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A better BMI calculator- Katch-McArdle formula


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Excerpt: Someone just raised the question of basing their fatloss routine on their estimated BMR figure. There are a lot of factors that determine how many calories a day our bodies consume just carrying out their critical processes. The most common BMR calculators don't even attempt to measure many of these factors, but as you might expect, the more of these factors a formula could correctly integrate, the more accurate it's caloric consumption estimate would be. An estimate that I first read

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  1. #1
    Da Pope RottenWillow's Avatar
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    A better BMI calculator- Katch-McArdle formula

    Someone just raised the question of basing their fatloss routine on their estimated BMR figure.

    There are a lot of factors that determine how many calories a day our bodies consume just carrying out their critical processes. The most common BMR calculators don't even attempt to measure many of these factors, but as you might expect, the more of these factors a formula could correctly integrate, the more accurate it's caloric consumption estimate would be.

    An estimate that I first read years ago, and has always stuck with me since, is that our bodies need something like 600 additional calories every 24 hours for every 10 pounds of skeletal muscle we add to it. Since LBM then is a substantial factor in determining our BMR, and subcutaneous bodyfat is fairly easy to estimate, any BMR calculator worth a crap should include this important data, right?

    Well one of them does. The Katch-McArdle formula. Below is a cut and paste of a basic explanation of this formula.




    Katch-McArdle formula (BMR based on lean body weight)

    If you have had your body composition tested and you know your lean body mass, then you can get the most accurate BMR estimate of all. This formula from Katch & McArdle takes into account lean mass and therefore is more accurate than a formula based on total body weight. The Harris Benedict equation has separate formulas for men and women because men generally have a higher LBM and this is factored into the men's formula. Since the Katch-McArdle formula accounts for LBM, this single formula applies equally to both men and women.

    BMR (men and women) = 370 + (21.6 X lean mass in kg)

    Example:

    You are female
    You weigh 120 lbs. (54.5 kilos)
    Your body fat percentage is 20% (24 lbs. fat, 96 lbs. lean)
    Your lean mass is 96 lbs. (43.6 kilos)
    Your BMR = 370 + (21.6 X 43.6) = 1312 calories

    To determine TDEE from BMR, you simply multiply BMR by the activity multiplier:

    Example:

    Your BMR is 1312
    Your activity level is moderately active (work out 3-4 times per week)
    Your activity factor is 1.55
    Your TDEE = 1.55 X 1312 = 2033 calories



    Activity Multiplier list

    Sedentary = BMR X 1.2 (little or no exercise, desk job)
    Lightly active = BMR X 1.375 (light exercise/sports 1-3 days/wk)
    Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)
    Very active = BMR X 1.725 (hard exercise/sports 6-7 days/wk)
    Extr. active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X day training, i.e. marathon, contest etc.)

  2. #2
    Olympian Rachel...lol's Avatar
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    Re: A better BMI calculator- Katch-McArdle formula

    I wrote an article with that info in it a while back - we use diff words but looks the same
    1. Because most of us are not completely sedentary throughout the daily, the Basal Metabolic Rate needs to be adjusted for the amount of activity performed in an average day. The resulting number is called your Total Calorie Needs. This calculation, based on the Harris Benedict Equation simply chooses a factor to multiple your BMR:
    If you are sedentary (little or no exercise) – BMR x 1.2
    If you are lightly active (little exercise/sports 1-3 days weekly) – BMR x 1.375
    If you are moderately (active moderate exercise/sports 3-5 days weekly) – BMR x 1.55
    If you are very active (hard exercise/sports 6-7 days weekly) – BMR x 1.725
    If you are extra active (very hard exercise/sports & physical job or training twice daily) – BMR x 1.9
    Continuing with our example, a moderately active woman with BMR of 1,620 would have Total Calorie needs of 2,511. This number represents the amount of calories that can be consumed daily to maintain current weight of 200lbs, assuming that moderate activity level is maintained.
    2. The next step is determining the appropriate calorie deficit necessary to reach a weight loss goal. There are approximately 3,500 calories in a pound of body fat, so creating a 3,500 calorie deficit through diet, exercise, or a combination of both, would equate to losing one pound of body fat. (7,000 calories equals 2lbs, etc). Using a weight loss goal of 20 pounds in 3 months, our example tells us that a daily deficit of 835 calories must be achieved per day. The breakdown:
    20lbs in 12 weeks is equal to 1.67lbs per week
    multiply lbs per week (1.67) x 3,500 (calories in a lb) = 5,845
    determine daily deficit by dividing days of the week = 5,845/7 = 835

    3. The last step is to formulate your plan. You can achieve your weight loss goal one of three ways
    i. If you plan to reach your goal based on adjustments to your diet alone, simply subtract your daily deficit from your Total Calorie needs to determine your allotted calorie consumption for the day. Using the earlier example subtract 835 from 1,620 equates to daily calorie consumption of 785. Using this method obviously is not appropriate, as The American College of Sports medicine (ACSM) recommends that calorie levels do not drop below 1,200 per day for women, and 1,800 for men.
    ii. If you plan to reach your goal through exercise alone, without adjustments to your diet, then 835 calories daily must be burned on top of the exercise being performed before undertaking the program. Remember, the Total Calorie Needs was based on a previously established moderate activity level.
    iii. Using a combination of diet and exercise allows you to be flexible in creating a plan that fits with your lifestyle. For example, burn an extra 500 calories through an intense cardio session, and then reduce your calorie intake by 335 calories on that day will result in achieving your established deficit.

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