The monitor calculates the speed at which the current travels through body tissue. The result is a digital display of body fat percentage and weight of body fat in 7 seconds. Most body fat readings are taken by using a caliper that literally measures the rolls of body fat. But several alternative body fat monitors work by sending a weak electrical current through the body. Both devices claim to take accurate fat readings by relying on an arcane technique called bioelectrical impedance analysis.
Water is the biggest ingredient in our bodies, followed by fat.
To get an independent fat measurement, I went to Bodies in Motion in Santa Monica for a time-tested caliper fat test. My health club trainer Sean took plastic calipers and pinched my back, upper thigh and waist to measure the rolls of fat under my skin. I'm middle-aged, so those figures seem ridiculously out of reach. If I wanted a more accurate fat test, my next step would have been to dunk myself in a pool. Some folks insist on a hydrodensitometry reading because it offers the most precise fat measurements.