August 2, 2019
On a hot, sunny Manhattan Monday morning, I found myself on the Upper West Side in a bathing suit and swimming cap. But rather than jump into a pool, I slipped instead into a BOD POD — an egg-shaped machine that would tell me what percentage of my body was made up of fat.
Body composition testing — also called body fat testing — has long played a role in medical research and weight-loss studies. But over the last decade or so, biohackers, athletes and science-minded fitness buffs have begun to test their own body makeup, determining what percentage of their volume comes from fat, versus muscle, bone, blood and other matter. Now, I was doing the same — frozen still inside the vessel as the machine measured the amount of air displaced by my mostly-bare body. I held perfectly in place for two 30-second measurements, then breathed a big sigh of relief as the machine unsealed itself.
By Tuesday, I had my results from Fitnescity, which connects consumers to available testing equipment nationwide, then crunches the numbers. After testing my body mass and providing my age (28), weight (110 pounds) and height (5 feet 2 inches), I learned that I have 23.8 percent body fat, which puts me in the 25th percentile of women who have taken tests through Fitnescity. I landed on the bottom edge of the company’s “moderately lean” category, which, given my love of yoga but the aversion to all things cardio, was not much of a surprise. As I scrolled through all the details of my inner workings, I found myself wanting to know more. Would my body fat percentage change if I took up running, for example? Had a child? What percentage of my non-fat mass was bone? Muscle? I was hooked, and I was not the only one.
A body fat testing lab.Anthony Weller/View/Shutterstock
“We have different types of users,” says Laila Zemrani, founder and CEO of Fitnescity. “The obvious ones are athletes — people who need to perform at their best. If they don’t measure [their body fat], then it makes it a little bit difficult.” Boxers, for example, often need to land at a certain weight by fight night and want to be sure they are only shedding fat. “In the weeks leading to an event, you have to make sure … you’re [cutting weight] in an optimal manner since you can’t lose all your muscle. You have to measure, to know you’re the best you can be,” she says. BOD PODs, like the one I used, are popular in professional locker rooms and sports combines, while some athletes use full-body scans called Dual-energy X-ray absorptiometry (DEXA) scans, to make sure they do not have more fat on one side of the body than the other, which can lead to muscle overuse and injury.
On the other side of the spectrum are those with chronic conditions or obesity, who monitor their body fat to check on weight loss progress, and to ensure that the pounds being dropped are not all muscle. But a growing percentage of body composition testers are curious members of the general population who want to know more about their bodies, says Zemrani. People, I realized as I crunched the numbers, like me.
“Don’t aim for a number. Aim for a lifestyle.”
There is a strange sense of understanding that comes with seeing your physical body broken down into data points. Like any millennial woman, I have stared at my body in mirrors and photos for longer than I care to admit. But something about the numbers brings rationality to it, helps me to step outside of myself and take stock of things.
My reaction is not uncommon. “It’s a booming market,” says Zemrani. “Before, it was a little harder to come across these kinds of things. Now, there’s a general desire to know as much as you can about your own body — to be in control of your own data.” She credits tests like 23andMe with sparking people’s curiosity and unlocking an appetite for information. Many clients now test regularly, monitoring their body fat throughout new exercise regimens or diets in order to track their progress. “It’s eye-opening,” says Zemrani. “It’s [got] a cool factor.”
Still, David Berman, M.D., a physician and founder of appointment-booking site Slingshot Health, says that body composition testers should stay focused on the bigger picture. “One index by itself can be very misleading,” he says. “You could have a [low level of body fat] and be so unhealthy. If you use body fat composition in addition to your weight, in addition to your resting heart rate, in addition to blood tests, it will serve you better than one test in isolation.” Plus, he says, some body fat tests can vary based on hydration levels, how much you have eaten, your body hair and more, just like weight can fluctuate throughout the day. For best results, look for a test site where results are analyzed by a trainer or research specialist and pre-test guidelines are provided.
Berman also cautions that people can fixate on their numbers, trying to get to a certain percentage, rather than getting to a certain level of health. “Don’t aim for a number,” he advises. “Aim for a lifestyle.” The percentages can be a good indicator of whether your exercise and eating habits are working for you, and unlocking your body’s information can be a great motivator, but it is just one piece of the puzzle.
Below, our guide to the tests:
BOD POD
Many machines are based in hospitals and research labs — the one I used was located at Mount Sinai St. Luke’s Hospital, which opened it up to use by third parties such as Fitnescity. It is a moneymaker for the hospitals, which need the $30,000-and-up machines for their own uses, and allows consumers to use prohibitively expensive machinery at a bearable ($145 in NYC) price.
BOD PODs are about as accurate as you can get, says Zemrani, using your weight, height, age, gender and body volume as determined by the machine to spit out a body fat percentage. “When you enter the chamber, the air is displaced,” Zemrani explains, which determines your body volume. “From body volume, your body fat mass can be calculated with pretty good accuracy.”
The test requires stripping down to a spandex bikini or sports bra/shorts combo, slipping a shower cap over your hair, removing any jewelry, then sitting absolutely still inside an egg-shaped machine for 30-second bursts of time. Claustrophobics beware: The machine is a tight fit, and you can sense the air being pulled out of the machine while you breathe silently. All in all, though, it was a seamless experience, and results arrived in just over 24 hours.
DEXA SCAN
DEXA scans work by taking a snapshot of the body to reveal where fat lies. The scan can also test bone density, which is critical for aging patients. When it comes to body fat, the tests have been found to be slightly more accurate and comprehensive than density-based tests like the BOD POD. DEXA scans are also slightly pricier than BOD PODs, — they run around $200 in the NYC area, though they are sometimes covered by insurance when prescribed for bone density testing.
HYDROSTATIC
Hydrostatic weighing is the most involved method of body composition testing, but it is also one of the most accurate and time-tested. Users hop into a small, deep pool, sit on a stool fully submerged in the water, then exhale all the air out of their lungs. Someone can then calculate how much air was displaced, compare that to body weight and height, and come up with a body fat percentage based on volume. Those wishing to get wet can look to their local universities and hospitals for hydrostatic testing locations, where testing will cost upwards of $50.
CALIPERS
Body fat tests bring to mind a set of pinchers? Those are called calipers, and work by measuring the amount of subcutaneous fat (aka the stuff just below the skin) trapped between the two sides of the contraption. That amount is then calculated with a host of other numbers to give you a body fat percentage that is typically somewhat accurate, but open to fluctuation. Your doctor may be able to give you a caliper test, as could a personal trainer. You can buy and use the tool on your own for around $10, but you are better off outsourcing.
INBODY
Hop on the body of the InBody scale, grab the two handles, and hold on for a minute or two. Currents that run through your body will test body fat percentages, along with muscle strength and reserved water, while the scale portion takes your weight. You will end up with a number that is nearly as accurate as hydrostatic tests and can prove helpful when tracking weight loss. No need to schlep all the way to a hospital, either: The machines are increasingly common at upscale gyms, such as Lifetime Fitness and Equinox, as well as boutique studios like F45 Training. Your health club membership should give you free access, as would a gym day pass.
BIOELECTRICAL IMPEDANCE ANALYSIS
Bioelectrical impedance analysis machines, or BIAs, are certainly the easiest testers, but they are also the least accurate, as they can be tripped up by hydration levels, recently-eaten food and other factors. “It’s not completely useless,” says Zemrani. “If you use it over time, every day, you can sort of seeing a trend, even though one day might be off.” You can find BIAs, which use a weak electrical current to detect fat and muscle mass, at many gyms, but if it is accurate numbers you are after, you might consider looking elsewhere.