BASAL METABOLIC RATE - BMR
BMR introduction
Basal Metabolic Rate (BMR) represents the amount of energy your body needs to keep you alive while at complete rest in a neutral temperature environment and with an inactive digestive system.
Think of it like measuring how much fuel a parked car consumes while the engine is idling—your body also uses energy to maintain essential functions even when you’re not moving.
These vital functions include the activity of the heart, brain, kidneys, nervous system, liver, lungs, intestines, skin, and muscles. For most people, BMR accounts for roughly 70% of the total calories burned daily.
Physical activity contributes about 20%, while another 10% is used for digesting food (known as the thermic effect of food).
Measuring BMR directly requires very strict conditions: the person must be awake, completely rested, and with minimal activation of the sympathetic nervous system. Because this is difficult outside of a clinical setting, BMR is typically estimated using scientific equations.
On this website, we use the Mifflin–St Jeor Equation, considered the most accurate formula since its introduction in 1990.
Mifflin–St Jeor Equation (Used in The Calculator above)
For men:
BMR = 10W + 6.25H – 5A + 5
For women:
BMR = 10W + 6.25H – 5A – 161
Where:
W = weight (kg)
H = height (cm)
A = age (years)
This BMR value is then multiplied by an activity factor (1.2–1.9) to estimate daily caloric needs.
Factors That Influence BMR
Muscle Mass
Anaerobic exercises (such as weight training) increase muscle mass, which boosts BMR because muscle tissue requires more energy at rest. Aerobic exercise alone does not significantly raise BMR.
Age
BMR generally decreases with age due to muscle mass loss and physiological changes.
Genetics
Inherited traits can affect metabolic rate.
Climate
Cold environments increase BMR as the body works to produce heat. Very hot climates can also raise BMR as the body cools itself.
A 1.36°F increase in internal temperature raises BMR by about 7%.
Diet
Frequent smaller meals can slightly increase BMR.
Long-term starvation significantly reduces BMR—up to 30%—as the body conserves energy, similar to a phone entering power-saving mode.
Pregnancy & Hormonal Changes
Pregnancy increases calorie needs to support the developing fetus. Hormonal changes during menopause may also affect BMR.
Supplements
Some substances, such as caffeine or certain weight-loss supplements, can temporarily increase BMR.
BMR Tests Accuracy
While online calculators provide helpful estimates, they are not perfect.
The most accurate BMR measurements come from calorimetry devices found in medical centers, sports clubs, and weight-loss clinics.
Limitations of BMR !
A 2005 meta-analysis found that even when all known metabolic factors are controlled, about 26% of BMR variation remains unexplained.
This means individual differences still exist that science cannot fully predict.
Therefore, all BMR formulas—no matter how advanced—are still approximations, not exact measurements. The best approach is to use BMR as a starting point, track progress, and adjust nutrition and activity levels over time.
