What is BMR?

The basal metabolic rate (BMR) is the energy needed while at rest in a temperature environment when the digestive system is inactive. It’s like calculating the amount of gas a car uses while left running in the driveway. In this condition, only enough energy is utilized so that the vital organs, such as the heart, brain, kidneys, nervous system, intestines, liver, lungs, sex organs, muscles, and skin, etc., are supported. A majority of (I believe 70-80% is a decent estimate of the) total energy we burn per day is the act of maintenance. Physical activity accounts for 20% of expenditure, and ~10% is utilized for diet-induced thermogenesis.

The BMR is tested under the strictest conditions, during haking hours. BMR measurement requires a state of metabolic equilibrium in which the subject’s sympathetic nervous system is inactive (i.e., the subject must be at total rest). BMR is generally the largest portion of a person’s total caloric requirement. Daily caloric requirement is the BMR multiplied by a factor ranging from 1.2 to 1.9 based on the level of physical activity.

The BMR is, for most practical purposes, derived from statistical equations based on aggregated data. The Harris-Benedict Equation is one of the oldest equations used. It was adjusted in 1984/1985 to make it more accurate and removed from use in 1990 in favor of Mifflin-St Jeor Equation. The Mifflin-St Jeor Equation is more accurate than the revised Harris-Benedict Equation. The Katch-McArdle Formula varies slightly in that it factors in body fat percentage, so it’s still not all that useful if you’re lean, which is only one point of its criticism. The Mifflin-St Jeor Equation is believed to be the most accurate equation for estimating BMR, with the exception that the Katch-McArdle Formula can be more accurate for people who are leaner and know their body fat percentage. By opening the settings, you can choose which equation you want to use for the calculation.

Below are the three equations the calculator uses:

Mifflin-St Jeor Equation:

For men:
BMR = 10W + 6.25H – 5A + 5

For women:
BMR = 10W + 6.25H – 5A – 161

Revised Harris-Benedict Equation:

For men:
BMR = 13.397W + 4.799H – 5.677A + 88.362

For women:
BMR = 9.247W + 3.098H – 4.330A + 447.593

Katch-McArdle Formula:

BMR = 370 + 21.6(1 – F)W

where:
W is body weight in kg
H is body height in cm
A is age
F is body fat in percentage

BMR Variables

Muscle Mass – Aerobic activity, such as running or cycling, has no impact on BMR. But of course, anaerobic activities such as lifting weights result in a higher BMR only indirectly, through increasing muscle mass. The physical make-up of each person’s body has an actual impact on what is technically required to keep that body going at a certain height.

Age – The older the one’s body, the lower their BMR, or the fewer number of calories necessary to maintain organ functions at a certain level.

Genetics – BMR is inherited from ancestors and is influenced by heredity.

Weather – BMR increases due to the cold energy expended to maintain body temperature in cold climates. Similarly, too much external heat may increase BMR as the body expends energy to cool internal organs. This formula is used because the BMR increases by about 7% for every 1.36 degrees Fahrenheit that the internal body temperature increases.

Diet – Small, frequent meals will raise BMR. In contrast, fasting can decrease BMR by at least 30%. However, like a “sleeping” phone that activates and turns the lights off when you touch the screen- your body is Hibernating (it’s more like a slumbering bear than a dormouse) by an vibrancy in bodily function and will give up many things, from a shallower metabolism and depressing mood to maintaining that six-pack and effective brain to squeeze more out of less energy consumed.

Pregnancy – Supporting the life of an additional fetus within increases BMR. That’s why pregnant women are always so hungry. And, on the other hand, menopause can raise or lower the BMR with hormonal variations.

Supplements – Some supplements or medications elevate BMR, primarily in the interest of weight loss. Caffeine is a common one.

BMR Tests

Online BMR Calculators with static equations are not the best way to know the BMR of a person. Ah! To put it in more easy words, if we would like to get a precise value of BMR, it would be best to ask someone who is a certified specialist, or to determine it using a calorimetry apparatus. These portable instruments are sold at numerous health and exercise clubs, in physicians’ offices, and through weight-loss centers.

Resting Metabolic Rate

There is a difference between men and man, which are commonly used interchangeably: Resting metabolic rate, or RMR, is how fast your body burns energy at rest, but not when it is completely inactive. It is also called resting energy expenditure, or REE, at times. Conditions of measurement of BMRs will have to be at a state of total physiological equilibrium, whereas RMRs are conditional and may be effectively set by the context of measurement.

Modern Wisdom

A 2005 meta-analysis study of BMR* found that even with everything we know about the factors that contribute to metabolic rate, we still don’t know 26% of the variation between people. This is, an average person should have a well-average BMR of say, but there are still methods that are not known, which set the BMR exactly.

By extension, every calculation of BMR, even by the more accurate methods done by professionals, is not accurate. The human body has not yet had all its secrets penetrated, so BMR-derived TDEE estimates are just that: estimates. BMR may help build the baseline if you’re on a path…any path about health or fitness, however, BMR can’t help more than that. An estimation of TDEE and thus BMR may give you inherrantly unsatisfactory results due to the broscience level of math that’s being applied here, however if you log your day to day workouts, diet, meals and times you did/ate, odds are you’ll get the supporting evidence of your efforts and where the issues are, what works and what doesn’t. Keeping a journal and monitoring progress and making necessary adjustments along is usually the best metric for personal goal accomplishment.