A calculator for body fat

Tanita Family Body Fat Monitor/Scale: The user programs age, gender, height and activity level (from inactive to athlete) into the machine, which sends a small electrical current through the feet.

The current travels at different rates through water and fat-free mass than it does through fat, and the measure of that current determines the amount of body fat. The technique, called bioelectrical impedance analysis, is safe, says the company, but cautions that people with pacemakers or other implanted medical devices should not use it.

While body fat monitoring can be a good way to get and stay fit, Dr. David Heber, director of the UCLA Center for Human Nutrition, says machines marketed to consumers may not be sufficiently calibrated. And the technique may not render a precise body fat measurement, he says. “It’s not going to hurt you,” Heber says, “but you can also use other methods to calculate body fat, such as the body mass index” which is determined by height and weight measurements. The machines, he adds, are good for home monitoring, but only if the user gets a more accurate reading from a physician or health professional first.

Price: $160. www.tanita.com; Brookstone, Bed Bath & Beyond and Target stores.