It is all about the numbers

Happy February! We are officially one month into the year and where are you with your weight wellness goals?  Maybe you have a lot to lose, or a little to gain, either way, when you just consider the scale, weight wellness is all about the numbers.

In order to lose weight, one must consume less calories daily than the body is expending in energy.  Generally a deficit of around 500 calories a day (or 3,500 calories a week) will produce the loss of 1lb.  This deficit can come from calorie restriction (eating less), energy expenditure (exercise) or a combination of the two.

Sounds easy right?  Let’s see…how much energy, as expressed in calories, are you expending in a day? If you need to eat less than this, you must have an idea of what this number is.  We do not want to go below our Basal Metabolic Rate (BMR), or what our body burns in normal body functions like breathing,  as that will stall out our metabolism and put us into starvation mode.  In other words, eating too little will cause the body to hang onto fat instead of burn it.

I’m going to throw some numbers at you that will allow you to calculate not only your BMR but also your Total Daily Energy Expenditure (TDEE) which takes into consideration your lifestyle/exercise/activity.  Creating a deficit below your TDEE but over your BMR will help promote fat loss while preserving muscle mass and without stalling out your metabolism.

In order to more accurately calculate BMR and then TDEE it is important to have an accurate measurement of your body fat percentage.  Hand held body fat monitors or caliper testing are generally very accurate.  If you do not have access to either of these or prefer not to handle the calculations, here are some links to online calculators that do the work for you without your body fat percentage.

Online BMR calculator

Online TDEE calculator

For those of you with access to your body fat percentage and with a love of math, we will be using the Katch McArdle formula.

First, we must calculate BMR here is the equation:

BMR = 370 + (21.6 * LBM)

LBM refers to Lean Body Mass expressed in kilograms for this equation.  You calculate your LBM by subtracting your body fat weight from your total body weight, giving you the weight of everything in your body except the fat.  Here is the equation

LBM = (1-Body Fat % expressed as a decimal) * total body weight (in kgs or lbs)

So if I am 25% body fat and weigh 160lbs, here is what that would look like:

LBM = (1-.25) * 160       Lean Body Mass = 120 lbs

I can than divide this LBM number by 2.2 to get my LBM in kgs

120/2.2 = 54.54 kg of LBM

I can now use my LBM in kgs to calculate my BMR:

370 + (21.6*54.54) = 1,548 calories a day

Without exercise or any daily activities (beyond basic functions like breathing, digestion, etc) my body is burning 1,548 calories a day.  I do not want to eat below this number for a prolonged period of time as I will stall out my metabolism, causing my body to go into starvation mode and hold onto fat.

Now that we know BMR, we can calculate TDEE which accounts for exercise and lifestyle.  We are going to multiply our BMR by the following numbers depending on your activity level:

  • by 1.2 if you exercise 1 to 3 hours per week
  • by 1.35 if you exercise 4 to 6 hours per week
  • by 1.5 if you exercise vigorously for 6 or more hours per week.

The resulting number will be a fairly accurate measurement of the total energy you are burning each day.  You can choose to create a deficit in calories below your TDEE (but not below your BMR) through eating less or exercising more.

In the example above, my BMR is 1,548 calories a day.  If I exercise 1 to 3 hours per week my TDEE is (1548 * 1.2) = 1857 calories.  If I eat 1857 calories I will maintain my weight.  If I eat below it I will lose weight.  I could eat around 1600 calories to create a 257 calorie deficit (about .5lb a week of loss).  I could also increase exercise to 4 to 6 hours per week raising my TDEE to (1548 *1.35) = 2,089 calories.  Now if I eat around 1600 calories, I have a deficit of 489 calories a week, getting me closer to 1lb loss/week.

Changing the number on the scale is truly as simple as calories in vs energy out.   By calculating BMR and TDEE and basing your calorie deficit on those numbers, you are in a better position to maintain muscle mass while losing fat and to turn your metabolism into a fat burning machine.

This article was submitted by Jodi Langellotti, an avid runner, fitness enthusiast and health and wellness coach.


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