For patients
Metabolic rate and energy
Most calorie targets are produced by an equation that guesses your metabolic rate from your age, sex, height and weight. It is possible to measure it instead.
The difference between calculated and measured
A predictive equation takes population averages and applies them to you. That works reasonably for the average person and badly for anyone who is not — which includes people with a lot of muscle, people who have lost a lot of weight, people with thyroid disease, and older adults with reduced lean mass.
Indirect calorimetry measures it directly. You breathe normally for around ten minutes while oxygen consumption and carbon dioxide production are recorded, and from those two figures the device calculates resting energy expenditure and the respiratory quotient.
What the two outputs mean
Resting energy expenditure
The energy your body uses at rest, which is the large majority of what most people use in a day. This is the number a calorie target should be built on, and it is the number most often wrong when someone says a diet stopped working.
Respiratory quotient
The ratio of carbon dioxide produced to oxygen consumed. Because burning fat and burning carbohydrate consume oxygen and release carbon dioxide in different proportions, this ratio indicates which fuel your body is predominantly using at rest. A lower value indicates fat is the predominant fuel; a higher value indicates carbohydrate.
Neither number is good or bad on its own. Both are useful because they can be repeated, and because they explain results that otherwise look like a failure of willpower.
Why this belongs with the rest of the assessment
Resting energy expenditure is produced overwhelmingly by lean tissue, so the measurement is only interpretable alongside body composition. And fuel use at rest sits directly downstream of insulin resistance, which is measured in the same visit.
Preparation matters here more than anywhere
The measurement is taken at rest after an overnight fast, with no caffeine and no nicotine. Food, coffee, a cigarette or a brisk walk from the parking lot will all change the result. Full preparation instructions.
If you are a clinician: the same subject written for the person ordering the test is at the full test description.
Talk to someone about testing
Tell us what you are trying to find out and we will explain which Measura assessments answer that question, what each one involves, and how the results are reviewed with a clinician.
4477 Woodson Rd, Suite 201, St. Louis, MO 63134. Monday to Friday, 9:00 a.m. to 5:00 p.m. Please do not send symptoms, diagnoses or images through a web form — a website form is not a secure medical channel. Call us with clinical detail.
Common questions
Is my metabolism really slow?
It is a testable claim rather than a belief, and the answer is often not what people expect. Measured versus estimated metabolic rate.
Why did my weight loss stall?
Resting energy expenditure falls as lean mass falls, so a target set at the start of a program may no longer be right. Measuring resolves it. Read more.
How long does the measurement take?
About ten minutes of quiet breathing. What the appointment feels like.
Do I need to fast?
Yes, overnight, with water allowed. Preparation instructions.
Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP, medical director of Measura. Last reviewed .