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How is resting metabolic rate measured?

Resting metabolic rate (RMR) is the energy expended by an organism at rest, measured under standardized conditions. This page describes the methods used to quantify RMR in research settings and summarizes recent studies

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How is resting metabolic rate measured?

Resting metabolic rate (RMR), also called resting energy expenditure (REE), is the rate of energy utilization by an organism in a postabsorptive, thermoneutral, physically inactive state. It is typically quantified by indirect calorimetry, which calculates energy expenditure from measured oxygen consumption (VO2) and carbon dioxide production (VCO2). In research, RMR is often expressed in kilocalories per day (kcal/day) or kilojoules per day (kJ/day). The measurement requires a calibrated metabolic cart, a quiet environment, and a period of fasting and rest prior to assessment. RMR is distinguished from basal metabolic rate (BMR), which is measured under stricter conditions including awakening and before any physical activity.

RMR is a component of total daily energy expenditure (TDEE) and is influenced by body composition, particularly fat-free mass (FFM). The pathway most commonly associated with RMR regulation involves mitochondrial oxidative phosphorylation and the sirtuin family of deacetylases, particularly SIRT1 and SIRT3, which are implicated in mitochondrial biogenesis and energy expenditure [3].

Research Studies

Calcium-HMB plus vitamin D3 and resting metabolism in older adults starting semaglutide

A randomized, double-blind, placebo-controlled trial is evaluating whether daily calcium beta-hydroxy-beta-methylbutyrate (calcium-HMB) plus vitamin D3 preserves muscle mass, physical function, and resting metabolism in adults aged 65 to 85 years with type 2 diabetes who are newly starting semaglutide as part of usual clinical care. Participants receive calcium-HMB plus vitamin D3 or matching placebo for approximately 6 months. The primary outcome is change in appendicular lean mass measured by dual-energy X-ray absorptiometry (DXA) from baseline to month 6. Secondary assessments include body composition, muscle strength, physical performance, gait, physical activity, and resting metabolic rate [1].

Bimagrumab and tirzepatide: effects on body composition and resting metabolic rate

In adults with obesity, weight loss ideally consists almost exclusively of fat mass; however, loss of muscle mass and bone are unintentional consequences that may reduce resting metabolic rate and increase fall and fracture risk. A clinical trial is investigating whether bimagrumab, an investigational inhibitor of the activin type II receptor (ActRII), when combined with a glucagon-like peptide 1 receptor agonist (GLP-1 RA), can maximize fat mass loss while maintaining muscle mass. The study measures body composition, insulin sensitivity, and bone, and includes resting metabolic rate as an outcome [4].

Tirzepatide versus lifestyle intervention: impact on resting metabolic rate

A study is comparing two weight-loss strategies: one group receives a GLP-1 receptor agonist (semaglutide or tirzepatide) prescribed by their physician, while the other participates in a structured lifestyle program combining reduced-calorie diet and increased physical activity. Both groups undergo assessments at baseline and after three months, including measurement of weight, body composition, blood pressure, and resting metabolic rate [6].

Metabolic phenotyping by RMR response to fasting in obesity

A prospective, single-center, longitudinal study aims to develop a clinically applicable method for metabolic phenotyping to personalize obesity therapy in individuals with morbid obesity. The concept is that the way a person's resting metabolic rate responds to a 24-hour fast can distinguish between two phenotypes: a "thrifty" metabolism, where RMR drops significantly during fasting, potentially reducing responsiveness to conventional weight-loss interventions; and a "spendthrift" metabolism, where RMR shows little to no drop or even a slight increase, suggesting easier weight loss [8].

Energy availability and athletic performance: implications for RMR

Energy availability (EA) refers to the balance between daily energy intake and exercise energy expenditure. Low energy availability (LEA) occurs when EA is inadequate for athletic performance. LEA can suppress the reproductive system and disrupt the menstrual cycle, and it causes interrelated endocrine consequences. While this study focuses on athletic performance, the energy deficit states it describes are relevant to understanding RMR adaptations, as chronic energy deficiency can lead to metabolic suppression [7].

Dance-based exercise and metabolic health in obese breast cancer survivors

A clinical trial is evaluating whether a 3-month dance-based exercise program combined with individualized nutrition can improve health outcomes in obese breast cancer survivors in remission. The study aims to determine if the intervention reduces body weight, body fat, and visceral adiposity, and improves cardiorespiratory fitness, motor performance, gut microbiota composition, and quality of life. Resting metabolic rate is not listed as a primary outcome, but metabolic changes are assessed [5].

Artificial intelligence and determinants of food intake: relevance to RMR

A study is using artificial intelligence to analyze complex, high-dimensional data to understand why some people overeat without gaining weight while others gain weight despite not overeating. Healthy adults aged 18 to 60 years will attend 6 to 8 clinic visits over 2 years, with procedures including blood, hair, urine, and stool collection, body measurements, and DXA scans. While RMR is not explicitly mentioned in the summary, the study's focus on energy balance and body composition is related to metabolic rate assessment [2].

Sirtuin activators and weight loss: potential impact on RMR

A study is investigating sirtuin activators, particularly those targeting SIRT1 and SIRT3, for their potential to enhance metabolic flexibility and improve weight management. The sirtuin family is involved in mitochondrial biogenesis, energy expenditure, oxidative metabolism, and insulin sensitivity. Bioactive compounds that activate sirtuins, including nicotinamide riboside, are being studied for their effects on weight loss and metabolic outcomes. While RMR is not directly measured in this summary, the pathways involved are closely linked to resting energy expenditure [3].

Reference-only findings on energy expenditure and metabolic injury

A scoping review examined the effects of GLP-1 receptor agonists (mono and combination therapy) on energy expenditure. The review notes that weight loss reduces energy expenditure due to changes in body composition (fat-free mass and fat mass losses) and mass-independent adaptations (e.g., hormonal changes). GLP-1 RAs are indicated for obesity management, but their effects on energy expenditure are complex [10]. Another study identified a novel mechanism linking chronic hyperglycemia to systemic metabolic impairment through reactive oxygen species (ROS)-driven mitochondrial and mtDNA release, which may contribute to metabolic injury in diabetes [9]. These findings provide context for understanding RMR in metabolic disease.

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The compounds and interventions described here are for laboratory research only. We do not provide dosing or medical guidance. Anyone considering a compound for themselves should speak to a licensed clinician.

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