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Body Fat Testing

Evaluating the Options

Body fat testing has complex meaning in sports medicine. A physician might measure body fat in an obese man as a baseline for measuring progress on a weight loss program. Yet the next patient could be a competitive athlete who asks for body fat testing to guide her performance-enhancement efforts.

Adding to the complexity are the wide choices that clinicians have for assessing body fat—from measuring tape to high-tech devices. Also, some clinicians warn about overtesting.

Testing Devices and Techniques

Underwater weighing and dual- energy x-ray absorptiometry (DEXA) are the only body fat testing methods that have been scientifically validated and, thus, are considered the "gold standards." Similar results are obtained with Bod Pod (Life Measurement Instruments, Concord, California) chambers, often found in exercise physiology labs. (Body fat is calculated based on air, rather than water, displacement.)

Because underwater weighing and DEXA are time-consuming and expensive, less costly and more convenient options are generally used in clinical practice.

Waist-to-hip ratio. This ratio is a general measure of fat distribution. The waist is measured at its narrowest point, then the hips are measured at the widest point. Then the waist measurement is divided by the hip measurement. Some experts note that the most commonly used table for interpreting ratio results is based on an athlete's body type and may not be applicable to all patients.

Skinfold testing. Measurements are taken with an inexpensive caliper (figure 1A: not shown) at one or several body sites. Results come close to underwater weighing and DEXA, but the technique requires much practice to obtain accurate results. Several equations can be used for skinfold testing.

Bioelectrical impedance analysis. An easy-to-use device (figure 1B: not shown) quickly measures the body's resistance to a low-level electrical charge. Resistance level relates to body water content, an indirect assessment of total body fat. A patient's hydration status, however, can alter the results. No national standard for the devices has been developed; total body fat calculation is based on each company's proprietary formula.

Near-infrared interactance. With this tool, a fiber-optic probe, typically placed on the center of the biceps of the dominant arm, measures tissue composition. Near-infrared devices (figure 1C: not shown) are portable and quick to use, but no national standards exist for them. They are the newest body composition devices on the market.

What's Happening in the Field?

Responses from an informal survey posted on the American Medical Society for Sports Medicine Internet mailing list reflect many different perspectives on and experiences with body fat testing.

Many physicians, such as Joe Himes, MD, a family physician in Shell Knob, Missouri, prefer the speed and convenience of assessing patients' weight status with body mass index (BMI) tables. "These are about as accurate as inexperienced caliper use and are much quicker and accessible," he says. Ironically, he notes, more precise body fat measurement might be more useful for underweight patients. Body fat testing would provide an objective measure for identifying, classifying, and monitoring eating disorders.

Other physicians, such as William O. Roberts, MD, a family physician in White Bear Lake, Minnesota, and an editorial board member of The Physician and Sportsmedicine, have become skilled at assessing body fat with calipers. "I use the Lohman equation for certifying wrestlers and an alternate equation on occasion for patients who request analysis," he says. "Mostly, I use the belly pinch and compare it to the forearm as a quick measurement of where male patients should be."

Others are embracing electronic devices that estimate body fat percentage. Phillip Zinni III, DO, ATC, medical director of corporate health services at E. & J. Gallo Winery in Modesto, California, has used near-infrared devices for about 10 years in private practice and in his current position. He's used the device to monitor patient progress on weight loss programs and to assess patients' health risks in wellness programs.

Clinicians who work with sports teams tailor body fat testing to their needs. Nick Bent, PT, who has worked with two English football clubs near Birmingham, England, says skinfold measurements are routinely taken as part of the general musculoskeletal assessment. In another context, a nutritionist who worked with one of the teams incorporated bioelectrical impedance measurement in dietary assessment and recommendations. "The players were obsessed with low body fat, whereas I wished they were more obsessed with their glycogen stores," Bent says.

Body fat testing for women sports teams is controversial. Assessing body fat percentage can help identify patients who are at risk for eating disorders; however, others believe that focusing on a body fat number may initiate an eating disorder. The women's issues committee of the Canadian Academy of Sport Medicine (CASM) has submitted a working paper to the CASM that supports abandoning body composition testing for female athletes and dancers.

Experts Weigh In

Experts in the clinical applications of body fat testing say before assessing patients' body fat, physicians should first evaluate how important it is to know the result.

