Mixed messages and information about metabolic rate and the calories and workouts it takes to burn fat make losing weight a daunting task.  In this post I briefly show the difference between weight loss and fat loss and then hope to get you started determining your own caloric needs by defining BMR and calculate your daily energy expenditure.  These pieces of data will help you find a good starting point for weight loss or body composition goals.

 

Body Weight vs Body Fat %

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The photo on the right is the cross section of three different thighs, all the same size.  The thigh in the middle is made up mostly of adipose tissue (fat) while the photos on top and bottom are made up mostly lean mass.  All these cross sections are of legs that look the same size and while the photos on top and bottom have more lean mass, they will weigh more on the scale.  The man with the very high percent body fat in the middle will weigh less on the scale.   Even though the scale indicates they are “smaller”, the individuals on top and bottom is the same size, is stronger, and has legs that are functionally sound.

 

The Basics of Losing Weight

When I work with clients who want to lose weight or lose body fat, I always start with BMR.  BMR stands for basal metabolic rate and is the amount of energy you need to maintain basic body function while resting.  An accurate measure of BMR is conducted under very restrictive conditions.  The subject must be completely rested (sympathetic nervous system is inactive) but awake, in a temperate environment, with the digestive system completely inactive. It is under these conditions that your energy will be used only to maintain your vital organs, which include the heart, lungs, kidneys, the nervous system, intestines, liver, lungs, sex organs, muscles, and skin.

Basal metabolism is usually the largest component of a person’s total caloric needs. The daily calorie needs is the BMR value multiplied by a factor with a value between 1.2 and 1.9, depending on the activity level.

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*BMR derived from the Mifflin St. Jeor Equation


BMR only represent resting energy expenditure, to calculate your total daily energy expenditure (TDEE), multiply your BMR by the appropriate activity level using the Harris-Benedict formula, as follows:

Activity Level Activity Factor
Sedentary
Light or no exercise and desk job
BMR x 1.2
Lightly Active
Light exercise or sports 1-3 days a week
BMR x 1.375
Moderately Active
Moderate exercise or sports 3-5 days a week
BMR x 1.55
Very Active
Hard exercise or sports 6-7 days a week
BMR x 1.725
Extremely Active
Hard daily exercise or sports and physical job plus training 2 x week
BMR x 1.9

This number shows approximately how many calories you should consume to maintain weight. If your goal is to lose weight, remember that basal metabolic rate varies between individuals. Studies have shown differences in BMR when comparing subjects with the same lean mass to be a whopping 28-32% higher than others.  What this means is that calculating your BMR is a starting point for weight loss but some variables are not accounted for in the equation.  

Estimating daily calorie requirements is challenging. While even the best calculators cannot determine an accurate metabolic rate for every individual, calculators based on research can be a very helpful starting point.  These calculators and equations give you a science-based platform to start with.  From there you must use trial, error and careful self-monitoring to achieve your goals.