When trying to lose weight, one of the most important things to know is how many calories you are burning every day. Most diet programs will recommend a static number of calories, like 1200, 1500 or 1800, without taking into account your individual size, shape and lifestyle, when, in fact, there is a much more accurate and scientific method for calculating the number of calories you burn every day.
Resting Metabolic Rate
To begin, you will need to know your resting metabolic rate, or RMR This is the number of calories that your body burns when completely at rest, at least 12 hours after your last meal. To accurately measure RMR, you would need an expensive test with a machine that uses a process called "indirect calorimetry," which is not an option for most people. Fortunately, there are several research equations which can estimate RMR. One such set of equations, which has a high degree of predictability, was developed by Kelley Martin, RD, MPH, and team at the Medical University of South Carolina in 2004.
These are the inputs to their equations:
Race: white = 0, black = 1
Diabetes Status Index [DSI]: normal = 0, pre-diabetic = 1, frank diabetic = 2
Body Mass Index [BMI]: from a BMI calculator or table, or [weight in kg] / [height in meters]^2
Lean Body Mass [LBM]: weight in kg x [1 - body fat %]
And these are the equations:
Female: 803.8 + 0.3505 x Age x [BMI - 34.524] - 135 x Race + 15.866 x LBM + 50.90 x DSI
Male: 909.4 + 0.3505 x Age x [BMI - 34.524] - 135 x Race + 15.866 x LBM + 9.1 x DSI
An RMR Calculation Example
Here is an example of this calculation for Sam, a 42-year-old, 6'2" black male with normal, healthy blood sugar, who weighs 220 lbs. and has 9 percent body fat:
1) Sam's BMI from a table is 28.2
2) Sam's LBM = [220 lbs / 2.2 lbs/kg] x [1 - 9%] = 91 kg
3) Sam's RMR = 909.4 + 0.3505 x 42 x [28.2 - 34.524] - 135 x 1 + 15.866 x 91 + 9.1 x 0 = 2,125 calories per 24 hours, or 89 calories per hour
Again, this is Sam's resting metabolic rate--the number of calories he burns when he is sitting in a chair, doing nothing.
Activity Calories
Since Sam does not spend his entire day sitting still, and neither do you, the next step is to figure calories burned in daily activity. The modern means of calculating activity calorie burn is to use a concept called MET, or metabolic equivalent task. METs are numbers like 1.5, 6.3 or 12, which tell us how many calories an activity uses, relative to rest. Here are some example METs from "The Compendium of Physical Activities," compiled in 2000 at the University of South Carolina School of Public Health. You can find the complete list of more than 600 activities at its website.
Dancing--ballet or modern, twist, tap, or jazz = 4.8 MET
Fishing--from riverbank, standing = 3.5 MET
Carrying groceries upstairs = 7.5 MET
Making beds = 2.0 MET
Interpret these numbers as "fishing from a riverbank burns three and a half times as many calories as sitting still in a chair," or, "ballet dancing uses more than twice the calories of making beds." To convert METs to calories burned by an activity, simply multiply RMR by MET. For instance, if Sam carried groceries up stairs for 15 straight minutes, the calories he used would be the product of his hourly RMR, the MET of carrying groceries upstairs, and the time he spent doing it: 89 calories/hour x 7.5 x .25 hours = 167 calories.
Total Daily Calories
Armed with your resting metabolic rate and activity factors for your daily activities, you can now combine them to find your total daily caloric expenditure. To do this, you will need to account for your activity level for all 24 hours of the day, and then add them up. Here is an example using Sam's activities for one day:
Sleeping: 0.9 MET x 8 hours = 7.2 MET
Showering, grooming: 2.0 MET x 1 hour = 2 MET
Household chores: 2.5 MET x 2 hours = 5 MET
Working at his desk: 1.8 MET x 7 hours = 12.6 MET
Cleaning his gutters: 5.0 MET x 1 hour = 5 MET
Power Lifting at the gym: 6.0 MET x 1 hour = 6 MET
Reading, talking, eating: 1.5 MET x 3 hours = 4.5 MET
Watching TV in bed: 1.0 MET x 1 hour = 1 MET
His entire day adds up to 43.3 MET, so his total calories burned for the day = 89 x 43.3 = 3,854 calories.
Caveats
As you study this technique, please keep in mind that all of these tables, equations and processes were derived from statistical means and confidence intervals, so they will not apply to everyone. If you suffer from a chronic illness, autoimmune disorder or metabolic disease, or you are an unusually fit person, an elite athlete, or are extremely under- or over-weight, they may not be a good fit for you. For most people, however, these calculations provide an excellent means of determining our daily activity calorie-burning.
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