Short answer: Resting Metabolic Rate (RMR) is the amount of energy your body uses at rest to maintain essential functions such as breathing, circulation and body temperature. Because RMR makes up a significant proportion of your daily energy expenditure, understanding it can provide useful insight into your individual energy needs and help inform personalised nutrition, weight management and health strategies.
Long answer:
Even when you’re resting, your body is constantly using energy.
Your heart is beating, your lungs are working, your brain is active and your body is maintaining its temperature, repairing tissues and supporting many other essential processes.
The energy required to support these functions is known as your Resting Metabolic Rate (RMR).
RMR is usually expressed as the approximate number of calories, or kilojoules, your body uses over a 24-hour period while at rest.
What Affects Your Resting Metabolic Rate?
RMR varies considerably from person to person and can be influenced by several factors, including:
- Age
- Sex
- Body size
- Muscle mass and body composition
- Genetics
- Hormonal (i.e. thyroid levels) and health factors (i.e. stress)
- Changes in body weight
- Energy intake and periods of significant calorie restriction
- Stimulants
This is why two people of a similar weight may have different resting energy requirements.
In particular, lean body mass is an important contributor to RMR, because metabolically active tissues require energy even while the body is at rest.
Why Is RMR Important?
Understanding your RMR provides information about how much energy your body uses before physical activity and other components of daily energy expenditure are taken into account.
This information may be useful when developing an individualised approach to:
- Weight management
- Nutrition planning
- Sports and exercise nutrition
- Maintaining muscle during weight loss
- Supporting healthy ageing
- Understanding changes following significant weight loss
- Chronic Fatigue
However, RMR is only one part of the picture.
Your total daily energy expenditure also includes the energy used for physical activity, digestion and everyday movement. For this reason, an RMR result should not be interpreted as the exact number of calories you should eat each day.
How Is Resting Metabolic Rate Measured?
Resting Metabolic Rate can be estimated using population-based equations based on factors such as your age, sex, height and weight.
Alternatively, it can be measured using indirect calorimetry, which is a more accurate measure of your true resting metabolic rate.
Indirect calorimetry measures the oxygen your body consumes and the carbon dioxide it produces while you are resting. This information is then used to estimate how much energy your body is using at rest.
At WLC Medical, we use the ECAL Metabolic Testing System to measure Resting Metabolic Rate.
Why Measure RMR Instead of Relying on an Estimate?
Predictive equations can provide useful estimates of energy requirements, but they are based on population averages and cannot account for every individual’s metabolism or body composition.
Measuring RMR via indirect calorimetry provides information based on your body’s actual resting energy expenditure at the time of testing.
This may be particularly useful for people who want a more individualised understanding of their metabolism rather than relying solely on an estimated figure.
RMR results are best considered alongside factors such as your body composition, activity levels, health history, nutrition and individual goals.
Can Your RMR Change Over Time?
Yes.
Your Resting Metabolic Rate is not necessarily a fixed number throughout your life.
Changes in body weight, muscle mass, age, health and energy intake can all influence your resting energy expenditure.
For example, during significant weight loss, RMR commonly decreases partly because the body becomes smaller and requires less energy to maintain. Other physiological adaptations may also contribute to changes in energy expenditure.
This is one reason why energy requirements can change over time rather than remaining the same indefinitely.
How Do RMR and Body Composition Work Together?
Body weight alone cannot show how much of your body is made up of fat, muscle and other tissues.
A Total Body Composition DEXA Scan provides detailed information about your body composition, including lean mass, fat mass and visceral fat, while an RMR test via indirect calorimetry provides information about how much energy your body uses while at rest.
Looking at these measurements together can provide a broader understanding of your body composition and metabolism.
This may be particularly useful for people establishing a baseline, monitoring changes over time, working towards health or fitness goals, or navigating significant changes in body weight.
Key Takeaways
- Resting Metabolic Rate is the energy your body uses to maintain essential functions while at rest.
- RMR varies between individuals and is influenced by factors including body size, body composition, age and health.
- RMR can be estimated using predictive equations or measured using indirect calorimetry.
- Measuring RMR can provide more individualised information about resting energy expenditure.
- RMR is only one component of your total daily energy expenditure and should not be treated as your exact daily calorie requirement.
- Combining RMR information with body composition and other health information can provide a broader understanding of your individual needs.
How WLC Medical Can Help
At WLC Medical in Belmont, we use indirect calorimetry to understand an individual’s resting metabolic rate in all of our Dietitian appointments, providing our Accredited Practising Dietitians with additional information about your individual resting energy requirements to help inform personalised nutrition advice. Using indirect calorimetry, we can also assess an individual’s fuel utilisation, including the relative contribution of fat and carbohydrates to energy production, as well as their metabolic efficiency.
For people wanting a more comprehensive understanding of their body composition, metabolism or bone health, we also offer two assessment packages:
- DEXA Sports Package – combines a Total Body Composition DEXA Scan with ECAL Resting Metabolic Rate testing to provide information about your muscle mass, body fat, visceral fat and resting energy expenditure.
- Health Insights Package – combines a Bone Density DEXA Scan, Total Body Composition DEXA Scan and ECAL Resting Metabolic Rate testing, providing a broader assessment of bone density, body composition and metabolism.
Both packages are completed during a 60-minute appointment with an Accredited Practising Dietitian.
Related Articles
Continue learning about body composition, metabolism and DEXA:
- Why Body Weight Doesn’t Tell the Whole Story
- What Is Visceral Fat and Why Does It Matter?
- Bone Density Scan vs Body Composition Scan: Which DEXA Scan Is Right for You?
Want to Better Understand Your Metabolism?
If you’d like to learn more about Resting Metabolic Rate testing or which assessment may be suitable for you, our team at WLC Medical is here to help.
To book an appointment or speak with our friendly team, call (08) 6263 7778, or book online through our website.
References
- Academy of Nutrition and Dietetics. Guidance relating to indirect calorimetry and energy expenditure.
- American College of Sports Medicine (ACSM). Guidance relating to metabolism, body composition and energy expenditure.
- National Institutes of Health (NIH). Research relating to resting energy expenditure and body composition.
- International Society for Clinical Densitometry (ISCD). Official Positions.
- Peer-reviewed research relating to indirect calorimetry, resting energy expenditure and metabolic adaptation.
Last reviewed: November 2026
This article is intended for general educational purposes only and should not replace personalised medical or nutrition advice. If you have questions about your metabolism, nutrition, weight management or overall health, please speak with your GP, Accredited Practising Dietitian or another qualified healthcare professional.
