The InBody Band Knows If You're Secretly Fat

You may be able to fool the Body Mass Index, but you can't hide from the electrical impulse.

The InBody Band uses bioimpedance, which senses fat-to-muscle ratio based on electrical impulses rather than just averages. (Courtesy of InBody USA)

A lot of activity trackers can count steps, track sleep patterns, monitor heart rate from your wrist, and display calls and texts. The InBody Band does all that, too, but it can also measure your body composition. Read: it can tell you how fat or skinny you are.

Right now, we rely on the Body Mass Index to determine our ideal weight based on height. But it’s a crude metric. If you’re super fit but, say, a serious downhill ski racer, your quads and glutes are likely to be large and heavy, and that might tip the scales into the “overweight” category, according to the National Institute of Health BMI calculator.

That’s because BMI is based on averages, not individuals, says Jeff Kim, head of marketing for InBody. “It’s just a curve.” When you get to the edges of that curve—say a super trim, tall skier—the calculations fall apart.

The Band, on the other hand, works via bioelectrical impedance, the same way InBody’s deluxe devices work (those are more sophisticated, but the principle is the same). In essence, when you want to measure fat-to-muscle ratio, you tab through a menu on the watch and it sends out a low-level electrical impulse through your wrist. You then close the electrical circuit sent from the device by putting a few fingers on the Band with your other hand. More fat slows down the circuit, while less allows it to pass through our body more quickly.

The tech sounds simple, and has been used before in floor scales, but it's not infallible. Your hydration levels will affect the tech's accuracy, exercise physiologist William J. Evans, director of the Nutrition, Metabolism, and Exercise Laboratory at the University of Arkansas for Medical Sciences, told the Boston Globe. Sweating or drinking alcohol could affect results, he says. That said, other studies have shown that bioimpedance is a more accurate measure of body composition than the rough BMI chart, so it's a good start. 

Kim says there’s value in this data, especially since there’s strong evidence that you might stay thin as you age, but, especially if you’re an endurance athlete, you could be losing muscle mass. If you can test for that easily, then the theory goes that you could also correct against the loss by adding more weight-bearing exercises to your regime.

Perhaps what’s most compelling about the system is that it shows how these devices are becoming sharper than mere digital pedometers—and slowly but surely spitting out information that enables a proactive response to get you fitter.

Available in March for $179

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