BMR

Basal metabolic rate (BMR) is the minimum amount of energy that a person needs to maintain basic physiological functions while at rest in a neutrally temperate environment, after a post-absorptive state (usually overnight fasting). It reflects the energy required for functions such as maintaining heartbeat, breathing, brain activity, and cellular processes.

Measurement and estimation methods vary. Direct measurement uses calorimetry, but most estimates rely on predictive equations. Common formulas include Mifflin-St Jeor, Harris-Benedict, and Cunningham. For Mifflin-St Jeor, BMR is calculated as follows: for men, 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5; for women, 10 × weight − 6.25 × height − 5 × age − 161. Harris-Benedict estimates differ slightly by sex. Cunningham uses lean body mass: BMR ≈ 500 + 22 × LBM(kg). Predictive equations vary in accuracy, especially across age groups, body compositions, and ethnicities.

BMR is distinct from resting metabolic rate (RMR), which is measured under less stringent conditions and typically yields a somewhat higher value. BMR plus additional energy expended through activity and digestion constitutes total daily energy expenditure (TDEE).

Factors influencing BMR include age, sex, body composition (lean mass), genetics, hormones, fever or illness, sleep, and temperature. Exercise and training can increase lean mass and thus BMR over time. BMR is widely used in nutrition planning, clinical assessment, and research to estimate energy needs and to understand metabolic health.