While there are a lot of online charts and tables and websites that will calculate your daily caloric intake and body mass index for you, it is also possible to calculate these values yourself to develop a set of personalized measurements that are tailored to your lifestyle and habits.
Body Mass Index
The first step to figuring your appropriate daily caloric intake is to calculate your body mass index (BMI). The body mass index is a rough measure of body fatness that relates weight to height. While it is a historically popular measure, because of its simplicity, the BMI should be considered with caution, since it does not perform well in situations where there is an unusually high or low level of body muscle, water or bone density. That said, the calculation for BMI is fairly straightforward: BMI = (weight in lbs) x 703 / (height in inches)^2. The results for BMI are categorized like this: BMI less than 18.5 is considered underweight; BMI between 18.5 and 24.99 is considered normal; BMI between 25 and 29.99 is considered overweight; and BMI greater than 30 is considered obese.
BMI Examples
Here is an example of this calculation for Sam, who is 6-foot 1-inch and weighs 180 pounds: BMI = (180 x 703) / (73^2) = 23.7, which is in the normal range. Now suppose Sam began a weight lifting program that added 15 pounds of muscle to his frame. By any accounting, Sam would be healthier and in better shape at 195 pounds than he was at 180, due to the additional lean body mass, but the BMI calculation of (195 x 703) / 73^2 now puts him at 25.7, which is at the low end of the overweight range. This is an example of when the BMI would not be a great tool for assessing health risk.
Resting Metabolic Rate Calculation
The next step in predicting a healthy daily caloric intake is to find your resting metabolic rate (RMR). RMR is the number of calories you burn when completely at rest. RMR can be accurately measured using an expensive clinical process known as "indirect calorimetry," or can be estimated using a number of different regression equations developed through research. One such set of equations, with a remarkable degree of predictability, was produced by Kelley Martin, R.D., M.P.H., and her team at the Medical University of South Carolina in 2004.
In addition to BMI, the equations developed by these researchers take the following inputs: race, defined as white = 0, black = 1; diabetes status index (DSI), defined as normal = 0, pre-diabetic = 1, frank diabetic = 2; and lean body mass (LBM), which is weight in pounds x (1 - body fat percentage). If you don't have your body fat percentage handy, you can get it from a trainer at a gym, a nutritionist or use an online calculator to estimate it.
These are the equations:
Women: 803.8 + 0.3505 x Age x (BMI - 34.524) - 135 x Race + 7.21 x LBM + 50.90 x DSI
Men: 909.4 + 0.3505 x Age x (BMI - 34.524) - 135 x Race + 7.21 x LBM + 9.1 x DSI
Example RMR Calculation
Continuing with Sam from above, let's add that he is a black male, 43 years old, with normal, healthy blood sugar, and 9 percent body fat. The RMR for Sam would be calculated as follows:
1) Sam's LBM = 180 pounds x (1 - 9%) = 164 pounds
2) Sam's RMR = 909.4 + 0.3505 x 43 x (23.7 - 34.524) - 135 x 1 + 7.21 x 164 + 9.1 x 0 = 1,794 calories
Thus, Sam's resting metabolic rate, the number of calories he burns when he is sitting in a chair for 24 hours is 1,794. That would be 75 calories per hour.
Activity Calories Calculation
The next step in the process is to figure calories burned in activity. The modern way of doing this is to use a concept called MET, or metabolic equivalent task. METs are numbers like 1.3, 6.8 or 12.5, which give us the relative intensity of an exercise, compared to rest. You can find an extensive list of MET values in "The Compendium of Physical Activities" at the University of South Carolina School of Public Health website. Here are some example METs from the list: ballet or modern dance, 4.8 MET; fishing from a riverbank, 3.5 MET; carrying groceries upstairs = 7.5 MET.
Interpret these numbers as "ballet dancing burns 4.8 times as many calories as sitting still in a chair." To convert MET values to the calories you use in an activity, simply multiply together your hourly RMR, the MET value of the activity and the hours engaged in the activity. For instance, if Sam went fishing from a riverbank for three hours, the calories he used in that time would be: 75 calories/hour x 3.5 MET x 3 hours = 788 calories.
Total Daily Calories
To calculate the calories you use in a day, and therefore, the caloric intake you require, add up all the activities you do in 24 hours in this same fashion. Here is an example done with Sam's activities for one day: sleeping, 75 x 8 hours x 0.9 MET = 540; showering and grooming, 75 x 2 hours x 2.0 MET = 300; working at a desk, 75 x 7.5 x 1.8 MET = 1,013; doing household chores, 75 x 2 hours x 2.5 MET = 375; power lifting at the gym, 75 x 1 hours x 6 MET = 450; reading, talking and eating, 75 x 2.5 hours x 1.5 MET = 281; watching TV in bed, 75 x 1 hour x 1.0 MET = 75. That adds up to 24 hours, and the calories burned for the whole day are 3,034.
Final Words
If you follow this technique, keep in mind that these equations and processes are derived from statistical means and confidence intervals, so they don't apply to everyone. As we saw, if you fall outside the norm in terms of musculature, bone density or some other measure, you may not fit well into these equations. For most people, however, these calculations provide a useful means of calculating body mass index and daily caloric intake needs.
Member Comments