Measurements of Body Composition

Body Weight and Body Mass Index

The body mass index is one of the most important numbers you will collect to build out your personal database.  This is because there are very well-established guidelines that tell you where you stand, and the information is easy to collect.  The body mass index is simply a way of normalizing your weight based on your height. 

To measure body mass index, you only need a good bathroom scale.  Ideally, you have an accurate digital scale, but most scales will do.  Many digital scales now link to mobile phone applications via blue tooth.  This can be a good way to keep track of your weight and watch it over time.  If you are buying a new digital scale, try to get one that also measures your body fat percentage, which I will cover in the next section.

To calculate your body mass index, take your weight in kilograms and divide by the square of your height in centimeters.  If you are using pounds, feet, and inches, you simply multiply the output by 703, so the equations to calculate body mass index are shown below:

·       Metric:  Weight (kg)/Height (meters)2

·      Imperial:  Weight (lbs)/Height (Inches)2 * 703

As an example, a person who was 6 feet tall and weighed 188 lbs would be 1.829 meters tall and would weigh 85.275 kg.  So, to calculate the body mass index you would divide 85.275 by the square of 1.829 or 3.34.  The result would be 25.5.  This is a body mass index just over the line between the normal range and overweight.  If that same person weighed 178 lbs or 80.739 kg, the body mass index would be 24.17.  This body mass index is in the normal range.

Ø  Weigh yourself on a reliable scale and then calculate your body mass index.  Enter the result in your notes or field journal.

Body Fat Percentage

Weight and body mass index is a useful metric because it is easy to measure and calculate and it makes it easy to compare people with varying overall height.  But a far more useful metric is to measure body fat percentage.  Body mass is comprised largely of body fat and muscle.  So, its possible to have a high body mass index but have a very healthy body with a good muscle to fat ratio.  It is also possible to have a low or normal body mass index but have poor muscle mass and thus a high body fat percentage.  We see this often in older individuals.  This is why the best measure of a healthy body composition is to directly measure the body fat itself and calculate the body fat percentage.

To measure body fat, the simplest way is to use a bathroom scale that does it.  Although this method is not perfectly accurate, we find that the ease of doing it outweighs the need for perfect accuracy.  If you are able to obtain such a scale, simply follow the instructions to measure your percent body fat.  Bathroom scales that measure body fat, use a process called bioimpedance.  You stand in bare feet on the scale and grip sensor electrodes in your hands.  It sends an imperceptible electric charge from your feet through to your hands and uses it to estimate the body fat.  Commercially available scales that use bioimpedance are available in many doctors’ offices and gyms. They are much more accurate than bathroom scales and are a second way to get an accurate measurement of body fat percentage. Some of the commercially available scales also measure muscle mass which can be useful too.

Body fat percentage can also be measured using skin fold thickness measurement.  This is a relatively easy way to do it and some of our patients use this method, but it can be difficult to do on yourself and you need to learn the technique so that you do it accurately.  To measure skin fold thickness, you need a caliper that measures the distance between the prongs of the caliper accurately.  These calipers are available online and range from simple plastic tools all the way up to more sophisticated digital devices.  You simply pinch the skin between your fingers and then place the caliper over it to measure the thickness of the fold.  There are several excellent videos online for how to measure skin fold thickness.

One final way of measuring body fat percentage that you should be aware of is to use a DEXA scan.  This is the same machinery that is used to measure bone density.  Some DEXA machines are configured to measure body composition.  It is a low risk and a very accurate way to measure body fat percentage and if you have access to it, we do recommend that you measure body fat this way.  This is the most accurate way of measuring muscle mass as well.  This is particularly useful for older individuals who are at risk of losing muscle mass over time.  The table below shows the acceptable ranges for body fat percentage.

