RMR

RMR, or resting metabolic rate, is the amount of energy the body requires to maintain basic physiological functions while at rest. It represents the largest component of daily energy expenditure for many people and varies with body composition, particularly lean muscle mass, as well as age and sex.

Measurement and estimation commonly used. In practice, RMR is measured by indirect calorimetry, which estimates energy use from oxygen consumption and carbon dioxide production after a period of rest and an overnight fast. Direct calorimetry is rare and specialized. When measurement is not available, RMR is estimated with predictive equations such as the Mifflin-St Jeor or Harris-Benedict formulas, using inputs for age, sex, height, and weight. RMR is typically reported in kilocalories per day (kcal/day) or kilojoules per day (kJ/day).

Factors influencing RMR. RMR varies with age, sex, and especially lean body mass. Hormonal status (notably thyroid hormones), sleep, fasting, temperature, and nutritional state also affect it. Physical training can increase lean mass and thereby elevate RMR modestly. Genetics, illness, and certain medications can alter resting energy needs.

Applications. RMR is used in clinical nutrition and weight-management planning to estimate total daily energy expenditure when combined with activity factors to determine caloric needs. It informs dietary prescriptions for weight loss, gain, or maintenance, and supports medical assessments of metabolic health.

Relation to BMR and TDEE. BMR refers to energy expenditure under strict conditions of rest after an overnight fast; RMR is measured under less stringent conditions and is typically similar or slightly higher than BMR. Total daily energy expenditure (TDEE) combines RMR with energy expended through physical activity and thermogenesis.