On Fitness: Making Sense of My Body Fat

What does it mean that a fancy device says my arm is 30.7 percent fat?


Staff writer Sarah Baldauf.

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My right arm, apparently, is 30.7 percent fat. I know this because I recently tested the latest in souped-up bathroom scales, the Tanita Ironman InnerScan, model BC-558, which retails for about $300. I learned a few other stats about myself after stepping atop the foot pads and grasping the retractable "hand electrodes," which briefly sent a low-level electrical current through my body. My left arm, slightly leaner than its counterpart, packs 26.6 percent fat. I'm more symmetrical on my bottom half, carrying an even 33 percent fat in my right leg and 32.9 percent in my left. My trunk totes around 29.3 percent fat, while my overall body fat is 30.5 percent. Strangely, I'm also 33 years old in metabolic terms, according to the increasingly sinister-looking device. Hmm, that's curious. My parents say I was born in May of 1976, making me 31. Deep breath.

As a consolation, perhaps, the InnerScan gave me a "visceral fat rating" of 3, which the scales' chart classifies in the "healthy" range of 1 to 12. Anything between 13 and 59 means I "should consider making lifestyle changes," according to the pamphlet that comes with the scale. Visceral fat wraps itself around abdominal organs and promotes diabetes and cardiovascular risk. Maybe I don't have to worry about a deadly gut, but the idea that nearly a third of me is comprised of that gnarly globular yellow stuff is certainly disappointing, if not gross.

I reflexively rejected the unfavorable numbers and made a trip to Royal Fitness & Nutrition in Bethesda, Md., to get a second opinion of sorts, which involved a scientifically respectable body-composition measuring tool: the Bod Pod. While I sat inside a sealed, egg-shaped pod for a few minutes, wearing a bathing suit and swim cap, the machine measured how much air my body displaced and used that volume to determine my overall fat. The Bod Pod is used mostly in research studies at universities, at hospitals, and in certain health clubs that can afford the pricy machine. For me, Royal Fitness was kind enough to waive the $59.99 nonmember fee, but my happiness wore off as soon as I got my results: 30.4 percent overall body fat—just one tenth of a percentage point off the InnerScan's result. Damn. Double damn.

A series of desperate questions flashed through my mind: Do the 30 to 45 minutes of running I do three or four times a week mean nothing? What about the 4-mile round-trip bike ride I take to work every day? Or all the veggies, fruit, sushi, and whole grains I eat? Sure, I'll have the occasional burger and fries, and I do adore cheese, but I rarely drink soda and never have fast food. "Why don't you just give up now?" suggested a cynical coworker. Ugh. Not quite yet. I needed context. I'd obtained a novel stat, but was the newfound knowledge of any use?

"Well, it doesn't improve your health," says Christine Gerbstadt, a spokeswoman for the American Dietetic Association and a practicing physician and dietician. For most people, she says, body mass index is a perfectly reasonable basic measure of health. BMI is that trusty ratio of weight to the square of height used as a general indicator of body fatness, though it offers no specifics on body composition. At 5 feet, 7¾ inches and 141 pounds, my 21.6 BMI score falls in the "normal" range (between 18.5 and 25.9), according to the Centers for Disease Control and Prevention's BMI calculator.

Gerbstadt hasn't seen Tanita's latest InnerScan model, but she says that such high-tech bathroom scales—those that use electrical currents to measure body composition—can give misleading results. Even a little overhydration or dehydration can skew results, and getting separate measurements of each limb is of questionable value, she says.

So, I wondered, is there any value to submitting myself to the mockery of these home scales? "For some people it can be very helpful and reinforcing if they're making changes to improve health," she says. But it shouldn't be used more often than every 12 weeks, she added, because day-to-day fluctuations in body composition results have no significance. To bring my percentage of fat down, I would have to build muscle mass. Such sinewy tissue burns more calories than body fat, even at rest.