Men
Age	20–29	30–39	40–49	50–59	60 –69	70-79
Very lean	4.2–6.4	12.5–14.9	9.5–13.0	11.1–14.9	12.0–16.1	13.6–15.5
Excellent	7.9–10.5	12.5–14.9	15.0–17.5	17.0–19.4	18.1–20.2	17.5– 20.2
Good	11.5–14.8	15.9–18.4	18.5–20.8	20.2–22.3	21.0–23.0	21.1–22.9
Fair	15.8–18.6	19.2–21.6	21.4–23.5	23.0–24.9	23.6–25.6	23.6–25.2
Poor	19.8–23.3	22.4–25.1	24.2–26.6	25.6–28.1	26.4–28.8	25.7–28.0
Very poor	25.1– 33.7	26.4–34.4	27.7–35.2	29.2–36.4	29.8– 37.2	29.3–37.3
Women
Age	20–29	30–39	40–49	50–59	60 –69	70 –79
Very lean	11.4–14.1	11.0–13.8	11.7–15.2	13.8–16.9	13.8–17.7	13.7–16.4
Excellent	15.2–16.1	15.5–16.5	16.8–18.2	19.1–20.8	20.1–22.0	18.8–21.2
Good	16.8–20.0	17.5–21.0	19.5–23.6	22.3–26.6	23.2–27.5	22.6–26.3
Fair	20.7–23.5	22.0–24.8	24.6–27.4	27.4–30.0	28.3–30.8	27.1–30.0
Poor	24.4–28.6	25.8–29.6	28.3–31.9	30.7–33.8	31.5–34.4	30.9–33.6
Very poor	30.9–38.4	31.4–39.0	33.4–39.0	34.9–39.8	35.4–40.3	35.0–40.0

Decide how you will measure body fat percentage throughout the experiment.  Then measure it and enter the percentage at the start of your experiment in your notes or field journal.

Waist Circumference

Body fat is more important than body mass index and may be the most important measurement in the entire experiment.  But not all body fat is created equal.  It turns out that some types and locations of body fat are more harmful than others.  When it comes to your metabolism, abdominal fat is the most harmful type of body fat.  We can estimate abdominal fat by simply measuring the waistline.  The waist circumference (belt size) is also an easy test to do.  Simply get a measuring tape and put it around your waist at the belly button.  Then put the tape around your hips so that you can measure the waist to hip ratio.  Just like BMI, waist to hip ratio is a good way to compare people of overall different sizes with respect to abdominal fat.  The higher the ratio the more abdominal fat you have and the greater your risk. 

When the waist to hip ratio is greater than 1 for men or .85 for women, it means that your body has the apple shape as opposed to a pear shape where the weight is carried lower.  Women generally carry more weight below the waist so their acceptable values for the ratio are lower than men.  The apple shape is considered the least healthy shape and most likely to lead to heart disease.

Measure your waist circumference using a measuring tape around your waist and then measure your waist to hip ratio.  Enter both values in your notes or field journal.

Muscle Mass

There are 2 readily available ways to measure muscle mass and numerous ways to estimate it. To measure muscle mass directly, the 2 readily available methods are BIA (Bio-Impedance Analysis) and DEXA (Dual-Energy X-Ray Absorptiometry) scanning. The BIA method uses an electrical charge to estimate muscle mass throughout the body. It is relatively easy to do and reasonably accurate as long as you use a machine that has been properly calibrated as you would find at a doctors office and in some fitness gyms. The DEXA method is much more accurate especially at extremes of height and weight. We use the DEXA method regularly on all of our patients, but most of you performing this experiment will not have ready access to it. If you do, we recommend using it as your gold standard for muscle mass.

Once you have your muscle mass calculated, we recommend calculating the skeletal muscle index using the following method:

1. Take the muscle mass in kg of the 4 limbs (the appendicular mass).

2. Divide that by the square of the height in meters.

3. This is called the skeletal muscle index or SMI.

An SMI of 5.5 for women or 7.0 for men is considered a sign of low muscle mass and is the main criteria used to diagnose Sarcopenia (the condition of low muscle mass). We try to maintain our female patients above 6 and our male patients above 7.5 at all times. Many of our patients well exceed this.

Measure your muscle mass and enter the value in your notes or field journal. Calculate your SMI and enter that value next to your muscle mass.