How Does It Work?

Metabolism, quite simply, is the conversion of food to energy.

Metabolic rate is a measure of how much food, or fat, is converted to energy in a day. Resting metabolic rate (RMR) is the measurement of how much food, or energy, is required to maintain basic body functions such as heartbeat, breathing, and maintenance of body heat while you are in a state of rest. That energy is expressed in calories per day. So an RMR test shows how many calories you burn at rest, doing nothing more than sitting in a chair.

Indirect calorimetry (a measurement of metabolic rate) relies on the fact that burning 1 calorie (Kilocalorie) requires 208.06 milliliters of oxygen. Because of this very direct relationship between caloric burn and oxygen consumed, measurements of oxygen uptake (VO2) and caloric burn rate are virtually interchangeable.

Oxygen uptake requires a precise measurement of the volume of expired air and of the concentrations of oxygen in the inspired and expired air. The process requires that all of the air a person breathes out be collected and analyzed while they rest quietly. The KORR® indirect calorimeters contain a precision air flow sensor that measures the volume of expired air, and an oxygen sensor that measures the concentration of oxygen. Once the factors of humidity, temperature and relative humidity are accounted for, the KORR® instrument provides the most accurate results available in a compact metabolic analyzer.

Pre-test Requirements

It is desirable to measure a person’s metabolic rate at a true resting level. To ensure one is at rest, we recommend the following preparation:

  1. Avoid eating a meal 4 hours before the test.
  2. Avoid exercising on the day of testing.
  3. If possible, avoid the use of stimulants such as caffeine prior to testing.
  4. During the test it will be important to get into a comfortable position and relax as much as possible.
  5. Keep lips sealed lightly around the mouthpiece. It is important that all the air breathed out is analyzed by your KORR® machine.
woman on chair doing a breathing test
woman sitting in chair plugging nose with nose clamps

Conduct a Test

  1. Turn on your KORR® machine and wait while it automatically calibrates. The machine will indicate when calibration is complete. It is important that no hose or filter be attached during calibration.
  2. Expand the MetaBreather® hose to its full length (5 feet) and connect it to the machine. Be sure to use only a KORR® manufactured MetaBreather®, as use of any other breathing device will not insure accuracy and will void your KORR® factory warranty.
  3. Have the patient place the nose clip on his nose and the mouthpiece in his mouth, using his lips to seal around the edges. The patient should be relaxed and breathe normally.
  4. After approximately 10 minutes, the machine will end the test and prompt the tester to enter in patient data to compare patient results to averages. The results can then be printed out.

View PDF Example Print Out

Why Test RMR

Frequently Asked Questions

  • What is the effect of dieting on RMR?

    Each individual will react differently to dietary changes which is why a true measurement of RMR is so valuable. But if a patient reduces calories, don’t be surprised if their RMR also goes down. This may or may not be in conjunction with weight loss. It is critical to measure those changes periodically to make the necessary adjustments in diet and exercise to keep patients on track and avoid the dreaded “plateau.” (Martin)

  • What is the effect of aerobic exercise on RMR?

    Although many studies have been done regarding this question, there is not a simple answer to this question due to the many variables involved: the type, duration, frequency and intensity of exercise, degree of energy deficit, total daily calorie intake, and distribution of calories between fats, proteins, and carbohydrates. A conservative summary of the existing research would be that RMR does decrease significantly in response to a diet of less than 1000 Kcals per day, and that the addition of moderate intensity aerobic exercise (50%-70% maximum aerobic capacity) performed for 30-60 minutes, 4-5 times per week decreases this response but does not return RMR to baseline. (Connolly)

  • What is the effect of resistance training on RMR?

    When calorie intake remains unchanged, even a minimal resistance training program (10-15 mins per session, 3 times per week) can result in an increase in RMR. (Kirk)

    If calorie intake is decreased, most studies indicate that strength training can reduce the loss of fat-free mass (lean muscle) but not prevent the decline in RMR that invariably comes with dieting.(Geliebter)

    But studies are difficult to compare and summarize due to the many differences in the resistance training protocols and experimental designs. Researchers at West Virginia University found success maintaining RMR through intensive high volume resistance training designed to affect more muscle groups and by increasing protein intake to 80 g/day. (Bryner)

  • Why measure RMR rather than use predictive formulas?

    Predictive formulas have been used for years because an actual measurement through Indirect Calorimetry has not been practical. But the truth is, while predictions might hold their ground statistically, when applied to individuals, they are woefully inadequate. In an examination of published articles examining the validity of various predictive equations, Frankenfield, Roth-Yousey and Compher found that even the best equation (Miffin-St Jeor) was only within 10% of measured results. While 10% may seem statistically acceptable, for the individual desiring to lose weight, an RMR estimate that is 10% higher (2200 kCals) than an actual measurement of 2000 kCals a day would be significant. That additional caloric intake would result in 21 pounds gained in one year! Additionally, these same researchers noted that errors and limitations with equations exist when applied to individuals, and that “RMR estimation errors would be eliminated by valid measurement of RMR with indirect calorimetry.” (Frankenfield D, et al, J Am Diet Assoc. 2005 May;105(5):775-89.)

