Calculate Your Own Energy Needs

Oftentimes, we over or underestimate how many calories our bodies require per day.  It’s difficult to figure this out because our energy needs vary on a daily basis, depending upon activity level.  Dietitians will plug in height, weight, age and gender into certain equations in order to figure out Basal Metabolic Rate (BMR),  a measurement of how many calories the body burns at rest.  There are a few different equations that can be used, as well as numerical coefficients for general caloric ranges.

The Harris-Benedict equation for BMR:

  • For men: (13.75 x w) + (5 x h) – (6.76 x a) + 66
  • For women: (9.56 x w) + (1.85 x h) – (4.68 x a) + 655

The Mifflin-St. Jeor equation for BMR:

  • For men: (10 x w) + (6.25 x h) – (5 x a) + 5
  • For women: (10 x w) + (6.25 x h) – (5 x a) – 161

Where: w = weight in kg, h = height in cm, a = age

This does not take activity into account, and so the final number needs to be multiplied by an activity factor of 1.2-2, depending upon how active the individual is.

~sedentary (little or no exercise) = BMR x 1.2

~lightly active (light exercise/sports 1-3 days/week) = BMR x 1.375

~moderatetely active (moderate exercise/sports 3-5 days/week) = BMR x 1.55

~very active (hard exercise/sports 6-7 days a week) = BMR x 1.725

~extra active (very hard exercise/sports & physical job or 2x training) = BMR x 1.9sunlight

Coefficients for Caloric Ranges:

In a clinical setting, we use coefficients to make it easier and faster to calculate ranges for patients.  For normal weight (BMI between 18.5-24.9), the coefficient is 25kcal/kg – 30 kcal/kg.  For overweight to obese, one can either decrease the coefficient to 20-25kcal/kg or create an ADJUSTED BODY WEIGHT (ABW) and multiple the ABW by a normal coefficient, 25-30kcal/kg/body weight.  For underweight individuals, or those with hypermetabolic needs, the coefficient can be as high as 30-35 kcal/kg of body weight.

It’s necessary first to find out what your IDEAL BODY WEIGHT (IBW) is, which is not necessarily an ideal body weight FOR YOU, but just a general reference +/- 10% based on gender and height.  It is usually on the low side, and so adding 10% is recommended and still within normal limits.

To find an IBW:

1.  Take your height in inches and convert it to centimeters (conversion factor: 2.54). Example, 5’5″ = 65inches.  65 x 2.54 = 165.1cm.

2. Calculation:

For women, it is 100 pounds for the first 5 feet, and 5 pounds per every inch over 5 feet.  Clearly, this is low if you are on the muscular side.

For men, it is 106 pounds for the first 5 feet and another 6 pounds per every inch over 5 feet.  Muscular men will need to factor in at least +10%.

So then, a 5’9″ male’s ideal body weight (+/- 10%) would be: 100 + (9 inches x 6) = 154 pounds. Remember that extra 10%, 154 lbs + 15.4 = 169.4 pounds, which is a nice ideal body weight.

To find an ABW:

The adjusted body weight (which is a body weight that becomes a goal weight in overweight and obese cases, and the one we use to calculate caloric needs), the formula is: current body weight  – ideal body weight =  “X.” Then, take “X”  x  .25 = “Y.”  Then, take “Y” + ideal body weight  = adjusted body weight.

EXAMPLE:

Let us use our example male of 5’9″ above. Let’s pretend his name is Kevin, he’s 28 and overweight with a current body weight (CBW) at 200 pounds.

200 (CBW) – 154 (IBW) = 46.

46 x .25  = 11.5.  11.5 + 154 (IBW) = 165.5

(note: this is very close to just adding 10% to his IBW).

Now lets divide 165.5 by 2.2 to get Kevin’s adjusted body weight in kilograms. This would be: 75.2kg.

For a kcal range per day, we multiply Kevin’s adjusted body weight in kilograms by 25 for the lower range, then 30 for the upper. Here is his kcal range:

1880 – 2256 kcal/kg/adjusted body weight

For protein range, we multiple his adjusted body weight in kilograms by 0.8 for the lower range, and the 1.2 for the upper.  Here is his protein range in grams/day:

60gms – 90gms/kg/adjusted body weight

For fluid needs in mL, just multiple his current body weight (in kg–> 200lbs = 91kg) by 30 for the lower and then 35 for the upper (it’s important to stay within the fluid range, too). So this would be:

2700mL – 3150 mL/kg/CBW per day. (This is roughly equal to 13 cups per day)

Now let’s compare our range to the Mifflin St-Jeor range to see how accurate we are (we are still using his ABW, since we do not want Kevin to maintain his weight, but rather, lose it):

For Kevin, the Mifflin equation states that his needs would be: (10 x 75.2kg) + (6.25 x 175.3cm) – (5 x 28years) + 5 = 1712kcal/day, which, when we apply an activity factor of sedentary (little or no exercise) = 1712 x 1.2 = 2054, which is right in the middle of the range we supplied for him above (1880 – 2256).

Now that we know our estimate is in line with the Mifflin equation, let’s see if it is appropriate for healthy weight loss.  Using the Mifflin equation, let’s plug in his CBW of 90kg.  Kevin needs 2140kcal/day to maintain his weight.  For him to LOSE 1lb per week, we need to subtract 3500 kcal/week from his diet, since 3500 kcal = 1 pound.  2140- 500kcal/day = 1640.  1640 is close to the lower range that we deduced (1712), meaning that we would recommend around 1700 kcal/day for Kevin to lose 1 lb per week.

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