Body-Fat Scales

Experts say body-fat scales aren't very accurate

Body-fat monitors/scales send small, harmless electrical pulses through a user's body to gauge their body weight/density. Many body-fat scales display both body-fat percentage and body-mass index (BMI). BMI is a rough estimate of body composition that is calculated using a person's height and weight. According to the Centers for Disease Control and Prevention (CDC), BMI can be useful for determining whether a person is overweight, but it's not a fool-proof method. For example, athletes with a great deal of muscle may have a high BMI reading even though they don't possess a lot of body fat. Similarly, body-fat percentages look at how much of a person's body is composed of fat. While both of these calculations can be useful, experts caution that they do not provide a complete picture of an individual's health. Experts say an individual's waist circumference, hip-to-waist ratio, blood pressure and cholesterol levels are also important indicators of health.

ConsumerReports.org opted not to test body-fat scales after a 2003 test in which all six models produced inaccurate readings. Other experts concur that body-fat scales tend to be off by as much as 5 to 10 percent. Muscle & Fitness Hers magazine consults Dr. Richard Pierson Jr., a professor of clinical medicine at St. Luke's-Roosevelt Hospital of Columbia University, on a number of body-fat measurement methods. He acknowledges that individual readings may not be accurate, but points out that body-fat scales are a good way to monitor changes in body fat over short periods of time.

Scale readings can be thrown off by a number of factors, such as how much water you drink, whether you have a full bladder or whether you have foot calluses. Cedric Bryant, chief exercise physiologist for the American Council on Exercise, tells WebMD that body-fat scales should be used under similar conditions each time, such as time of day and fluid and food intake, noting that even a woman's menstrual cycle can affect readings. "However, with all this factored in, these scales are an easy, at-home way to keep track of your weight and fat-loss progress," says Bryant.

Joy Bauer, a registered dietician in New York, puts four body-fat scales to the test in a 2007 article for The New York Times. Using her husband as a test subject, Bauer compared the body-fat estimate obtained through underwater weighing (an accurate clinical method of measuring body fat) to those from four body-fat scales. Among the four scales tested, none was off by more than 4.1 percent.

We found a number of recommendations for various Omron body-fat scales and body-composition monitors. One (now discontinued) Omron scale reads 2.5 percentage points lower than the hospital reading in The New York Times' review. A similar body-fat scale, the Omron Body Fat Monitor and Scale HBF-400 (*Est. $45) performs decently in one independent test from Australia. It has a weight capacity of 330 pounds, measured in 0.2-pound increments and measures body fat in 0.1-percent increments. About 550 owners contribute to an average rating of 4 stars out of 5 on Amazon.com, although some reviews appear to be referring to an older model.

Users at Amazon.com are generally impressed with the Omron HBF-400 scale, especially considering its price. In fact, several owners compare it to similar Tanita scales, noting that it stores data for more users and is less expensive. Reviewers acknowledge that the body-fat measurement is not accurate, but it does offer consistent readings. Several owners point out that changes over time are more important than accurate readings, so they don't see this as a major concern. That said, athletes should be aware that the lack of an "athlete" setting means body fat readings will be higher than the true reading, because this scale can't account for added muscle mass. Users also point out that you'll want to read the user manual to understand how the scale works, because it can be complicated to use initially.

The Omron Full Body Sensor Body Composition Monitor and Scale HBF-510W, HBF-514C and HBF-516B differ slightly in function but have more advanced features than the Omron Body Fat Monitor and Scale HBF-400. All offer hand grips for full-body measurement. The Omron Body Composition Monitor and Scale HBF-510W (*Est. $65) is the simplest of the three, offering measurements of body-fat percentage, body-mass index, skeletal muscle, visceral fat and body weight for up to four users. The Omron Body Composition Monitor and Scale HBF-514C (*Est. $70) offers the same measurements plus resting metabolism and body age. Unlike the HBF-510W, it has a 90-day memory. Finally, the Omron Body Composition Monitor and Scale HBF-516B (*Est. $80) has a 180-day memory.

The Omron Full Body Sensor Body Composition Monitor and Scale HBF-510W earns an average rating of 4 stars out of 5 in nearly 120 reviews at Amazon.com; likewise, the Omron Full Body Composition Monitor and Scale HBF-514C earns a similar average rating in about 155 reviews. Feedback across all models is similar, with most owners saying these scales are accurate and consistent and a few detractors who say otherwise. All three have a 330-pound weight capacity, measured in 0.2-pound increments and are backed by a one-year warranty.

For serious athletes, the Tanita Ironman Body Composition Monitor BC-558 (*Est. $345) may be worth a look. Like most of the Omron scales, which rely on an electrical current that starts at the feet and runs through the lower body, the Ironman scale includes handles to analyze the upper body. The handles are retractable and are stored on the side of the scale when not in use. The Tanita Ironman Segmental Body Composition Monitor BC-558 tracks weight, body-fat percentage, body water, muscle mass, bone mass, metabolic age and other weight data. This scale may be overkill for the average user, but testers at Women's Health magazine generally like the Tanita Ironman Segmental Body Composition Monitor BC-558 and all the information it tracks, including metabolic age. "You get a snapshot of your overall health, not just your poundage," write the editors.

A handful of owners posting to Amazon.com give the Tanita Ironman Segmental Body Composition Monitor a 4.5-star rating, but most acknowledge that the scale can be overwhelming to the average user. Additionally, one reviewer says visceral fat is one of the most crucial measurements, and cheaper Tanita models offer this same function. U.S. News and World Report staff writer Sarah Baldauf compares readings from the Tanita Ironman Segmental Body Composition Monitor BC-558 with measurements from a Bod Pod (an advanced method of underwater weighing that doesn't require subjects to get wet). In this instance, the Tanita's readings differ by just one-tenth of a percent. The Tanita Ironman Segmental Body Composition Monitor BC-558 runs on four AA batteries and has a 90-day warranty.