Apr 01, 2015 1:00 PM

Author: Jen Brass Jenkins, MPC


We spend A LOT of time talking about calories, but how many of us know what they really are? Think about it. Have you ever tried to tell someone what a calorie is?

Cal-o-rie (noun): A unit of heat energy, 4.18400 joules, used to measure the energy value of foods
Small calorie (cal): 1cal is the energy needed to raise the temperature of 1 gram of water through one degree Celsius.
Large calorie (Cal): 1Cal is the energy needed to raise 1 kilogram of water by one degree Celsius.*

The Human Body & Calories

Our bodies need to burn fuel (food, glorious food) to create energy. Since a calorie is a measurement of energy, it tells us how much energy it took our body to burn the fuel we absorbed (chips, fruit, burger, fries, and everything else we ate). If we eat more fuel than we use, that fuel can be stored as fat (elementary my dear Watson). Hence, our obsession with counting calories as we try to measure how much fat we will gain from the food we eat.

The Calorie Count on Your Treadmill Is Lying to You!

It’s not intentional, but when you work out at the gym, the calorie count that your workout equipment (or device or app) reports is not necessarily accurate. To get a true idea of the calories you burn in a single day, we took one of our own, Cole, into the performance lab at our Pulmonary Services clinic.

The Calorimetry Machine: Measuring Resting Metabolic Rate

Calorimetry tech putting Cole in the measurement bubble

The bubble you see Cole sitting inside measures indirect calorimetry or resting metabolic rate (also called the basal metabolic rate). This is the number of calories you burn regularly just going about your daily life. While we watched Cole breath in and out, the technician, Kathryn Krause, told us about how the machine works.

The bubble around Cole’s head allows Krause to track the amount of carbon dioxide (CO2) that he was exhaling. You probably remember from high school biology that CO2 is a waste product of energy after the body burns food. Once Cole exhaled the same amount of CO2 (at a steady rate) for five minutes, Krause told us we had an accurate measurement to calculate the calories he burned in a day.

The Weir Equation

The calorimetry machine measuring Cole's CO2 output
"The calorimetry machine measuring Cole's CO2 output"

The formula used to calculate basic metabolic rate is called the Weir formula:

REE (kcal/day)= [VO2 (3.941)+VCO2 (1.11)] 1.44

  • VO2 = Oxygen burned
  • VCO2= Carbon dioxide burned

Fortunately, we didn’t have to do the math. The calorimetry machine gave Krause a number: 

In one day Cole burns approximately 1,999 calories. 

Now that he knows what his resting metabolic rate is, Cole can go on to calculate how many calories he really does burn while exercising. That, however, is just a little too much math for the day.

Fortunately for you, this post is just the first in a series we will be doing about measuring fitness and performance. Check back to learn more about applying the science of fitness to your body!

Get Your Own Basal Metabolic Rate Measured

If you want to measure your own basal metabolic rate, schedule an appointment for our performance technicians either through the pulmonary performance lab or PEAK Health & Fitness testing services.

*Thank you Google


Jen Brass Jenkins, MPC

Jen is the web content manager on the Interactive Marketing and Web team. She manages projects and works with clinical services, departments, and colleges across University of Utah Health Sciences. She also writes and edits many, many things. Find her on Twitter @chrlichaz.

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