Encyclopedia entry
Resting Metabolic Rate (RMR)
Oliver Mackman · Editorial director · Best Business Loans Ltd (16833937)
Last updated 2026-05-22
Resting Metabolic Rate is the energy the body uses at complete rest, in a fasted state, at neutral temperature. It accounts for approximately 60 to 75 percent of daily energy expenditure for most adults. RMR falls during any weight-loss process, including GLP-1-driven loss; this is part of why post-loss maintenance is harder than the loss phase itself.
How RMR is measured
- · Indirect calorimetry (gold standard): measures oxygen consumption and CO2 production while the person rests for 15 to 30 minutes. UK longevity clinics including Hooke offer this.
- · Mifflin-St Jeor equation: estimates RMR from age, sex, height, weight. Off by 10 to 15 percent for any given individual but useful for population-level estimation.
- · Smartwatch estimates: rough; based on standard equations applied to wearable data.
Typical values
Adult woman, 70 kg, age 40: approximately 1,400 to 1,500 kcal/day. Adult man, 80 kg, age 40: approximately 1,700 to 1,900 kcal/day. Lean mass is the dominant driver of individual variation; muscle is metabolically active, fat (apart from brown adipose tissue) is less so. People at the same weight can have RMRs differing by 200 to 300 kcal/day based on body composition.
What RMR does during weight loss
RMR falls during weight loss for two reasons. First, the body is smaller and requires less energy to maintain. Second, an additional adaptive component (sometimes called metabolic adaptation) reduces RMR slightly more than body-size shrinkage would predict; this is the body\'s evolutionary defence against starvation. Adaptive component is typically 5 to 15 percent below predicted at the end of a loss period.
Why this matters for maintenance
A patient who lost 15 kg now has a body needing perhaps 250 to 400 kcal/day less than at start weight. Returning to pre-loss calorie intake at the lower body weight produces regain. The maintenance protocol on GLP-1 (or after GLP-1) requires recalibrating intake to the post-loss RMR plus realistic activity. This is one of the key reasons high-touch clinics emphasise the maintenance phase as much as the loss phase.
Related: sarcopenia · DXA · aftercare.