The Harris Benedict Equation
and Katch Mcardle Equation

The Harris Benedict equation and the Katch McArdle formula are two different ways of measuring BMR (Basal Metabolic Rate). That is the rate at which you use up energy when at rest and is explained fully here:

What is BMR?

As explained in What is BMR the Harris Benedict equation offers a way of calculating your BMR approximately, and the web page also explains some factors that can affect the BMR such as gender and weight. The page also explains the Total Daily Energy Expenditure (TDEE) and how the BMR can be used to calculate that).

The Harris Benedict equation and Katch McArdle both take these into account, although the Katch McArdle equation also takes your percentage body fat into account because weight made of fat rather than lean muscle will use less energy when at rest than will muscle tissue.

The page above also provides information on several other factors that affect the BMR and you can perhaps also take these into account in assessing the results of your calculations if you believe that they apply to you.

Once you have established your BMR

Here are the two equations and how to apply their results:

THE HARRIS BENEDICT EQUATION

The calculation takes your gender into account, and also height, weight and age. It is different for men and women.

Women: BMR = 655 = + (9.6 x Kg weight) + (1.8 x cm height) - (4.7 x age in years)

Men: BMR = 66 + (13.7 x Kg weight) + (5 x cm Height) - (6.8 x age in years)

Conversions:1 inch = 2.54 cm1 pound = 0.455 Kg1 foot = 12 inches1 stone = 14 pounds

For Example:

You are a woman You are 5'4" tallYou weigh 8 stone 3 poundsYou are 34 years old

Using the Harris Benedict equation:

5'4" = 64" = 162.6 cm (to nearest 0.1 cm)11 stone 1 lb = 115 lb = 52.3 Kg ( to nearest 0.1 Kg)

BMR = 655 + 502 + 292.7 - 159.8 = 1290 Calories/day

TDEE Calculation

You can now calculate your TDEE. To do that, you need a multiplier factor to apply to your BMR. That depends on an approximated description of your daily activity:

Sedentary (very little exercise + sedentary job): BMR x 1.2

Lightly Active (light exercise, walk or sports up to 3 days/week): BMR x 1.375

Moderately Active(moderate exercise, jog or sports 3- 5 days/week): BMR x 1.55

Very Active(Frequent exercise, jog or sorts 6-7 days/week): BMR x 1.725

Extremely Active (Daily hard exercise, hard physical work, Hard sport): BMR x 1.9

You are the woman above but have started jogging daily and work as a teacher. You are moderately active

Your TDEE = 1.55 x 1290 =2000 (to nearest whole number)

THE KATCH MCARDLE EQUATION

If you know your lean body mass or body fat percentage, you can get an even more accurate result. The Harris Benedict equation already has a factor included in this, from the gender factor, because women generally have a higher body fat percentage and lower lean body mass.

Because the Katch McArdle equation treats these differently, only one equation is needed for both men and women. Basically:

BMR = 370 + (21.6 x lean body mass Kg)

So, you are male or female, weighing 155 pounds (70.5 Kg) as before.You have a body fat percentage of 22% (=11.5 Kg fat and 40.8Kg lean)

BMR = 370 + (21.6 x 40.8) =370 + 881 = 1251 (nearest whole no.)

Your TDEE = 1.55 x 1251 = 1939

That is a difference of 61 Calories per day: very close to the Harris Benedict equation result. This woman was chosen because she is at a healthy weight for her age and height, though on the low side of perfect. The difference between the two gets closer as the woman gets nearer the mid-point for her statistics, and larger as she gets heavier.

Thus, the Harris Benedict and the Katch McArdle results are close for people who have a healthy BMI, but becomes greater one way or the other as they become lighter or heavier. This is due to the reduced or increased lean muscle in the two.

The Katch McArdle calculation is more accurate than the Harris Benedict equation, and should always be used if you know your lean muscle mass or body fat percentage. It becomes more significant when people tend to being too low or too high a weight for their size and age.

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