than the one discussed in this post.
As you may know, I’ve been very fortunate to have had the opportunity to visit the Mayo Clinic Bariatric Center in Jacksonville, Florida. While there, they performed many tests, including my resting energy expenditure (REE) and basal metabolic rate (BMR). These terms are sometimes used interchangeably though there are slight differences. REE includes some low effort activities like eating and using the bathroom (1).
BMR is the amount of calories used while lying still but awake before rising in the morning (2).
Luckily for me, the higher result was from the more accurate test, True One Canopy indirect calorimetry. It found that my REE was 1,856 calories per day for a weight of 183 pounds. This fasting test measures the gasses exhaled while the patient breathes into a mask connected to the True One Canopy for 10 minutes.
Indirect calorimetry is the science associated with analysing metabolic processes. While direct calorimetry is achieved through direct measurement of total body heat produced, such as via a thermally sealed chamber, indirect calorimetry measures respiratory gases, i.e. oxygen (O2) and carbon dioxide (CO2) that are influenced by metabolism to meet energy requirements (4).
The other test used a top of the line Seca scale (3). It provided a lot of information, including a BMR. But devices like this do not have the accuracy of indirect calorimeter (5). Although the Seca scale has more data to improve the quality of its calculations, it’s still just that – a calculation.
The two tests were performed in a clinical setting, but I was told that one of the methods was much more accurate, so that’s the one they used when making dietary recommendations. This made me wonder about the accuracy of the more commonly used on-line calculators that many dieters use for planning purposes.
What exactly is the calculation for BMR? There are multiple methods, but one given on the verywellfit website is the Harris-Benedict Equation (6):
- Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)
- Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)
Testing this out, I inputted my old weight information and got a result of 1,478 using this BMR calculator: https://www.omnicalculator.com/health/bmr-harris-benedict-equation (The verywellfit calculator was down at the time of writing.) This is very similar to the output of the Seca scale.
I then visited 5 additional websites with similar results ranging from 1,428 to 1,480. See footnotes 7 – 11 if you’d like to give this a try. They did not specify which equation(s) were used.
As a point of interest, I had great difficulty finding an accurate REE calculator. One that I tested was off by 50%. (I’m able to confirm this because I know my REE from indirect calorimetry.) Upon further reading, I realized that this may be the nature of REE calculations. In a hospital study that used 15 different equations, “The percentage of accurate predicted REE was low in all equations, ranging from 8 to 49%” (12). For this reason, it may be better to use a BMR calculator.
What can account for the differences in calculated BMR and the actual calories burned at rest, in addition to age, sex, height, and weight? Body composition is a factor, with lean tissue like muscle using more calories than adipose tissue (2). Inherited factors can also play a role as well as can some health conditions.
If you are wondering how my Mayo dietitian used REE in my case, it was pretty simple. Basically, I was instructed to eat 1,800 calories (just under my REE) if I exercised. On days that I did not exercise, I was to cut this by about 400 calories. This resulted in a 500 calorie deficit daily or a pound loss weekly. That calculation held true until I reached my first goal weight. At this point to lose more weight I would have to exercise more. I’m unwilling to eat less!
Both BMR and REE can be used to calculate the calories needed for weight maintenance. Use these numbers as a baseline and then adjust with exercise or caloric changes to zero in on your exact needs. Check your scale to confirm your progress.
Interested in knowing how often to weigh in? See this post: https://lindawbrowning.com/2023/02/22/weighing-in-on-that/
What factors can we change so that our bodies burn more fuel at rest? The most obvious is to increase our muscle mass. Exercise is particularly helpful because it burns calories in the activity itself and then continues to give you the added boost of additional muscle mass. Adding strength building exercise to your plans will help you maintain a healthy weight.
(1). https://www.webmd.com/fitness-exercise/difference-between-bmr-and-rmr
(2). https://www.sciencedirect.com/topics/medicine-and-dentistry/basal-metabolic-rate
(3). https://www.indirectcalorimetry.net/understanding-indirect-calorimetry/
(5). https://www.sciencedirect.com/science/article/pii/S2667268521000048
(6). https://www.verywellfit.com/what-is-bmr-or-basal-metabolic-rate-3495380
(8). https://www.active.com/fitness/calculators/bmr
(9). https://www.bodybuilding.com/fun/bmr_calculator.htm
(10). https://www.myfitnesspal.com/tools/bmr-calculator
(11). https://www.bmrcalculator.org/
(12). https://nutritionandmetabolism.biomedcentral.com/articles/10.1186/s12986-016-0145-3
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