You have probably heard the adage, "3,500 calories equals a pound of fat." This statement is true, in a laboratory setting, but not necessarily in the human body. The way the body uses and burns fat and calories is much more complex than what happens in a laboratory, however, there are still useful ways to calculate calorie burning and weight loss.
Step 1
Determine your body weight in kilograms. If you already know your body weight in kilograms, skip this step. Otherwise, divide your body weight in pounds by 2.2. For example, if you weigh 160 lbs., your weight in kilograms is 160 / 2.2 = 73 kilograms.
Step 2
Figure out how much fat-free mass (FFM) your body has, in kilograms. Multiply your weight in kilograms by [1 - your body fat percentage]. If you take the above example of 73 kilograms, and have a body fat percentage of 18 percent, then your fat-free mass in kilograms is 73 kg x (1 - 0.18) = 60 kilograms. Have your gym or personal trainer give you your fat percentage, or use an online calculator (see Resources).
Step 3
Calculate your resting metabolic rate (RMR) for 24 hours. While there are several good equations for calculating RMR, one with excellent predictive value is the Cunningham RMR equation: RMR = 370 + 21.6 x FFM. If you continue with the above example, you get RMR = 370 + 21.6 x 60 = 1,666 calories, which is the number of calories you burn in 24 hours, at rest, who has 60kg of fat-free mass.
Step 4
Convert your daily resting metabolic rate to an hourly rate by dividing by 24. In the above case, that would be: hourly RMR = 1,666 / 24 = 69.4 calories per hour.
Step 5
Find the metabolic equivalent task values (MET) for any activities or exercises you performed. You can find these values in the "The Compendium of Physical Activities", located at the University of South Carolina School of Public Health website (see Resources). Here are a few example MET values: running at 5 miles per hour, MET = 8; mowing the lawn, MET = 5.5; taking a yoga class, MET = 2.5.
Step 6
Determine the total number of calories you burned in these activities. Find the product of your hourly RMR, the MET for the activity, and the hours you spent doing the activity. For example, using our 60kg FFM person from above, assume she runs at 5 mph for 30 minutes, four times per week. The calories she burns running would be calculated as 69.4 x 8 x .5 x 4 = 1,110 calories.
Step 7
Calculate the pounds lost from the calories burned by dividing by 3,500. Continuing the above example of 1,110 calories burned per week from running, you would expect to lose 1,110 / 3,500 = 0.32 pounds per week, or about one pound every three weeks.
Tips and Warnings
- You can find RMR calculators online that will do the first three or four steps for you.
- All of the equations, tables, and calculations above are based on statistical averages and confidence intervals, so they may not be 100 percent applicable to your individual situation. If you suffer from a chronic illness or are unusually fit, this process may not give you accurate results. As your body weight or lean mass changes with weight loss or gain, you will need to recalculate the value of your resting metabolic rate. Also, the human body has an amazing ability to adapt to changes in intake and output, so the weight loss or gain results you get in the first few weeks of a new regimen may not be sustainable for the long haul.
Member Comments