BASAL METABOLIC RATE (BMR): WHAT DOES IT MEAN?
BMR is but 1 of the 3 facets that encompasses your TDEE
Total Daily Energy Expenditure, or total “calories burned” in a day, has three major components: basal or resting metabolic rate, the thermic effect of food (calories expended through digestion) and the energy cost of physical activity. Having a general understanding of your daily energy expenditure is a GREAT place to start to understand weight maintenance and loss. Once you understand how many calories your body expends just to maintain vital functions, you can then better understand weight loss in terms of how many calories you should subtract from your diet to lose weight, and/ or how much activity you should engage in to engage in a target calorie deficit (“burn calories”). This article will help you to understand those concepts and apply them to yourself with evidence-based equations provided.
Imagine you laid in bed all day. You didn’t get up to eat, go to the bathroom, or even to change the channel from that rerun of Friends you have seen 84 times already. If you were to measure how many calories (energy) your body expended just to maintain this level of ultimate couch potato, you would get your basal metabolic rate (BMR), also known as resting energy expenditure (REE) or resting metabolic rate (BMR). For the sake of this article, we will continue to reference “BMR” as our standard.
The MOST accurate way to measure BMR is with is a portable indirect calorimeter, which is accurate to within 5% of your true BMR. HOWEVER, those are only used clinically, as they are costly and require trained personnel. Because those are so unavailable, we need reliable and accessible predictive equations instead.
BMR: How Do You Find It?
Mifflin St. Jeor Equation:
A systematic review done by the (American Dietetic Association) compared four of the most commonly used equations to estimate BMR, including the Harris-Benedict, Mifflin-St Jeor, Owen, and WHO/FAO/UNU). When they compared these equations, the Mifflin-St Jeor equation was the most reliable equation, as it consistently predicted BMR within 10% of that measured with indirect calorimetry, and it also had the narrowest error range (meaning it was less likely that a measurement obtained was due to some kind of examiner/ participant error, etc).1
NOTE: The populations studied were “healthy,” non- obese and obese populations. This study did not include those with a disease that might have impact on BMR, such as thyroid disease or diabetes mellitus, and were not taking medications known to affect BMR. Therefore, while this is the most reliable equation for a “healthy” person, keep in mind that the results of this study and the reliability of the equation cannot be applied to those with metabolic diseases, and those individuals can only have their BMR more accurately measured in laboratory, performed by a physician .1
This equation basically gives you a rough estimate of how many calories your body “burns” in a resting state, and accounts for about 70% of your total daily energy expenditure. Technically, taking your height, weight, age and gender into account, you would be able to maintain your weight while consuming this amount of calories each day, without any additional activity. It does not tell you how many calories to consume for weight loss purposes.
METRIC: 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) - 161.
ENGLISH: 10 x (2.02) lbs +6.25 x (0.39 x height in inches) -5 x age (years) – 161\
METRIC: 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) + 5
ENGLISH:10x (2.02) lbs + 6.25 x (0.39 x height in inches) – 5 x age (years) + 5
We put together a convenient BMR calculator for you, so you can just plug in the numbers and let us do the math:
The Harris- Benedict Equation for BMR
Most of us have seen this equation. Usually, when you use an online calculator to find your BMR, this is the equation you are actually plugging your information into. Like the equation listed above, this Harris-Benedict Equation is usually used to estimate BMR. The equations were published in 1919, and they have been commonly used for years. However, a study in 1990 found that this equation overestimated measured BMR by about 5% when compared to more precise indirect calorimetry. That could mean the difference of 100 extra calories for a calculated 2,000 calorie RMR.
This was the older formula (1919):
BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age in years )
BMR = 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height in inches ) - ( 6.8 x age in year )
The Harris- Benedict equation was revisited in 1984, and may be more accurate for obese individuals. 2
Here is the newer, revised formula (1984): *Put these equations in faded blue boxes grouped by gender*
METRIC: 447.593 + ( 9.247 x weight in kg ) + ( 3.098 x height in cm ) - (4.330 x age in years )
ENGLISH: 447.593 + ( 4.20 x weight in lbs ) + ( 7.9 x height in inches) - (4.330 x age in years )
METRIC: 88.362 + ( 13.397 x weight in kg ) + ( 4.799 x height in cm ) - ( 5.677 x age in years )
ENGLISH: 88.362 + ( 6.08 x weight in lbs ) + ( 12.28 x height in inches ) - ( 5.677 x age in years )
*Note: This equation is not reliable in malnourished populations, according to the results of the study.2\
TDEE: Total Daily Energy Expenditure:
Now that you have identified your BMR, you probably want to find out about how many calories you expend in an average day, rather than during an ultimate coach potato marathon. Our RMR calculator for the Mifflin St. Jeor equation has already crunched the numbers and done this for you! Again, this is an equation to help you understand how many calories you expend (“burn calories”) as you go about your day; it does not give you any information about weight loss. According to the equation, if you continue to eat the amount of calories given, you will maintain your current weight.
