You may know that you are overweight and know how much you actually weight, but how “much” are you overweight? There are generally two ways to gauge how overweight you are: Body Mass Index (BMI) and Percentage Body Fat (PBF). These measurements are not necessarily in opposition. They can actually be used together. To be able to use these measurements, however, you should know what each measures and their respective advantages and disadvantages.
Body Mass Index (BMI) is widely used measurement for how overweight someone is. It is calculated by dividing body mass (in kg) by body size (m^2). The BMI scores are then classified based on their values. The below chart summarizes the various BMI scores and their classifications.
Normally, a BMI score of less than 18.50 connotes unhealthy underweight status.There is such thing as being too skinny which poses health risks just as serious as being obese. Any score above 30 suggests that you maybe obese. Of course, you should desire to be in the healthy range of 18.5 to 24.99. But don’t fixate on exact figures. Having a score of 25.50 is not the end of the world. In fact, as you will see later, it may not necessarily imply you’re overweight at all.
BMI is handy tool. All you need is your weight and height, and you have your number. I believe the BMI is useful measure for most people. This belief is backed by scientific studies that show moderate correlation between BMI and other more reliable measurements for body fat. And the reason for this correlation will make sense to you shortly.
For most people BMI is reliable measure of excess fat for a given size. However, for athletes and bodybuilders, BMI is not reliable. BMI is a blunt instrument: it assumes all people possess nearly identical muscle mass composition. We intuitively know that is not true. Take the case of two 6 ft men each weighing 240 lbs. However, one has only 8% body fact percentage and is all muscular, gym junkie. The other is a couch potato with 25% body fat percentage. Both of these men would have a BMI of 32.50 rendering both men as obese. Obviously, this is nonsense. The gym guy is in better shape as most of his weight is comprised of lean muscle mass whereas the coach potato dude has a lot less lean muscle mass. But the gym dude doesn’t represent the average man. That is why there is a moderate correlation between BMI score and actual body fat percentage.
Body Fat Percentage (BFP) is more accurate measure of body fat. Beyond that, the BFP informs about your overall fitness level. The lower your BFP, the fitter you are. Unlike the BMI, the BFP score incorporates your gender and age into its calculation. BFP eliminates almost all of the disadvantages of the BMI. Table 1 below shows a rough guide for BFP for women and men.
|Body Fat Classification||Men||Women|
Note that men have lower threshold for obesity and for essential fats than women. Essential fats are the bare minimum your body needs to function properly. So, while we want to shed fat, some of it is actually necessary for our bodies to function properly. Generally, for men, if you want to have six-packs you’ll need body fat percentage below 10%, maybe below 8%. The table shows BFP for different ages of both genders.
There are different ways to measure your Body Fat Percentage. For the average person, the best method is to purchase calipers. You can purchase them at most fitness stores. Some weight scales come with purported body fat percentage measuring capabilities. These scales send electrical impulses through your body and then measure the resistance. From this the instrument extrapolates your body fat percentage. The problem is there are a lot factors that can affect the resistance the electrical signal meets. How much water you have in your body, how dirty/clean you feet are, the last time you ate… all affect the reading you get. That is why I prefer using the calipers.
Your body fat percentage, once obtained, can be very help with your weight loss goals. First, you can use it to set a target. If you are obese, there is no point in setting an immediate or intermediate target of 10% body fat. You better off setting a more realistic goal of 15% against a current 25% body fat. Needless to say, you need to have a concrete plan in place delineating how you will reach your target goal. Second, once you reach your target, you need to set a realistic “range.” Reality is your body fat percentage will fluctuate. By setting a target, you can maintain a healthy weight using deviations from your target range as a reminder for greater vigilance. Your body fat percentage can also tell you if you need to pack some place. You might be of those “skinny fats,” people have weight normal person weight but are in fact carrying too much fat. The BFP will tell you if you are carrying too much fat.
To recap, use the BMI to get a crude estimation of your body fat. Use the Body Fat Percentage to get a more accurate measure of how much fat you’re carrying. Once you know how much excess fat you’re carrying, devise a plan to shed the excess weight.