6 Methods of Measuring Body Fat and Their Pros and Cons

Hydrostatic Weighing

How it Works

Hydrostatic (or underwater) weighing is a form of estimating body fat percentage in which a person is completely submerged in a pool of water. “You sit on a special scale in the water, submerge your whole body including your head, exhale completely to decrease lung volume so the body floats as little as possible, and then the density of the body is measured,” says Richard Weil, M. Ed., CDE and Director of the Weight Loss Program at Mt. Sinai St Luke’s Hospital. “That value is plugged into an equation to estimate body fat. Fat floats and that’s the principle.”

Pros

According to the NSCA Essentials of Personal Training, the standard of error in other methods of estimating body fat such as skin fold assessment, bioelectrical impedance, and anthropometric measures are established against HW and these methods may have more error than HW. HW was formerly the most trusted body composition testing method up until the Bod Pod came into play. Now, it’s up for debate.

Cons

Some people might feel uncomfortable exhaling all of the air from their lungs while underwater, although it is performed in shallow water. The tank must be emptied and cleaned after each weighing, thus it takes longer to perform several tests in a day compared to a Bod Pod. “We consider the costs of UWW greater than the value,” says Weil.

Bod Pod

How It Works

The Bod Pod is an egg shaped device that measures body volume and body weight to determine body density and body fat. First, you step on an electronic scale outside of the device which measures your weight. Then, you measure the air pressure of the Bod Pod without you in it. Next, step into the chamber and let the machine measure the air pressure with you in it.

These values will give you the volume of the empty Bod Pod and the volume of the pod with you inside. Subtract these two numbers and you’ve got your body volume. Divide your weight by your volume and you’ve got your density. The software uses density to estimate body fat.

Pros

We tried a Bod Pod and it only took a few minutes to complete two testing trials. The results are printed immediately and you also get your resting metabolic rate (RMR) and total energy expenditure estimates (TEE). Recent research, such as this 2003 European Clinical Journal of Nutrition study and this 2002 American Journal of Clinical Nutrition study shows that the Bod Pod is safe and accurate for body composition analysis.

“BodPod is very accurate when compared with HW,” says Weil. “Depending on the population measured, the error can be as low as 1-2 percent.”

Cons

Since the procedure was so carefree, it’s hard to point to any negative aspect. There are certain things you must do in order for the rest to work properly.

“The Bod Pod is very sensitive to baggy clothing so you have to wear clothing that is form fitting and doesn’t have cotton in it because cotton traps air and the air compresses differently,” says Christopher Dunbar, PhD, MPH, CCEP, RCEP, FACSM.

“You also have to measure lung volume. Some people use the Bod Pod and they don’t do the lung volume measurement they just estimate lung volume from a person’s height, weight, gender and so on. There you lose some accuracy.”

Dual Energy X Ray Absorptiometry (DEXA)

How It Works

In a DEXA scan, you lie down and receive a scan of your body composition and bone mineral density. DEXA systems use a source that generates x-rays at two energies to estimate bone mineral content and soft tissue composition.

Pros

According to Capital Blue’s Medical Policy, DEXA’s accuracy is up to par with other forms of analyzing body composition. Also, with DEXA, you find out exactly where your fat is located; it can actually tell you the amount of belly fat you have.

“One of the benefits of DEXA is you can get the regional distribution,” says Dunbar. “You can see where the fat is,” says Dunbar.

Cons

DEXA scans expose you to radiation, and although this 2006 American Journal of Clinical Nutrition study calls the amount you receive in one test “low,” radiation is radiation.

“I don’t know if DEXA for body fat is ethical given the radiation,” Dunbar says. Finding a place that offers DEXA scans for body composition might take some digging. M&F reached out to New York University and Brooklyn College, and both institutions don’t offer DEXA for body composition.

Skin Calipers

How It Works

Skin calipers are the most accessible method in determining body fat percentage. A technician uses the device by pinching a layer of skin to get any underlying fat. Sites that are measured are: triceps, pectoral, abdominal, supriliac, and thigh. There are two steps to determining body fat percentage: body density and using body density to estimate body fat. The body density equation was developed for each by Dr. Andrew Jackson and M. L. Pollock. As for the fat percentage equation was created by Siri (1961) and Brozek (1963).

As mentioned before, skin calipers are easily accessible, making them a huge pro. Registered dietitian-nutritionist, Katharine Wagner, recommends, “The user should aim for an average of three readings, selecting 3-7 sites on the body for accuracy. A benefit of using skin calipers is that it gives you a bigger picture of the subcutaneous fat/visceral fat. Too much of this fat can lead to metabolic syndrome.”

Cons

Skin calipers require a lot of accuracy, and usually the technician has to go through rigorous training to be certifiable to use one. As for the formulas don’t vary with individuals, they remain constant. This can lead to false results, adding more fat to a lean, ripped physique.  

Body Fat Scales

How It Works

Body fat scales are also called bioeletrical imedance scales, which is quite similar to a normal scale. The only difference is that there are electrodes under your feet or where you places your hands on the hand-held device. A small electrical impulse gets sent through the body, and the rate of the impulses are measured. Lean tissues conducts electrical impulses quicker than fat.

Pros

The scales are affordable and most gyms have the hand-held device. Both devices only require you pressing a button, making it user-friendly. 

Cons

Accuracy is the biggest down fall of this method because readings can be impacted by hydration levels, meal times, and workouts.

BMI and Waist-to-Hip Ratio

How It Works

Body mass index is away of measuring body fat that’s based on height and weight. It’s one of the oldest methods in the books because it’s a simple calculation. Another method is waist-to-hip ratio, which gets determined by the use of a measuring tape. Using the measuring tape, measure the circumference around the widest part of your buttocks and then around your waist. Once you get both measurements, divide your waist measurement by your hip measurement. 

Pros

Each method requires a simple calculation. Katharine Wagner says, “The waist-to-hip ratio gives a better picture of subcutaneous fat/visceral fat on a person. It’s also easier to use than skin calipers.”

Cons

Accuracy is another issue for the two methods. Katherine says about BMI, “It doesn’t tell the difference between muscle and fat. Hence, muscle weighs more than fat—giving an inaccurate measurement.”

What’s The Best?

Based on the recent literature, it’s the Bod Pod and HW. It’s important to consider more than just accuracy, but consistency. How often can you really get to a Bod Pod? Even though calipers and body fat percentage scales may not be as accurate, they provide a way to know if you’re gaining/losing body fat. At the end of the day, that’s the most crucial knowledge.

“As far as I understand, the Bod Pod and HW are about as accurate a method as you’re going to get,” Dunbar says. “It’s just a question of one’s easier to do.”