Resting Metabolic Rate (RMR) accounts for 60–75% of daily calorie expenditure. It's slightly higher than BMR because it includes the energy cost of minimal daily activity (sitting, digesting food).
RMR vs. BMR
BMR is measured under strict lab conditions (12-hour fast, complete rest). RMR is measured under less restrictive conditions and is typically 10–20% higher than BMR. For practical purposes, they're often used interchangeably.
Factors That Increase RMR
- More muscle mass (muscle burns ~6 cal/lb/day vs fat at ~2 cal/lb/day)
- Younger age
- Male sex (higher lean mass on average)
- Thyroid function
Measuring RMR Directly
Indirect calorimetry — measuring the ratio of oxygen consumed to carbon dioxide produced during rest — gives a lab-accurate RMR reading, available at some clinics and sports performance labs. It's the only way to know your actual RMR rather than a formula-based estimate, and results can differ from predicted values by 10% or more in either direction.
RMR Testing for Weight Loss Plateaus
People who've dieted repeatedly over years sometimes have a measurably lower RMR than formulas predict, due to accumulated metabolic adaptation. This is one reason unexplained weight-loss plateaus sometimes warrant an actual RMR test rather than simply cutting calories further.