Resting Metabolic Rate

Resting metabolic rate (RMR) is the number of calories your body burns at rest to maintain basic physiological functions — including breathing, circulating blood, regulating body temperature, maintaining organ function, and supporting cellular repair. RMR accounts for approximately 60-75% of total daily energy expenditure, making it by far the largest component of your calorie burn. The remaining energy expenditure comes from physical activity (15-30%) and the thermic effect of food (approximately 10%).

RMR is closely related to but slightly different from basal metabolic rate (BMR). BMR is measured under strict conditions — after an overnight fast, in a temperature-controlled room, upon waking. RMR is measured under slightly less restrictive conditions and is typically 10-20% higher than BMR. In practice, the terms are often used interchangeably.

The primary determinants of RMR include lean body mass (muscle tissue is more metabolically active than fat), body size (larger bodies have higher RMR), age (RMR declines approximately 1-2% per decade), sex (males typically have higher RMR due to greater muscle mass), thyroid function, and genetics. Understanding RMR is valuable for weight management, as it provides a baseline for calculating total caloric needs.

Understanding your RMR is valuable for developing realistic weight management strategies. If you've struggled with weight loss despite calorie restriction, your RMR may have adapted downward. Indirect calorimetry testing, available at many medical and fitness facilities, can provide your actual RMR rather than relying on potentially inaccurate estimation formulas.

The most effective strategy for maintaining or increasing RMR is building and preserving lean muscle mass through resistance training — particularly important as you age. Adequate protein intake, consistent meal timing (avoiding prolonged severe restriction), quality sleep, and thyroid health all support optimal RMR.