|I am notoriously known for making the simple complicated; after all, it is a lot more fun that way. After one month and few hundred research articles extending from the 1960’s to 2006 I have done it again. Only this time, I have learned how to make it simple. But don’t worry, I promise to show you why measuring body fat is a lot more complicated that it appears at first blush.
Here is all you need:
- Height and weight,
- waist and hip circumference,
- and for the really motivated you can optionally include skin fold thickness of the triceps, subscapular, suprailiac, and midthigh regions.
That’s it. You’re done.
Ok, I can’t leave you hanging. Let me tell you why these measurements are part of the Formula For Life.
GENDER: Hopefully an obvious measurment. A mans body is different from a womans.
HEIGHT: Here at least is one measurement that we can count on never changing, or can we? As a child, we grow bigger. As an adult, we stay the same, that is until we get a little older and start to shrink. At least this is a slow process. But we need our height to compare our weight, and other measurements, to the general population. Two hundred pounds on a 6 foot 2 inch man may be the perfect weight, but a tad much on a 5 foot woman.
WEIGHT: The measurement we are all concerned about. Luckily we can measure this pretty accurately. The best way to do this is in the morning after an overnight fast, before you eat, after going to the bathroom, and without cloths. Make sure your scale is calibrated, but even if it isn’t it should provide an accurate measure of change in body weight.
Hold it, the change in body weight. This is where it can get complicated. What does the change in body weight (mass) really tell us? If a person weighed 150 pounds last week and 148 pounds this week, have they lost 2 pounds of fat? After all, this is what we want to know isn’t it? The answer is maybe – but probably not.
You see, the body is a marvelously complicated machine. For purposes of this discussion imagine the body divided up into two compartments, the fat mass (FM) and the fat-free mass (FFM) such as muscle and bone. For a more detailed understanding of the body compartments click here. When you lose and gain weight both of these compartments change. If you lose weight by just diet you lose FFM. If you lose weight with only exercise you lose FM and gain FFM (it is true that with exercise the scale may not move, but your clothes are loser – you lose fat predominately from the abdomen area).
So here is the beginning of the complications and the subject of hundreds if not thousands of research articles on this one subject. How do you know how much fat you lost? You don’t. There is no perfect method of measuring FM loss.
WAIST/HIP CIRCUMFERENCE: There are basically (again everything is more complicated than it appears, but lets assume) two different types of fat on the human body – visceral fat (VAT) and subcutaneous fat (SAT). VAT is the fat deep in the abdomen under the skin. SAT is the fat attached to the skin. The visceral fat is the fat that is responsible for the majority of health problems associated with obesity – diabetes, high blood pressure, and heart disease. The only way to fairly accurately measure VAT is with an MRI or CT scan of the abdomen. Not very cost effective. The next best measure of abdominal fat is our waist. The simple measurement of our waist circumference turns out to be the best predictor of VAT, and of potential health problems.
The hip circumference is actually a fair measure of health protection in women. For the same waistline, as the hip size goes up there is less risk of health issues. Nobody knows why, it is just an observation at this time. Also, this only appears to work in women, sorry guys it does not seem to work for us.
SKIN FOLD MEASUREMENTS: While the waist circumference is the best predictor of VAT, skin fold measurements can be a good measure of SAT, after all this where SAT resides. Fortunately this is one area where less is actually better. Many, many research papers have been written that looked at various combinations of several sites to measure skin folds. They all seem to find that using just 3 or at most 4 sites is the most accurate measure. Here are the sites and some reasoning behind them (my thoughts at least). The triceps, subscapular, suprailiac, and midthigh.
My thoughts. First, the sites come from the literature so choosing the sites was not my decision. But here is why I agree with them. The purpose of these measurements is to determine SAT and SAT is everywhere on the body. The triceps provide a measure of fat on the arms. The subscapular provides a measure of fat on the torso (and appears to be the most consistently used site in the literature). The midthigh is a measure of fat on the lower extremity. Finally, the suprailiac is a measure of hip fat, although if you measure your hip circumference you might eliminate this site.
WHAT ABOUT EQUATIONS AND FORMULAS FOR BODY FAT
So, now you want to make life complicated. Obviously I thought long and hard about this and in the various sections describing BMI, circumference, skin folds, BIA, DXA, and other research measurements I do include many equations predicting percent body fat (%BF). But they all do just one thing, they predict body fat, they don’t measure body fat. And, because they predict instead of measure, none of them are totally accurate and can have errors from as little as 1-2% to as much as 20% or more.
The measurements I have provided above are simple, repeatable, and fairly reliable. They do not require any special equipment that most homes don’t already have (except the skin fold calibers) and very little training is required. However, there are couple equations that you might want to include only because there is so much research using them.
- BMI. This simple measure has been with us forever and has been shown to predict various degrees of health related problems. Most of the newer literature has found that if you use the waist circumference, then there is no longer any predictive value from using the BMI.
- WHR. The waist to hip ration has been with us a long time just like the BMI. It is a measure of central obesity (big belly) and has been linked to health related issues along with an increasing BMI. Also, for women, we are beginning to realize that a larger hip (with a small waist) does have health benefits. So, I will list it for that reason.
- Tanita scale. While not an equation, you may want to use the %BF predicted from this scale along with your measurements. If you do, please be sure to read the section on BIA and understand the limitations of this measurement. I include this only because it is relatively inexpensive, you need a scale, and many people already have them.
WE ARE DONE
Here is your final list of measurements and a few calculated results together with how often you should measure them. With these measurements you will know if you are making progress or not, even when the bathroom scale seems frozen in time.
- Triceps, subscapular , iliac, and midthigh skinfold – every 1-2 months. Add all the skin fold measurements together for one large comparative number.
- Tanita scale %BF – monthly.
- Bioelectric impedence %BF if available – every 1-2 months.