Calorie targets drive almost every weight management plan, yet most start from an estimate. A predictive equation takes age, sex, height, and weight and returns a number. Whether that number fits the patient in the chair is a separate question. 

Resting metabolic rate (RMR) testing answers it with a measurement. This guide covers how measured RMR works in practice, how it differs from estimation, and how different specialties use it to set calorie targets and keep patients engaged. 

What Is RMR Testing? 

Resting metabolic rate is the energy the body uses at rest. It accounts for most of a person’s daily calorie needs. Total daily energy expenditure is RMR plus the energy spent on daily activity. 

Indirect calorimetry measures RMR by capturing a patient’s oxygen consumption (VO2) and converting it to a calorie value. Metabolic carts and handheld indirect calorimeters use this method. The result gives the clinician a patient-specific baseline for building a calorie budget. 

Measured RMR vs. Predictive Equations: Why It Matters 

Equations like Harris-Benedict and Mifflin-St Jeor are fast and free. They also rest on population averages, so they cannot see individual differences. Body composition, medications, genetics, illness, and obesity can all pull a patient’s true metabolic rate away from the estimate. 

A frequently cited study, Foster et al. (1988), found that people with similar height, weight, age, and sex can still differ widely in measured RMR. Microlife’s materials illustrate this with two women who both weigh 158 lbs. One measured about 1,571 kcal/day and the other about 1,252 kcal/day. Same scale weight, roughly 300 kcal/day apart, and a plan built from an equation would treat them identically. 

The Academy of Nutrition and Dietetics (formerly the American Dietetic Association) recommends indirect calorimetry for the most accurate assessment of nutritional needs when it is available.  

How Measured RMR Sets the Calorie Target 

The workflow is simple: 

1. Measure. The patient breathes into the device for a short, standardized test. 

1. Build the budget. Add lifestyle, occupation, and exercise habits to the RMR to estimate total daily energy needs. 

1. Apply the goal. Set a calorie target based on the patient’s weight goal and timeline. 

1. Review and adjust. Revisit the plan as weight, activity, or clinical status changes. 

With MedGem, the Analyzer software (included with the device) turns the RMR into a personalized calorie budget. It accounts for lifestyle, exercise, and weight goals, and it produces a plan the patient can take home. 

RMR Testing Use Cases by Specialty 

Registered Dietitians and Nutrition Practices 

For RDs, measured RMR replaces the largest assumption in the nutrition assessment. It is useful when: 

• A patient’s estimated needs don’t match their real-world response to a plan 

• Patients have obesity, where predictive equations can be less reliable 

• A patient is regaining weight after a diet and you need to rule out an overestimated calorie target 

• You want a documented baseline for a medical nutrition therapy plan 

Endocrinologists 

Metabolic questions are a core part of endocrine practice. Medications, hormonal conditions, and illness can all influence energy expenditure. Though measured RMR doesn’t diagnose the issue, it gives you an objective data point to discuss alongside the clinical picture, rather than relying on an estimate that can’t account for those factors.  

Cardiologists 

Weight management is often part of managing cardiovascular risk. For cardiology practices that counsel patients on weight, a measured RMR supports a calorie target built for the individual rather than a generic diet prescription. It also gives the conversation a concrete number to anchor to.  

Bariatricians and Bariatric Surgery Programs 

Bariatric programs depend on precise, individualized nutrition guidance before and after treatment, and patients in these programs often have higher body weights, where estimation error matters most. Measured RMR helps teams: 

• Set realistic calorie targets for weight loss programs 

• Establish a baseline before an intervention 

• Reassess when progress stalls 

Sports Medicine and Performance Practices 

Sports medicine and performance clinics use RMR to match fuel to training load, whether the goal is fat loss, weight maintenance, or avoiding under-fueling. Measured RMR provides the baseline, and training demands are layered on top.  

Wellness and Weight Management Clinics 

For wellness clinics and medically supervised programs, RMR testing is a differentiator: a short, objective measurement that gives clients a personalized starting point. It also works as a visible service in your program that patients can see and understand. 

Using RMR to Show Patients Their Progress 

Calorie targets work better when patients understand where the number came from. A measured RMR is easy to explain, because it is their own number. That helps with: 

• Buy-in. Patients are more likely to trust a plan built from their own measurement than from an online calculator. 

• Expectation setting. A specific daily budget makes it easier to talk about realistic rates of change. 

• Retesting and follow-up. Repeat measurements give you a reason to bring patients back and a way to review how the plan is working. 

• Take-home documentation. The MedGem Analyzer software generates reports that can be printed or saved as a PDF and emailed, so patients leave with a written plan. 

What to Look for in an RMR Testing Device 

When evaluating indirect calorimeters for a clinical setting, consider: 

• Regulatory status. Is the device FDA 510(k) cleared for the intended use? 

• Validation evidence. Has it been compared to reference methods such as the Douglas bag or metabolic carts? 

• Workflow. Is it portable, quick, and easy for your staff to administer? 

• Software. Does it help you convert RMR into a usable plan? 

• Support. Will the manufacturer help your team with training and questions after the sale? 

MedGem and BodyGem Indirect Calorimeter for Clinical Settings 

The Microlife MedGem is a handheld indirect calorimeter. It is an FDA 510(k)-cleared Class II medical device for measuring resting metabolic rate. Here’s how it fits the criteria above: 

• Simple to administer. The patient breathes into the device, and the RMR appears on the LCD screen. 

• Portable and quick. Results take 10 minutes or less, and the device is self-calibrating. 

• Validated. BodyGem and MedGem have been validated against the Douglas bag method and commonly used metabolic carts. Published research, including Nieman et al. in the Journal of the American Dietetic Association (2003), is listed on Microlife’s clinical validations page. 

• Backed by software. The Analyzer software turns each measurement into a personalized plan and patient report. 

• Hygienic. Single-use mouthpieces and nose clips make the device suitable for use across multiple patients. 

• Potentially reimbursable. Medicare and some insurance companies may reimburse metabolic assessments using the suggested AMA CPT code 94690.  

Frequently Asked Questions 

How long does an RMR test take?
A MedGem measurement takes 10 minutes or less. 

What is the difference between indirect calorimetry and a predictive equation?
Predictive equations estimate RMR from population averages. Indirect calorimetry measures the patient’s oxygen consumption directly. 

Which specialties use RMR testing?
Dietitians, endocrinologists, cardiologists, bariatricians, and research scientists are among the professionals Microlife lists as MedGem users. 

Is there a CPT code for RMR testing?
Microlife suggests CPT 94690 for MedGem measurements. Providers should verify coding and payer requirements for their practice. 

Do patients need to prepare for the test?
Yes. Pre-test instructions affect measurement quality, so follow the manufacturer’s guidelines. You can view guidelines for the BodyGem here.  

Bring Measured RMR Into Your Practice, With Support Behind It 

Adding RMR testing is a workflow decision as much as an equipment decision, and the support behind the device matters. Microlife backs MedGem and BodyGem with full access to its expert staff and toll-free customer support at 1-866-950-1404, along with a Quick Start Guide that includes training and a user manual on USB, plus marketing materials to help you promote the service.
Talk to Microlife’s team: 1-866-950-1404 →