Today's topic is BMI, BMR, and BFP, three numbers that each have something to do with health and fitness. They are often confused, for obvious reasons. My hope is that by the end of this post you'll be able to distinguish the three numbers, figure out how to calculate them for yourself, and then apply them to your healthy life!
BMI (Body Mass Index)
BMI is a formula that was created around the turn of the 20th century; it yields a number which is a ratio between two simple numbers: your height, and your weight. It has nothing to do with your body composition, your age, your gender, your metabolism, or inches around your waist. This is still how doctors determine if you are overweight or obese. 25 is the magic number - if your BMI is over 25, you are considered overweight and if your BMI is over 30 you are considered obese. Obesity is a medical condition by this standard - one you can even get a handicap sticker for.
Since BMI is easy to measure, it is still the basis by which the CDC tracks obesity trends in America. The truth is, it's a pretty good rough gauge of your body fat. The one reason it isn't the best way to track health is that it doesn't compare the amount of muscle and fat in your body, like BFP (see next section) does. Because of this, some pro athletes or bodybuilders like Body Beast creator Sagi Kalev have BMI's well over 25. Realistically, these individuals are quite healthy, and this formula is flawed because it can't recognize the amount of muscle they have on their body. Realistically, the average guy like you and me doesn't have the problem of having too much muscle, so staying under 25 should still be a priority. However, if you are a "fit" person you might find your number is right near 22-24, and that is ok. Bottomline: aim for under 25, but know it's a very rough measurement. If you are under 18.5, you are likely underweight and should be eating more, that is pretty much true for anyone that low!
To calculate, go here: http://www.nhlbisupport.com/bmi/.
BFP (Body Fat Percentage)
For many, Body Fat Percentage is a more accurate gauge of health. As the name implies, it is the ratio of the amount of fat in your body to your entire mass, or literally the percentage of fat in your body. The remainder of your mass is muscle, bones, connective tissue, fluids, and organs.
The problem with BFP is it is nearly impossible to calculate 100% accurately. There are a few ways to estimate. First, is the body fat caliper method. Some of the programs you have, like TurboFire, come with a caliper. By pinching a layer of fat on specific parts of your body, you follow a chart that comes with the caliper to estimate the amount of fat on your body. Here is a site that has several ways to take measurements and calculate: http://www.linear-software.com/online.html. Notice it is different between male and female. It is important when pinching yourself with the caliper to get a layer of skin and fat to get an accurate measurement.
Additionally, there is a military formula that takes into consideration neck, waist, and height (and hips for women). This formula is called the "tape measurement method" on the link I sent above.
Some scales have a feature that can estimate body fat, but this is probably the most inaccurate.
If you really want to know, there is a water displacement test you can have done professionally that gives the most accurate reading. I think the most important thing is to find a measurement that works for you, and stick to it so you can track your results. Ultimately, the size of your waist is very much related to body fat %, especially for men, so tracking loss of inches on your waist is also a great way to track.
For men, in general a six-pack is under 10% body fat, a flat stomach is 15%, and under 20% is recommended. For women, a six-pack is under 15% body fat, a flat stomach is 20%, and under 25% is recommended. Women naturally have more body fat for the purpose of child bearing.
BMI is easy to calculate, but is a very rough measurement. It is easy to track since doctor's offices record it at physicals.
BFP is much more telling as to your overall health, but is harder to calculate, and almost impossible to get 100% accurately. Find a method that works for you and continue to use it for consistency. If you really want to track your results when doing a workout program like P90X, Insanity, or TurboFire, track BFP not BMI.
BMR (Basal Metabolic Rate)
BMR is not a way to track your resuls, it is rather (and simply!) the amount of calories your body burns per day. Your Basal Metabolic Rate is basically the number of calories you would burn if you laid in bed for 24 straight hours and didn't exert any energy except the amount that keeps you alive - your basic metabolic functions and brain activity. I include it here because the acronym is so similar to BMI, it is often confused!
Knowing your BMR is essential understanding the amount of calories you need per day. The truth is, the number of your BMR is often way higher than you think. You can calculate it here: http://www.bmi-calculator.net/bmr-calculator/. Note that this is the amount of calories you burn BEFORE daily activity, like taking the stairs, standing on your feet, playing sports, and certainly excercise.
What do you do with this number? You can estimate the amount of calories you burn in a day. Say you have an active job, you might burn an additional 300 calories during your work day. Say you workout, you might burn an additional 350 calories in one hour. With all the walking in your day, you might burn 200 calories while you are awake. This is a conservative estimate if you are an active person, and I just added 850 calories of activity that you just burned, on top of your BMR! The moral of the story is you probably need to eat more than you think if you are working out. If you need more help figuring this out one-on-one, hit up the contact page.
So - remember your three letter B acronyms - BMI, BFP, and BMR. Note that BFF has nothing to do with health, unless your BFF is your workout buddy!