Is resting metabolic rate (RMR) the same as basal metabolic rate (BMR)?

RMR is Not the Same as BMR

RMR (resting metabolic rate) is approximately 10% higher than BMR (basal metabolic rate), though the terms are often used interchangeably in clinical practice. 1, 2

Key Differences in Measurement Conditions

BMR Measurement Requirements

BMR represents the minimal energy expenditure compatible with life and requires strictly controlled laboratory conditions 2:

• Measured in a recumbent position
• Thermo-neutral environment
• After 12-18 hours of fasting
• Immediately upon awakening before any daily activities begin
• No physical activity

RMR Measurement Requirements

RMR is measured under less stringent conditions 1:

• Can be measured at any resting state throughout the day
• Requires only 4 hours of fasting (not 12-18 hours)
• Patient should be seated and rested for 10 minutes prior to testing
• No intense physical activity for 4 hours before measurement
• No tobacco use for 1 hour before testing

The 10% Difference in Clinical Practice

The consistent finding across multiple guidelines is that RMR measures approximately 10% higher than BMR 1, 2. This difference exists because:

• RMR includes slightly more metabolic activity than the absolute basal state
• Measurements occur under less controlled conditions
• Some residual effects of recent food intake or activity may persist

Clinical Application

In practical metabolic calculations, this 10% difference is actually built into standard formulas. When calculating total energy expenditure (TEE):

• Using BMR: TEE = BMR × physical activity level (PAL) × 1.1 (for thermogenesis)
• Using RMR: TEE = RMR × PAL (the 10% for thermogenesis is already included in the RMR value) 1

For sedentary individuals: TEE = RMR × 1.2 1

For active individuals: TEE = RMR × 1.6 1

Important Clinical Caveats

While the terms are often used interchangeably in clinical settings, understanding the distinction matters when:

1. Comparing measured values to predicted equations - Most prediction equations (Harris-Benedict, Mifflin-St Jeor) estimate RMR, not true BMR 3, 4

2. Interpreting indirect calorimetry results - Office-based measurements typically yield RMR/REE values, which are 10% above basal energy expenditure 1

3. Calculating energy prescriptions - The 10% difference must be accounted for to avoid overfeeding or underfeeding 1

The pediatric guidelines 2 emphasize that REE (resting energy expenditure) does not differ by more than 10% from BMR, confirming this relationship holds across age groups.