BMR (Basal Metabolic Rate)
body-metricThe number of calories your body burns at rest to maintain vital functions like breathing, circulation, and cell production.
Definition
The number of calories your body burns at rest to maintain vital functions like breathing, circulation, and cell production. Typically accounts for 60-75% of total daily energy expenditure.
What Is Basal Metabolic Rate?
Basal Metabolic Rate (BMR) is the number of calories your body requires to maintain basic physiological functions while at complete rest — breathing, circulation, cell production, temperature regulation, and organ function. It represents the minimum energy expenditure needed to keep you alive and accounts for roughly 60–75% of total daily calorie burn in sedentary individuals.
BMR is measured under strict laboratory conditions: after a full night of sleep, in a thermoneutral environment, and at least 12 hours after eating. These conditions ensure that digestion, physical activity, and environmental stress do not influence the measurement.
How BMR Is Calculated
The two most widely used formulas for estimating BMR are the Mifflin–St Jeor equation and the Harris–Benedict equation. Mifflin–St Jeor is considered more accurate for most modern populations:
- Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
- Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
Factors that directly influence BMR include body composition (more muscle raises BMR), age (BMR declines roughly 1–2% per decade after age 20), sex, genetics, and thyroid hormone levels. Lean body mass is the strongest determinant — muscle tissue is metabolically more active than fat tissue.
Why BMR Matters for Nutrition
Understanding your BMR provides a baseline for setting calorie targets. Eating below BMR for extended periods can trigger adaptive thermogenesis — the body's mechanism to reduce energy expenditure in response to caloric restriction — making sustained weight loss more difficult. Clinicians use BMR estimates to plan enteral nutrition for hospitalized patients and to identify metabolic disorders such as hypothyroidism, which significantly suppresses basal calorie burn. For healthy individuals, BMR is the foundation on which Total Daily Energy Expenditure (TDEE) is built.
Related Guides
Understanding Calories: Energy In vs Energy Out
The science of calories — how your body uses energy and what determines your daily calorie needs.
Calorie Deficit: How Much to Lose Weight
The science of calorie deficit — how to calculate yours, safe rates of loss, and common pitfalls.
Understanding Metabolism: BMR and TDEE
How your metabolism works, what BMR and TDEE mean, and factors that affect your metabolic rate.
Reverse Dieting: How to Increase Calories Without Gaining Fat
The evidence-based strategy of slowly increasing calories after a diet to restore metabolism without fat regain.
Sleep and Weight: How Poor Sleep Sabotages Weight Loss
The hormonal mechanisms linking sleep deprivation to weight gain — ghrelin, cortisol, and metabolic disruption.
Related Terms
Metabolic Adaptation
The body's physiological response to caloric restriction: reduced TDEE through lower BMR, reduced NEAT, and hormonal changes (lower leptin, higher ghrelin).
TDEE (Total Daily Energy Expenditure)
The total number of calories you burn per day, including BMR, physical activity, and the thermic effect of food.
Lean Body Mass (LBM)
Total body weight minus fat mass, including muscle, bone, organs, and water.
Resting Metabolic Rate (RMR)
The calories burned at rest, similar to BMR but measured under less strict conditions (no overnight fast required).