This is how we calculated your TDEE: As a general rule of thumb, you can use your RMR calculation, and plug it into one of the following Harris-Benedict formulas corresponding with your activity level.
- If you are sedentary (little or no exercise) : BMR x 1.2 = TDEE
- If you are lightly active (light exercise/sports 1-3 days/week) : BMR x 1.375 = TDEE
- If you are moderatetely active (moderate exercise/sports 3-5 days/week): BMR x 1.55 = TDEE
- If you are very active (hard exercise/sports 6-7 days a week): BMR x 1.725 = TDEE
- If you are extra active (very hard exercise/sports & physical job or 2x training): = BMR x 1.9 = TDEE
Author’s note for using this BMR equation:
RMR, or resting metabolic rate, is synonymous (means the same thing) with BMR.
A predictive equation for BMR should be within 10% of the actual measured value via calorimetry.
Though metabolic equations each have inaccuracies, the Mifflin- St. Jeor equation has been found to have the best accuracy (within 10% of calorimetric measurements) in adults without metabolic disease across the lifespan. This equation is less accurate in obese adults.
Basically, DO regard it as an appropriate, well supported estimate of your BMR if you fall under this category, but if you have a metabolic disease, or considered obese (research considers BMI >30 to be obese, but this does not account for the heavier folks with lots of dense muscle mass), be aware that the equation is less accurate (accurate 40% of the time).
The most accurate way to calculate your BMR is to find a place near you that measures it via metabolic testing (within 5% of actual when performed by a trained professional). Metabolic testing will give you BMR and VO2 max values, to ultimately provide you with personalized heart rate training zones, and tell you how many and what type of calories (carbs or fat) you’re burning within those zones.
This is one example of a facility that may have providers near you: http://korr.com/facility-finder/ Isolator Fitness is not affiliated with this organization, but I recently listened to a very knowledgeable lecturer at a national physical therapy conference who spoke highly of the company, and he has been using the equipment for 5 years with great success.
FYI, Here are 3 studies to elaborate on aforementioned claims of the Mifflin equation’s use in non- obese vs. obese adult populations:
Non- obese adults without metabolic/ endocrine disease: “The Mifflin St. Jeor equation is confirmed as a useful prediction equation for resting metabolic rate in community-living ambulatory adults of various body sizes... Accuracy rate is lower in obese than non-obese people,” and so future research lends itself to establishing and validating an obesity-specific equation. (Published in 2013.)
Frankenfield D .Bias and accuracy of resting metabolic rate equations in non-obese and obese adults. Clin Nutr. 2013 Dec; 32(6):976-82. doi: 10.1016/j.clnu.2013.03.022.
Overweight and obese adults: “In our sample of overweight and obese adults, RMR prediction to within ±10% of the measured value was only accurate ∼40% of the time, regardless of gender and weight classification. In clinical weight management settings direct measures of RMR should be made wherever possible.” (Published in 2015.)
Wright T et al. Accuracy of resting metabolic rate prediction in overweight and obese Australian adults. Obes Res Clin Pract. 2015 Aug 12. doi: 10.1016/j.orcp.2015.07.008.
Older people >70 years old: “Current equations used to calculate RMR in older people have inaccuracies, although the Mifflin St-Jeor equation was most accurate.” (Published in 2015.)
Reidlinger DP1, Willis JM, Whelan K. J Hum Nutr Diet. 2015 Feb;28(1):72-84. doi: 10.1111/jhn.12215. Epub 2014 Feb 14. Resting metabolic rate and anthropometry in older people: a comparison of measured and calculated values.
1.) Frankenfield, David et al. Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults: A Systematic Review. Journal of the American Dietetic Association. 2005.
2.) Roza A. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. The American Society for Clinical Nutrition, Inc. 1984.
3.) Ravussin E. et al. Determinants of 24-hour energy expenditure in man. Methods and results using a respiratory chamber. J Clin Invest. 1986.
4.) Zurlo F et al. Spontaneous physical activity and obesity: cross-sectional and longitudinal studies in Pima Indians. Am J Physiol. 1992.
5.) Levine J et al. Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science 283. 1999.