A measure of your body fat once required meeting with a professional at a fitness center to be pinched with calipers, heading to a special clinic to be dunked in water or getting a scan for bone density. While these methods remain the most accurate, you can get an estimate of your body fat level by stepping on a scale. Understand how these digital scales work so you know how to to interpret their results and build a healthier physique.
About Body Fat
Body fat scales measure your weight and tell you how much of that weight comes from fat tissue. Too much excess fat -- more than 20 percent in a man and 30 percent in a woman -- increases your risk of developing diseases related to being overweight and obese. A lean body contains a greater ratio of muscle to fat. Muscle requires more calories for you to maintain, so it helps your metabolism run higher and makes weight management easier. Having a lower percentage of body fat also makes you appear and feel lean and fit.
A normal, healthy body fat percentage for women is between 20 and 25 percent and it's between 15 and 20 percent for men. Athletes and fitness enthusiasts may carry less fat due to active lifestyles. All people also have some essential fat -- 3 percent in a man and 13 percent in a woman -- that supports basic bodily functions and is required to survive. Women have more of this fat stored in the hips, breasts and thighs to support a baby during pregnancy and breastfeeding.
How Digital Scales Measure Weight & Body Fat
Body fat scales measure your body fat using an electrical method called bioelectrical impedance. You stand on metal plates fastened to the base of the scale -- some models feature metal hand-holds too -- and the scale sends an imperceptible electric current through one leg, over your pelvis and down the other leg. The electrical current travels faster through muscle due to its water content. The scale evaluates the resistance it encounters as it travels through your body and plugs that into a formula to determine your body fat percentage. Usually, this formula also takes into account your height, weight, age and gender, which you enter.
The scale measures your gross weight, too -- just like a regular body-weight scale. Some have features that wirelessly transmit the information to your computer or smart phone and sync up with fitness apps.
Body Fat Scale Results Vary
Body fat scales are extremely convenient, but their measure of body fat percentage is often inaccurate. Consumer Reports reported in 2016 that six models of store-bought scales overestimated fat by 21 to 34 percent in a test comparing their effectiveness to a measurement of fat determined via air displacement.
Inaccuracies in measurement occur because the scales are sensitive to multiple variables. Your hydration status affects the scales' measure because the current faces more resistance when you're underhydrated. If you exercise or eat close to the time of measurement, this can affect your hydration status and skew the results. Calloused, dirty or wet feet interfere with the contact of your body with the foot electrodes. If you have a hip or knee replacement, the body fat measurement will also be affected as the current may register an error when it comes into contact with man-made devices. The quality of the scale you use also influences accuracy.
Body Shape and Size Affects Scale Accuracy
The shape of your body could also cause misreadings with a body fat scale. Because the scale usually shoots the electrical current through your legs, it might underestimate fat in people who have thinner legs and a larger torso or overestimate fat in those with heavier hips and slight upper bodies. Body fat scales with hand and foot electrodes may be more accurate, but still have notable levels of error. According to a review published in the Journal of Diabetes Science and Technology in 2008, body fat scales are also less accurate in overweight and obese people. .
Best Body Fat Measures
Digital body fat scales may have a high degree of inaccuracy -- but at least they're consistent. This means you can use one to judge trends in your body fat -- whether you're increasing or decreasing over the course of several weeks or months. To get the most comparable results, measure yourself at the same time of day, wearing the same clothes and with the same level of hydration.
Turn to more accurate measures of body fat and fat distribution to get the best picture of the health of your body composition. Waist circumference, for example, can help you determine if you're carrying too much fat in your middle -- something a body fat scale cannot determine. A man with a waist size of 40 inches or more, or a woman with one of 35-plus inches, carries a lot of visceral, or belly, fat. This type of fat is inflammatory and releases compounds that increase your risk of developing serious diseases, including cardiovascular disease, Type 2 diabetes and some cancers.
Gold standard methods of body fat measurement directly examine the makeup of your body and include hydrostatic weighing, air displacement, Dual-Energy X-ray Absorptiometry and CT or MRI scans. The cost for these methods of measurement vary, and you'll need to visit a clinic that has the specialized equipment and trained facilitators.
- Berkeley Wellness: Body Fat Scales: Step Right Up?
- Today's Dietitian: When Thin is Fat
- Penn Rec: Body Composition Information and FAQ’s Sheet
- Consumer Reports: Body-Fat Scale Review
- Journal of Diabetes Science and Technology: Body Composition Methods: Comparisons and Interpretation
- Georgia State University: Body Fat Composition