Determining Daily Caloric Needs With the Harris Benedict Equation

dig deeperI had never really worried about counting calories before Insanity, but since I’m working out almost daily I need to make sure I get the right number of calories. I used the Harris Benedict Equation to find out what my calorie intake should be. I first came across it in the Elite Nutrition book that comes with Insanity but have since read about it in several places. If you’re interested in going right to the source, J. Arthur Harris and Francis G. Benedict published the paper A Biometric Study of Human Basal Metabolism about their findings in 1918 which is archived and free to view here.

Basically, the Harris Benedict Equation calculates your BMR (basal metabolic rate), which is the amount of calories you’d need if you were completely sedentary, and then multiplies it by your activity level to determine your caloric needs, or how many calories you need to consume per day. One thing that is mentioned elsewhere but not in the Elite Nutrition book is that the lack of accounting for lean mass means the equation will over estimate your needs if you are overweight and under-estimate them if you are very muscular.

The first step is to find your BMR. Men and women must use a separate equation. The number you arrive at is how many calories you need to maintain your current weight without exercising.

For women: 655 + (4.35 x Weight in Pounds) + (4.7 x Height in Inches) – (4.7 x Age in Years)

For men: 66 + (6.23 x Weight in Pounds) + (12.7 x Height in Inches) – (6.8 x Age in Years)

If you use metric measurements, the numbers to use for the above portion are a little different and can be found here.

Whichever method you used above, you multiply the number you got by your activity level according to the following list:

Sedentary-Little to No Exercise- 1.2
Lightly Active-Light Exercise (1-3 days a week)-1.375
Moderately Active-Moderate Exercise (3 to 5 days a week)-1.55
Very Active-Hard exercise (6 to 7 days a week)-1.725*
Extremely Active-Hard daily exercise and/or a physical job-1.9

*The Elite Nutrition book says 1.7 but everywhere else has said 1.725 so this is what I would use.

Generally, if you are doing Insanity you would pick Very Active, but if you’re not doing it daily you might use Moderately Active. If your goal is to maintain your weight while exercising, then this number is the number of calories to consume per day.

Now, if you want to lose or gain weight, this is where information starts to differ. The Elite Nutrition book says to subtract 500 calories a day if you want to lose weight and add 250 to 300 calories a day if you want to gain weight. Several other places such as advise adding 500 calories a day if you want to add about a pound a week.

To show you the Harris Benedict Equation in action, I’ll give you my calculations.

655 + (4.35 x 120 pounds) + (4.7 x 67 inches ) – (4.7 x 27)= 1365 calories to maintain weight without exercise.

Since I am doing Insanity 6 days a week it’s 1365 calories x 1.725 = 2355 calories (rounded up to the nearest decimal). Because I currently want to maintain this weight, this is the number of calories I’m shooting for. If I decide I want to develop muscle beyond that, I’d need to gain weight so I’d add 250 to 500 calories and need 2605 to 2855 calories per day.

If your weight, goals, or activity level change then you may need to recalculate your needs. Make sure to keep up with it so your body gets all the calories you need. Of course this advice is not intended to substitute advice from your doctor and/or nutritionist and is not a complete picture of what is required for proper health. But now that you know about the Harris Benedict Equation and how to use it, I hope this will give you a starting point to understanding your daily caloric needs.

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