Your BMR represents the basal level of energy the body requires to support vital organs like the heart, brain, lungs, liver, muscles, skin, intestines, and sex organs when the digestive system is inactive. Even while parked like a car, the body still consumes calories to keep these organs working. This quiet but essential metabolism often accounts for about ~70% of total energy, with physical activity adding another ~20%, and digestion or thermogenesis contributing around ~10%.
An accurate measurement of BMR value can only be achieved under restrictive circumstances, ensuring the sympathetic nervous system stays inactive. These conditions reveal the body’s true caloric needs, forming the largest component of daily energy expenditure. Depending on lifestyle, multipliers like 1.2 to 1.9 are applied to estimate total caloric needs and overall caloric need.
Over time, several formula approaches have been introduced and later revised. The Harris-Benedict Equation (updated in 1984) was widely used until the Mifflin-St Jeor Equation came in 1990. Today, the Mifflin-St Jeor is often considered more accurate, while the Katch-McArdle Formula calculates resting daily energy (RDEE) by factoring in lean body mass and body fat, making it effective for those who are leaner. In practice, each method relies on statistical data but adapts to real-world needs through expanded settings.