Work-up and therapy decisions for chronic diseases such as hyperlipidemia or dysmetabolic syndrome (formerly known as syndrome X) represent crucial body fat assessment, says Ralph La Forge, MS, an exercise physiologist who is managing director of the Duke Lipid Clinic and the Disease Management Preceptorship Program at the Duke University Medical Center in Durham, North Carolina. Chronic disease risk, particularly diabetes, cardiovascular disease, and hypertension, has been shown to be associated with visceral fat in the abdominal region, particularly atherogenic abdominal fat.

La Forge says waist circumference measurement is used for patients with diabetes and hyperlipidemia. The physician places a measuring tape at the bottom of the patient's iliac crest. The tape is pulled taut as the patient exhales. He notes that other body fat measurement devices and techniques are useful for screening but should not be used to make treatment decisions.

On the other hand, Richard Cotton, MA, an exercise physiologist and consultant with First Fitness, Inc, based in Salt Lake City, cautions against focusing too much on body fat measurements. "Patients become discouraged if the number doesn't change," he says.

Each of the body fat testing methods has its strengths and weaknesses, he notes. For example, though skinfold measurements, when performed correctly, correlate closely with underwater weighing and DEXA, Cotton notes that "grabbing a chunk of hip on a patient who is already weight-obsessed is not a good thing." And though BMI is a good general indicator of body fat, it is insensitive to the quality of weight, he says. In general, a BMI of greater than 27 in people age 35 or older is considered obese, "but Michael Jordan and Mark McGwire have had BMIs of 30."

Cotton has had success monitoring patients' body fat changes by simply asking patients to monitor how a certain pair of pants feel. He has several tips for physicians who want to incorporate body fat testing into their diet and activity assessments:

  • Select, learn, and stick with the same body fat testing technique so that monitoring of results is uniform.
  • Compare your skinfold testing skills against a reliable source such as underwater weighing, DEXA, or someone who is skilled at taking skinfold measurements.
  • Consider delegating body fat measurement to a specially trained staff member.
  • Focus on the patient's activity and diet habits, rather than the body fat percentage.

Lisa Schnirring

Field Notes

Tattoos Predict Hepatitis C Risk
Tattooing appears to be a major route of hepatitis C infection and is perhaps the biggest contributor to the spread of the disease—even bigger than injection-drug use, according to a study in the March issue of Medicine.

Researchers from the University of Texas Southwestern Medical School in Dallas surveyed and tested 626 patients who sought treatment at an orthopedic spinal clinic. Patients were surveyed and tested in 1991 and 1992, before widespread hepatitis C testing began. Of the 113 patients who had a tattoo, 25 (22%) were infected with hepatitis C. (Of the 513 patients who did not have tattoos, 18 [3.5%] were infected.) Few of the tattoo-associated infections could be traced to injection-drug use, transfusions, or other known exposure sources.

The authors found that the hepatitis C risk was increased in people who had several tattoos or had ones that were large and complex. Tattoos acquired in commercial tattoo parlors were also associated with a higher risk of infection. Hepatitis C and other infectious diseases can be spread by reuse of needles or dye and by inadequate sterilization technique. The authors write that few states have laws addressing safe tattooing practices, and even fewer monitor and enforce the standards.

Nearly 4 million Americans have chronic hepatitis C infection, and an estimated 10,000 deaths occur each year from hepatitis-C related cirrhosis and liver cancer.

Exercise's Mood Benefits: Move It or Lose It
University of California, San Diego researchers have found that the mood benefits of exercise erode when patients become inactive, according to a study in the March 15 issue of the American Journal of Epidemiology.

The researchers followed 944 residents of Rancho Bernardo, California, from 1984 to 1987 and from 1992 to 1995. During the 1980s, the residents (nondepressed as measured by the Beck Depression Inventory, ages 50 to 89) exercised at least three times a week. Upon follow-up in the 1990s, researchers found that the residents who continued to exercise had lower depression inventory scores. Those who stopped exercise had depression inventory scores that were similar to subjects who had never exercised.

The good news is that the researchers found that increased age was not a factor. When analyzing a group who began exercising in the 1990s, researchers found mood benefits similar to subjects who had exercised continuously over both decades.