    Additional researchers at the University of Pennsylvania noted that the obese have Resting Energy Expenditures that are particularly difficult to predict. Their findings read, “Caloric prescription for weight reduction must be tailored to individuals rather than recommending the same caloric intake to persons with varying metabolic rates.” (Foster GD, et al, Metabolism. 1988 May;37(5):467-72.)


  • Does RMR change after weight loss?

    Often after a significant weight loss, RMR is depressed even lower than expected relative to the change in body composition. Most researchers point to this as a key factor in the high rate of weight regain among the formerly obese. Identifying this post-diet RMR is a vital step that is key to long term weight loss success. It gives the information necessary to set an appropriate caloric goal for maintenance and teach a patient to eat within the constraints of their new metabolic requirements. (JequierElliot)

  • Does RMR decline with age? Why?

    Resting Metabolic Rate declines slightly as individuals’ age. The cause is not clear. One reason may be due in part to a slowed metabolic rate of individual organs, such as the brain, liver, heart, and kidneys. These organs alone account for 60% of RMR in adults, and all but the heart decrease in mass with advancing age. Another cause may be a tendency for decline in physical activity and a sedentary lifestyle that leads to a decrease in lean mass and bone mineral density. (St-Onge)

  • Is RMR measurement recommended for TPN patients?

    Patients on TPN (total parenteral nutrition) may have a wide variety of diagnoses and nutritional status. This accentuates the challenge of determining the correct caloric prescription. Additionally, the stakes are high: excessive carbohydrate loads can stress the respiratory system and the liver, while inadequate intake can leave the patient at a nutritional deficit to recover from surgery, heal burns, or fight sepsis. Formulas have shown to be inadequate primarily because each has been developed from a particular population: healthy, or disease specific. No one formula has successfully predicted the metabolic needs of hospitalized patients on TPN. The formulas have been shown to both over- and underestimate REE.

    Economics are an additional concern related to TPN. Its significant cost must be considered when contemplating the value of determining a patient’s precise caloric need through RMR testing. A study by Foster measured REE in 100 TPN patients and compared those results to the published guidelines for determining TPN needs. Following those published guidelines instead of the actual REE resulted in the administration of 6947 excess liters of TPN per year! (FosterFlancbaum)

  • Is RMR affected by pregnancy?

    Studies show a considerable variation in the individual metabolic response to pregnancy, and thus the additional energy required to support a pregnancy. The individual increases in RMR can range from 456 KJ/d to 3389 KJ/d. Though clinicians often recommend an additional energy intake of 1250 KJ/d to their pregnant patients, the data suggests that this single recommendation is not justified. Metabolic testing would more precisely indicate the caloric needs of individual pregnant patients. (Kopp-Hoolihan LE)

  • What is the application for pediatric patients?

    In a study performed at the Children’s Hospital of Philadelphia, the pediatric population of both obesity and failure to thrive ages 2 months to 20 years were evaluated using both Resting Energy Expenditure and predictive equations. The predictive equations were Harris Benedict, the Food & Agriculture/World Health Org/United Nations Univ., and 2 from Schofield. The results showed such a wide variability in REE measurements with poor correlation to predictive equations that the researchers concluded that REE should be measured in patients for whom knowledge of caloric expenditure is required for clinical care. (Kaplan AS)

  • How is RMR affected by eating disorders?

    Studies indicate that these types of disorders can cause adaptive changes in metabolic rate, but these changes are highly individual and unpredictable. The question becomes relevant during nutritional therapy when it is time to set a caloric prescription. Caloric requirements based on empirical data or predicative formulas have been shown to be highly inaccurate for this population. For example, normal weight bulimics show evidence of a higher than predicted REE when binge eating, with a decrease in REE once eating behavior is controlled. For those suffering from anorexia nervosa, refeeding is associated with an increase in REE that cannot be explained by increased body mass. In each of these cases, consistent measuring of RMR throughout the treatment process is warranted to maintain the correct caloric prescription to aid recovery. (SchebendachKrahnLeonard)

  • Is there a familial link to RMR?

    Both the New England Journal of Medicine and the American Journal of Clinical Nutrition have published studies that examine the familial influence on variances in Resting Energy Expenditure. Both conclude that REE is moderately heritable, and a low rate of energy expenditure may contribute to the aggregation of obesity in families. (Ravussin EBosy-Westphal A)

  • How does caffeine affect RMR?

    As with any chemical ingested, rate of absorption, individual tolerance, and dosage relative to body weight all factor in to a person’s unique response. Under controlled conditions, studies suggest that caffeine can raise RMR at a rate relative to the dose ingested: around a 4% increase with 100 mg of caffeine, increasing up to as much as 15% with 500 mg (equivalent to 5 cups of coffee). It is a short lived increase – no more than 3 hours. This potential effect is why caffeine consumption is discouraged prior to testing with KORR products. (Dulloo,Acheson)

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