When looking to figure out how your body is burning calories, you need to determine the minimum amount it needs to keep your heart beating, your lungs breathing, your body temperature normal, and so on – when you are doing absolutely nothing! This is known as your resting or basal metabolic rate (your BMR). It’s not something you just walk into a doctor’s office or lab and have done. But you should know how to calculate your resting metabolic rate.
First you have to fast for a full twelve hours. This is done to insure that your digestive system is at rest, that it’s completely inactive. Next, a full eight hours of sleep, and you sleep at a slight incline. This takes stress off of key points of your body. Thus your body is rested, relaxed, and you’re feeling no stress. Finally, just to be sure you are truly calm, the measurements are normally taken in a darkened room.
Formulas for Calculation
When it comes to the actual calculations, there are two formulas typically used. There is the Harris-Benedict equation, and then the Mifflin equation. It’s been found that the Harris-Benedict is not entirely accurate when used by people who are very young, very old, or rather overweight. So, keep that in mind when reviewing the number it gives you.
In terms of the actual formulas, they differ for men and women, and are as follows:
For Harris-Benedict, a man’s BMR is found by multiplying his weight in kilograms by 13.75, adding it to five times his height in cm, subtracting the product of his age times 6.76, and then adding sixty-six.
For a woman, the structure of the formula is the same, but the factors are different. It is 9.56 times her weight in kilograms, then add 1.85 times her height (also in centimetres), subtract 4.68 times her age, and add 655.
With the Mufflin equation, it also differs by gender, and is as follows:
A man’s BMR is equal to ten times his weight (still in kg), plus 6.25 times his height, subtracting five times his age, and adding five.
For a woman, the formula is the same, except for the last factor. Instead of adding five, you subtract 161.
This does make it a very easy formula to use under and circumstance.
Things to Think About
Now, there are some other things to consider when using these calculations. As stated above, extremes of age and body build can adversely affect the results. Plus, you also need to remember that muscle mass burns a lot of calories; whereas, fat burns much less. So, if you are particularly lean and muscular, your BMR will be substantially higher than the formulas indicate. Conversely, being overweight will result in a lower number.
To get just a rough calculation of your BMR, go online and do a search using that abbreviation. It’s so common, you’ll get a number of websites that have a calculator available; some even use imperial/English units rather than metric. Merely type in your age, height, sex and weight, and it’ll give you a rough metabolic number. While not perfect, it’s at least a starting point.
Image: Miles Kelly Art Library, Wellcome Images, Creative Commons License