Preparing for a metabolism (RMR) and body composition measurement

The resting metabolic rate measurement is one of the most sensitive tests we run. A coffee, a morning workout or ten minutes of hurried walking before you walk into the lab are enough to push the result up and send you home with the wrong calorie number. That is why the instructions here are stricter than for our other tests — and why it is worth following them.

The rules, at a glance

• Fasting: at least 8 hours without food — in practice, come in the morning on an empty stomach. Water is allowed and encouraged.
• No caffeine: coffee, tea, cola, energy drinks, pre-workout supplements — none of these on the morning of the measurement.
• No exercise: neither moderate nor vigorous, from the previous evening onwards. The raised oxygen consumption after exercise lasts for hours.
• No nicotine on the morning of the measurement, and no alcohol in the previous 24 hours.
• Rest beforehand: you will lie down quietly for 15–20 minutes before the recording starts. Do not rush to make it on time — arrive with time to spare.
• Morning, at a consistent time: if you are going to repeat the measurement, keep to roughly the same time of day so that the two measurements can be compared.

These are not arbitrary lab rules. The systematic review by Compher and colleagues (2006), which is the reference standard for measuring RMR by indirect calorimetry, shows that food, alcohol, caffeine and nicotine alter measured metabolism for a variable number of hours after consumption, that moderate and vigorous physical activity has a prolonged residual effect, and that 10–20 minutes of rest before the start are enough to clear the effect of ordinary daily activities.

What will happen in the lab

You will lie down comfortably in a quiet, dimly lit and thermally neutral room. A mask or a canopy that collects your exhaled air will be placed over you, and the analyser will measure the oxygen you consume and the carbon dioxide you produce. You will be awake but still and relaxed — you do not have to do anything, not even control your breathing. The recording lasts a few minutes; we keep the section in which your breathing has stabilised.

The relationship between oxygen and carbon dioxide also gives us the respiratory quotient, that is, whether your body at that moment is burning mainly fat or mainly carbohydrate. This is the information that no equation and no “smart scale” can give you.

Body composition

If your appointment also includes a body composition measurement — they are usually done together — the following apply as well:

• Normal hydration. Neither dehydrated nor “loaded” with fluids; both shift the result.
• Empty your bladder before the measurement.
• No creams or oils on the skin on the day of the measurement.
• Light clothing that allows access to the skinfold measurement sites.
• In women, the phase of the cycle affects body fluids. It is not a reason to postpone — but it is a reason to keep to roughly the same phase for repeat measurements, so that the comparison is fair.

The order matters: metabolism first, body composition second. Skinfold measurement requires movement and standing, which would disturb the rest that RMR demands.

If you have broken one of the rules

Tell us before we start. If you have eaten or had a coffee, the measurement will show a higher metabolism than the real one — and because your nutrition plan will be built on that number, we would rather postpone it than give you a figure that will mislead you for months. Rescheduling is free of charge.

After the measurement

You will receive your measured resting metabolic rate in calories per 24 hours, its comparison with the predicted value, the respiratory quotient and your fuel-burning profile, together with your body composition. Everything is recorded in your account at results.ergometrictests.com, so that the next measurement sits next to this one and the change is visible.

Do you want to understand exactly what it measures and why it differs from the formulas? Read the article on resting metabolic rate. If your appointment concerns exercise tests or field measurements, see preparing for ergometric tests.

References

• Compher C, Frankenfield D, Keim N, Roth-Yousey L (2006). Best practice methods to apply to measurement of resting metabolic rate in adults: a systematic review. Journal of the American Dietetic Association 106(6):881–903. doi:10.1016/j.jada.2006.02.009

Source of the bibliographic reference: PubMed.