Tuesday, July 7, 2015

Back to Basics: Calories, Metabolism and Energy, What Do They all Mean? Part I

Author: Dr. Andrew Jagim PhD CISSN, CSCS

Terms like metabolism, calories and energy get thrown around a lot in fitness articles and catch phrases such as "boost your metabolism" or "burn calories by doing this...." but what do they all mean? As you might expect these terms are very closely related and often times even used interchangeably however there are some differences among them.  In this "Back to Basics" series we are going to take a step back and define some of the terms commonly used in the fitness world when in fact they may not be completely understood.

Let's first take a look at the term calorie.  The definition of a calorie from a physics perspective is the amount of energy or heat needed to raise the temperature of 1 gram of water 1 degree Celsius and we use devices known as Bomb calorimeters  to directly measure the amount of calories in foods by burning food items and identifying the temperature change or what it takes to raise the water by 1 degree Celsius. WTF?! A little different than how many M&M's you burned on your run isn't it? Luckily there is an easier way to measure heat production aka energy expenditure by monitoring the gases we expire which a lot of prediction equations are then developed from.  These equations are what gps monitors, treadmills and elipitcals use to estimate how many calories you are burning. But again, what are calories from a non-physics perspective?

Well, all of the process that occur within our body are used to produce or use energy and are what we rely on to breathe, digest our food, transport blood & nutrients, move etc.  All of these reactions that are constantly on-going require energy to occur.  The energy currency within our bodies that we use is referred to as adenosine triphospate or ATP.  So, why don't devices like FitBit tell you how many molecules of ATP you burned during your run? First off because the number would probably be in the millions. Second of all, we use a more robust term such as calorie to describe how much work is required to cause a certain change (i.e. move).

So how do we get from heating water and measuring gases to burning calories and losing weight?  Food has energy or calories in it in the form of chemical bonds.  The cells within our bodies then use this energy in combination with various metabolic-pathways to create a bio-available or usable form of energy within the body known as ATP.  We are not machines, we don't use calories, we use energy and measure it by using the unit: calories. Life's costs are ultimately made available or paid for by the conversion and transfer of energy within food that is made available to use through the process of digestion. This transfer of energy from the chemical bonds of food to cells within our body is quantified in terms of calories as again, they are  just a unit of energy measurement. Ultimately it's this number, or calories consumed/expended, that we use to monitor our body's state of energy balance which could be calculated as energy in (calories eaten) versus energy out (daily calorie expenditure).

So next time you look at a food label and it says you are consuming 270 calories, you are essentially eating a food item that has the potential to release 270 calories worth of energy when the chemical bonds within the food are broken down during digestion.  However, remember that a calorie does not always elicit the same response within the body (for more on a "A calorie is not just a calorie" check out our previous post here).  Conversely if you were trying to burn 270 calories, you would need to complete enough work/movement that would require 270 calories worth of energy to complete the task beyond that of your normal daily calorie expenditure.

Stay tuned for the next post in this series when we discuss the term metabolism and metabolic rates and what all goes into this magic number.

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