nutrition puzzle.

Additionally, having a better understanding of your metabolic flexibility will allow you to choose a diet that is optimized for your body and enables lasting change. At an average cost of around $100, this non-invasive test is worth every penny, and I recommend it for everyone looking to dial in their health and performance.



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