Why should we measure body fat?
Whether you’re an athlete or completely new to exercise, finding out how your body carries muscle, fat, and bone can give you a starting point. Having these numbers can help you and your trainer establish targeted goals and measurable results. And knowing more about your body composition provides a more comprehensive picture than what a scale or your BMI can tell you. If your weight on the scale is the same or higher after several months of dedicated exercise and healthy eating, you might be concerned, but body fat testing might reveal that you’ve shed pounds of body fat and added pounds of muscle – a major accomplishment!
How do we measure body fat?
There are a number of ways to measure our body composition, and a wide range of cost, convenience, and accuracy. Here are some of the most common testing methods:
DEXA
How it works
DEXA stands for “Dual-Energy X-Ray Absorption”, and is a body-scanning machine that was originally developed to measure bone density. You simply lie on your back for 10-20 minutes while the machine takes x-rays. The machine distinguishes bone mass from fat mass from “fat-free mass” (muscle and other non-fatty tissue). DEXA scans predict visceral fat (the fat surrounding your organs) as well as subcutaneous fat (which lies under your skin). High visceral fat is linked to cardiovascular disease, so it’s helpful to know if you’re at higher risk. (Fortunately, regular exercise can reduce your visceral fat and risk of cardiovascular disease.)
Accuracy
DEXA scanning is extremely accurate, with a standard error of ±1.8%.
Cost
High – a single session could run $125-300 or more. DEXA scanning requires specialized, expensive equipment only located at some hospitals and clinics.
Dunk Tank
How it works
A dunk tank estimates body fat through water volume displacement. You get into a large tank of water and submerge yourself fully, expelling all the air from your lungs. The tank weighs you and your body fat is calculated based on estimated body density.
Accuracy
When conducted properly, this method can show highly accurate results with an error rate of about ±1.5%. A few big caveats, though: First, people with extremely low or extremely high body fat may not receive accurate readings. Second, accuracy depends on the client’s ability to blow all the air out of their lungs during a pre-test and the test itself. Because air makes the body float, clients who aren’t able to expel all their air will receive miscalculated percent body fat results.
Cost
On the higher end – a single test is around $49 and up.
Bod Pod
How it works
The BOD POD is a small capsule-like chamber you sit down in for a few minutes while the chamber measures the air volume. Similar to the dunk tank (but more comfortable), the BOD POD measures the volume of air displaced by your body to find relative fat mass and fat-free mass.
Accuracy
Very accurate – standard error falls between ±1-3.7%.
Cost
On the pricier side – a single session might run between $50-75.
InBody Testing
How it works
InBody testing uses a small machine that resembles a scale with handles and a small screen to enter information. It uses bioelectrical impedance – where the machine sends a minor electric current through the body – to measure body fat mass, dry lean mass, and total body water. (The results also show a breakdown of your total lean muscle in five quadrants, and can reveal imbalances between left and right sides.) Stand on the platform with your feet covering the metal electrodes and hold the handles, standing still for about a minute. The machine collects data, then prints the results to a sheet of paper.
Accuracy
Strongly accurate – InBody testing has shown to be 98% accurate against DEXA scanning.
Cost
Pretty affordable! At the Fitness Lab, it’s only $35 per test.
Bioelectrical Impedance Home Scales
How it works
You can purchase a bathroom scale that has electrodes to test your body fat at home using bioelectrical impedance. Although it’s the same basic method as the InBody testing, the equipment is less complex. Stand on the scale with your feet covering the metal electrode plates for a moment. The machine will give you a body fat reading once complete.
Accuracy
Home scales aren’t very accurate for measuring body fat, but they can provide you some baseline numbers – so if your numbers change next time you test, you’ll have something to compare your results to. It’s essential to test under the same conditions each time so your results are consistent and comparable.
Cost
These specialized scales run between about $60-80 at the lower end, and a few hundred for pricier options. It’s a one-time purchase, but you forgo having a trained person administer testing.
Calipers
How it works
Skinfold calipers are generally used as a quick, low-cost method of body fat testing.
The tester pinches several sites on the client’s body, and measures the skinfold thickness with the calipers, recording measurements in millimeters. The results are compared to a chart of norms by age and gender.
Accuracy
Moderate. Results can vary depending on the type of calipers used (for example, inexpensive plastic vs. high-quality metal). When conducted properly, this method can provide a good estimate (about ±3% error) – but because it’s easy to do improperly if you’re not having testing administered by a trained professional, it’s often better for clients looking for a ballpark figure. If you’re seeking a highly accurate reading, you may want to choose another testing method (or try an additional method and compare results).
Cost
Testing rates by a professional may vary. Your doctor or a gym may offer this service.
Which method should I choose?
Everyone’s needs are different – so if you’re an elite athlete, you may need extremely precise measurements; if you’re just beginning your fitness journey, you might just want a rough number. It all depends on whether your top priority in testing is accuracy, convenience, cost, or comfort.
Keep in mind that even if you’re using a method with a higher margin of error, staying consistent with the testing method and conditions can be illuminating. Ensuring that you follow testing protocol each time you’re tested (or at least getting tested under the same conditions you were last time) can give you much more precise results.
Whatever you choose, it’s smart to have your body fat tested when you’re beginning to work toward a goal – even if you feel a little uncomfortable! If the thought of having your body fat measured makes you feel vulnerable or embarrassed, that’s OK – but in three months or so, you might really wish you had those numbers! If you’ve been working hard, it can be incredibly rewarding to compare your starting point to where you are now. It’s a great way to track your progress, and many people are motivated by seeing their accomplishments on paper to stay on track and keep working toward new goals.