Article # 362. Indirect calorimeter

Calorimetry is the act of measuring the heat of chemical reactions or physical changes, or the science of making such measurements. Calorimetry is performed with a calorimeter. The word calorimetry is derived from the Latin word calor, meaning heat and the Greek word μέτρον (metron), meaning measure. Scottish physician and scientist Joseph Black, who was the first to recognize the distinction between heat and temperature, is said to be the founder of the science of calorimetry.

What exactly is an indirect calorimeter?

It is a device that accurately and quickly measures your resting metabolic rate (RMR) and oxygen consumption, or VO2. In just a few minutes, the machine calculates your metabolism to determine your body's internal efficiency and helps your healthcare provider understand your caloric needs for effective medical nutritional therapy and weight management.  Inadequate nutrition can prevent you from reaching your health goals. In addition to weight management, this test provides the information you need to achieve greater personal control of weight-related conditions such as diabetes, chronic obstructive pulmonary disease (COPD), burns, liver disease and sleep apnea.

How Do I Need to Prepare for the Test?

To obtain a true resting metabolic rate, it is important that your body is in a calm and relaxed state. If you have been active, stressed, or if you have recently eaten or exercised, the measured RMR will be accurate for that condition but not representative of your actual RMR.

Ideally, RMR is measured 8-12 hours after eating or exercise. If this is not possible, the following conditions should be met in addition to sitting quietly and relaxing for 15 minutes prior to the test:

·        Avoid eating or drinking beverages that contain calories or caffeine for 2-4 hours prior to the test.

·        Avoid exercising (cardiovascular and strength training) for 4 hours prior to the test.

·        Avoid nicotine consumption for at least 1-2 hours prior to the test.

·        Avoid taking nutritional supplements and medication that contain ephedra, Ma Huang, or pseudoephedrine for at least two hours prior to the test.

Metabolism is different among individuals and is influenced by many factors; therefore you should measure your metabolism regularly during a weight management program.

Metabolism can vary from day to day and within the same day. That's why it's important to measure RMR under similar conditions at the same time of the day, in the same position, and fully relaxed. If normal conditions for you include taking nutritional supplements, caffeine, nicotine, or medications, then it is important to acknowledge this as part of your daily routine.