Weight Loss & Metabolic Health
What Is Resting Metabolic Rate?
Last reviewed: May 2026 · Haute MD Editorial Team
Resting metabolic rate (RMR) is the number of calories the body burns at rest to maintain basic physiological functions — breathing, circulation, temperature regulation, organ activity. It typically accounts for 60–70% of total daily energy expenditure and is determined primarily by lean body mass, age, sex, and hormonal status. RMR can be measured (indirect calorimetry) or estimated (Mifflin-St Jeor and other equations).
What determines RMR
Muscle is the most metabolically active tissue at rest, so lean body mass is the single largest determinant of RMR. Men generally have higher RMRs than women due to higher muscle mass; RMR declines roughly 1–2% per decade after age 30, primarily because of muscle loss. Thyroid hormone sets the metabolic 'thermostat' — even subclinical hypothyroidism can reduce RMR by 5–15%. Caloric restriction lowers RMR via adaptive thermogenesis, which is why crash diets backfire.
How RMR is measured
The gold standard is indirect calorimetry — a 15–30 minute test measuring oxygen consumption and carbon dioxide production at rest. Available at many longevity, sports medicine, and concierge practices, it typically costs $100–200 and provides a personalized number rather than an estimate. Equations like Mifflin-St Jeor are reasonable starting points; DEXA-derived RMR estimates from lean mass are more accurate than equations alone.
How to protect and grow RMR
Resistance training is the single most effective intervention — every pound of added muscle adds roughly 6–10 calories per day to RMR (modest individually, meaningful cumulatively, plus the much larger effect of training itself). Adequate protein supports muscle. Avoiding chronic aggressive restriction, sleeping 7–9 hours, treating thyroid and hormonal deficiencies, and managing stress all preserve RMR. After a weight loss phase, a 1–2 week diet break at maintenance helps restore RMR before resuming a deficit.
Frequently Asked Questions
Can I increase my metabolic rate?
Yes, modestly but meaningfully — primarily by building muscle through resistance training. Combined with NEAT increases, the practical metabolic gain can be several hundred calories per day.
Does cold exposure increase metabolism?
Brief cold exposure activates brown fat and modestly increases energy expenditure. The effect is real but small relative to muscle and NEAT.
Why is my RMR lower than predicted?
Possible reasons include lower lean mass than expected, history of repeated dieting, hypothyroidism, low caloric intake, sleep loss, or chronic stress. Measurement clarifies the question.
How does aging affect RMR?
RMR falls about 1–2% per decade after 30, mostly due to muscle loss. Lifelong resistance training largely prevents this decline.
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