Metabolism

 

Many people misunderstand metabolism and how it is measured.  Metabolism is the energy used for all of the activities that take place inside of our cells. Our bodies continually make enzymes, proteins, and hormones.  Each cell reprduces to replace dead cells.  All of this takes energy to run the "machine" that accomplishes all of these tasks.  Metabolism does not involve movement or activity or exercise.  It happens at rest and is the sum total of every cell's calorie consumption to just be alive.  It is often referred to as the resting energy expenditure (REE) or the basal metabolic rate (BMR).

Metabolism varies among individuals based on gender, age, body composition and health status.  It is usually higher in men compared to women.  It slows as we age.  It is higher in people with increased muscle mass and less fat.  And some health problems such as low thyroid may slow the metabolism.  

We can calculate metabolism with a variety of tools.  The data inputs such as body build (height and weight), gender and age can be used to calculate an estimated metabolism.  Using a more detailed body composition such as a bio impedance scale report can yield a more accurate number.  But to truly measure metabolism requires some sophisticated testing.  

Calorimetry is the measurement of metabolism.  On each breath we take a measurable amount of oxygen is inhaled.  This oxygen is absorbed and makes its way thru the circulation into each cell.  There in the mitochondria of the cytoplasm the oxygen is consumed in a chemical equation that can be quantified - the Krebs's cycle.  This equation uses carbohydrate and other nutrients plus the oxygen to produce energy to drive metabolism.  A by-product of this equation is CO2.  Our machine is not 100% efficient, not every molecule of oxygen is consumed in the equation.  So when we exhale, we release CO2 and the left over oxygen.  Calorimetry measures the oxygen going in and the CO2 and oxygen being exhaled.  From this we can use the equation of the Krebs's cycle to accurately calculate the calories of the nutrients being consumed also.  The more oxygen is being consumed the more we are burning calories and the greater the metabolism. 

This oxygen consumption can be measured at rest or during activity.  When measured at rest, this gives the most accurate BMR or REE possible.  You may have seen elite athletes on a stationary bike, with a breathing mask on that is connected to a computer and other equipment.  The mask or mouthpiece is capturing in a closed circuit the amount of oxygen breathed in and out on every breath.  Now we can measure the amount of oxygen consumed over 10-20 minutes and calculate a very accurate metabolism.  This is very important to the athlete to test endurance, fitness and exercise capacity by measuring the total oxygen consumed. (VO2max).  At rest it gives us the BMR or REE.  It is very helpful to know the exact BMR / REE when recommending a diet or exercise program.  If the estimates for metabolism are off by even 150 calories then a patient may gain up to a pound every 3 weeks.  This adds up to over 17 pounds gained per year! 

To achieve success at weight loss and to keep the weight off you have to know a reliable measurement of metabolic rate.  We cannot rely on the estimates based on gender, height, weight and age.  Being off only a few calories per day leads to massive weight gain.  If you are interested in learning more about your individual metabolism, please contact our office.