To actually measure the amount of body fat, there are accurate but cumbersome techniques that are not readily available to most physicians. An indirect method of estimating body fat has been developed that is easy to use and replicate, and can be used to track fat weight gain or loss over time. This measurement is called the Body Mass Index (BMI), and is calculated by taking body weight in kilograms (kg) and dividing it by the square of height in meters (m2), or in equation form:
BMI = Weight (kg)/ Height squared (m2)
If one measures BMI in pounds (lbs) and inches (in), this calculation becomes:
BMI = Weight (lbs) x 703/ Height squared (in2)
An individual is defined as having a healthy weight if their BMI is between 18.5-24.9 kg/m2. If their BMI is between 25.0 and 29.9 kg/m2, then they are considered to be overweight. If the BMI is greater than 30 kg/m2, then they are considered as being obese. There is even a sub-categorization of obesity into mild (BMI 30-34.9 kg/m2), moderate (BMI 35-39.9 kg/m2), and severe (BMI greater than 40 kg/m2). The easiest way to figure out your BMI is to use a BMI table such as the one reprinted below. Where do you fall on that table in terms of normal, overweight and obese?
Table of BMI as Compared to Weight and Height in kg/m2
BMI Measurement in kg/m2
18.5 or less Underweight
18.5-24.9 Normal
25.0-29.9 Overweight
25.0-29.9 Overweight
30.0-34.9 Mild Obese
35.0-39.9 Moderate Obese
40 or greater Severe Obese
50 or greater Super Obese
50 or greater Super Obese
There are caveats to using BMI as an estimation of total body fat content, and one has to put BMI measurement into clinical context. For example, a bodybuilder may have a large muscle mass that contributes an inordinate amount to their overall body weight. Elevated weight due to extra muscle mass will lead to a higher BMI that might fall in the obesity range based on calculation of weight divided by height squared. However, professional bodybuilders are clearly not obese. Before you think that you are not overweight based on this description, please look in the mirror. If you think you look like the Incredible Hulk, but your silhouette more closely resembles a Bartlett Pear or the Pillsbury Doughboy, then you probably don’t qualify for the bodybuilder exemption! Let’s take another less obvious example, an individual who is 6’3” tall and weighs 218 pounds. This person’s calculated BMI is 27.2 kg/m2, which according to the BMI table falls in the overweight range. I don’t think anyone would consider National Football League wide receiver Terrell Owens as being overweight, but he is listed at 6’3” and between 218-223 pounds with 5% measured body fat.
However, for the most part, BMI is a useful tool to estimate and track the average person’s level of “over-weightedness”. So why is BMI important to calculate when dealing with excess body fat? This whole business of weight, obesity, co-morbidities, and cardiovascular disease is a matter of balancing risks and risk factors. It has clearly been documented that having a BMI greater than 25 kg/m2 due to extra body fat increases ones risk for certain medical problems and premature death. The risk increases slowly as BMI increases until a level of 30 kg/m2 is reached. Above that point, the risk of significant cardiovascular disease and early death significantly increases. Why is that? Having a BMI greater than 25 kg/m2 increases one’s likelihood of suffering from hypertension, sleep apnea, high cholesterol level, diabetes, and a whole host of other medical problems. Some of these co-morbidities increase one’s risk for significant cardiovascular disease and heart artery blockages, leading to an increased chance of for fatal as well as non-fatal heart attacks as well as early death. The higher the BMI, the higher the risk for cardiovascular disease and death, particularly above a BMI of 30 kg/m2. Does everyone with high blood pressure, high cholesterol or diabetes die at an earlier age than their counterparts who don’t have these conditions? Not necessarily so, but the chances are higher that one will die earlier if one has these problems due to obesity. That is why your internist, family doctor, or cardiologist is pushing the so called Statin drugs such as Lipitor and Pravachol, when your total cholesterol level is only slightly elevated, or even in the normal range, but you had heart disease at an early age. People don’t like taking Statin drugs because of the potential side effects of muscle pain or liver damage. However, these medications have been shown quite clearly to lower the risk of recurrent heart attacks and even death in high risk populations. In fact, it has recently been demonstrated that patients without what is termed a “q-wave” on their EKG at the time of their heart attack did as well with medical management with Statins and other medications as with aggressive treatments such as angiography and coronary artery angioplasty.
Now an individual with a BMI less than 25 kg/m2 can still suffer from high blood pressure, diabetes, or high cholesterol. These people also have an increased risk for heart disease, stroke, and death independent of their body weight. Often, this population has a very strong family history of heart disease and heart attacks at an early age, or a long history of smoking cigarettes. But in general, people with a BMI greater than 25 kg/m2 have a higher chance of having the medical co-morbid conditions as compared to people with a BMI less than 25 kg/m2. These co-morbidities subsequently increase the risk of cardiovascular disease such as heart attacks, congestive heart failure, and death.
Another marker for extra body fat is the waist circumference. Waist measurement is made just above the pelvic bone on the side, not at the level of the belly button. This measurement is shown in the illustration below.
However, for the most part, BMI is a useful tool to estimate and track the average person’s level of “over-weightedness”. So why is BMI important to calculate when dealing with excess body fat? This whole business of weight, obesity, co-morbidities, and cardiovascular disease is a matter of balancing risks and risk factors. It has clearly been documented that having a BMI greater than 25 kg/m2 due to extra body fat increases ones risk for certain medical problems and premature death. The risk increases slowly as BMI increases until a level of 30 kg/m2 is reached. Above that point, the risk of significant cardiovascular disease and early death significantly increases. Why is that? Having a BMI greater than 25 kg/m2 increases one’s likelihood of suffering from hypertension, sleep apnea, high cholesterol level, diabetes, and a whole host of other medical problems. Some of these co-morbidities increase one’s risk for significant cardiovascular disease and heart artery blockages, leading to an increased chance of for fatal as well as non-fatal heart attacks as well as early death. The higher the BMI, the higher the risk for cardiovascular disease and death, particularly above a BMI of 30 kg/m2. Does everyone with high blood pressure, high cholesterol or diabetes die at an earlier age than their counterparts who don’t have these conditions? Not necessarily so, but the chances are higher that one will die earlier if one has these problems due to obesity. That is why your internist, family doctor, or cardiologist is pushing the so called Statin drugs such as Lipitor and Pravachol, when your total cholesterol level is only slightly elevated, or even in the normal range, but you had heart disease at an early age. People don’t like taking Statin drugs because of the potential side effects of muscle pain or liver damage. However, these medications have been shown quite clearly to lower the risk of recurrent heart attacks and even death in high risk populations. In fact, it has recently been demonstrated that patients without what is termed a “q-wave” on their EKG at the time of their heart attack did as well with medical management with Statins and other medications as with aggressive treatments such as angiography and coronary artery angioplasty.
Now an individual with a BMI less than 25 kg/m2 can still suffer from high blood pressure, diabetes, or high cholesterol. These people also have an increased risk for heart disease, stroke, and death independent of their body weight. Often, this population has a very strong family history of heart disease and heart attacks at an early age, or a long history of smoking cigarettes. But in general, people with a BMI greater than 25 kg/m2 have a higher chance of having the medical co-morbid conditions as compared to people with a BMI less than 25 kg/m2. These co-morbidities subsequently increase the risk of cardiovascular disease such as heart attacks, congestive heart failure, and death.
Another marker for extra body fat is the waist circumference. Waist measurement is made just above the pelvic bone on the side, not at the level of the belly button. This measurement is shown in the illustration below.
Measurement of Waist Circumference
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