DEXA Body Composition

Why should I get a total body composition test using DEXA?

 

There are many reasons why someone should have a total body composition test. DEXA scans can be a powerful motivational tool for people tracking weight loss, nutrition, exercise, rehabilitation, and overall health. Think of every time you’ve used a scale to track your progress – while this number is a good way to track progress, it doesn’t tell you what type of weight your losing or gaining. Is it fat? Muscle? Both? With DEXA, you will definitively know what changes your body has made.

 

People who should consider having a DEXA scan fall into 4 categories:

 

1. If you are trying to lose weight & want to monitor body fat loss and muscle growth from exercise, DEXA is an accurate measure of weight management and fitness programs.

2. If you are proactive in your health and want to reduce the risks of heart disease, diabetes, high blood pressure, high cholesterol, cancer and obesity – a DEXA scan is a positive first step.

3. If you are an athlete or bodybuilder and you’re trying to achieve a low ratio of fat to lean tissue mass, you can use DEXA to track muscle atrophy from injury, as well as muscle gain during rehabilitation.

4. If you are interested in weight training and you want to monitor muscle mass, and want to get a fat scan and analysis for your health, DEXA scanning provides insight into your body’s measurements.

 

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What’s involved in a DEXA evaluation?

 

The x-ray technician will help you lie on your back on a padded table. An x-ray generator is located below this table, with the imaging device attached to it. The scanner, which is positioned above you, will move back and forth as it measures your bone density or body composition. The machine is very open and does not feel “closed in.”

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You will be asked to hold still and may be asked to keep from breathing for a few seconds while the x-ray picture is taken to reduce the possibility of a blurred image. 

 

The DEXA machine sends a thin, invisible beam of low-dose x-rays consisting of two different beams. The lower intensity beam is only absorbed by soft tissue (muscle and fat), whereas the higher intensity beam gets absorbed both by bones and by soft tissue. These differences in absorption are used to determine bone mineral density (BMD) and body composition values. These measurements are taken with only one pass of the scanner, and the results are immediate.

 

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What about other, cheaper options?

 

Essentially, you get the accuracy you pay for. Other popular methods like hydrostatic weighing, the Bod Pod, and calipers rely on calculated measurements of body fat that are influenced by uncontrollable environmental variables and accidental, or intentional, human error. 

 

Underwater weighing, the pre-DEXA body composition gold standard, assumes that densities of fat mass and fat-free mass are constant. However, this doesn’t take into account a few important and potentially conflicting variables that strongly influence the equations used to calculate body density. For example, athletes typically have denser bones and muscles than non-athletes. Thus, their measurements often underestimate body fat percentage. Conversely, the body fat of elderly patients, especially those with osteoporosis, may be overestimated due to these body density assumptions.

 

Other popular calculated measurements have similar limitations. Subjective variables are inherent to any calculated measurement of body fat. Therefore, any discrepancy between DEXA and another method is not due to an overestimate of the DEXA, but rather inconsistencies inherent in other measurement methods. Of these, measurements by caliper (skin fold) and electrical impedance testing have proven to be the most wildly inaccurate. In fact, measurement by caliper significantly underestimated body fat percentage by 3.2–5.6% in women when compared to the DEXA.

 

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How should I prepare for the scan?

 

On the day of the exam you may eat normally. You should not take calcium supplements for at least 24 hours before your exam. You should wear loose, comfortable clothing, avoiding garments that have zippers, belts or buttons made of metal. Objects such as keys or wallets that would be in the area being scanned should be removed. You may be asked to remove some or all of your clothes and to wear a gown during the exam. You may also be asked to remove jewelry, removable dental appliances, eye glasses and any metal objects or clothing that might interfere with the x-ray images.

 

Inform your physician if you recently had a barium examination or have been injected with a contrast material for a computed tomography (CT) scan or radioisotope scan. You may have to wait 10 to 14 days before undergoing a DEXA test.

 

Women should always inform their physician and x-ray technologist if there is any possibility that they are pregnant. Many imaging tests are not performed during pregnancy so as not to expose the fetus to radiation. If an x-ray is necessary, precautions will be taken to minimize radiation exposure to the baby.

 

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Still think BMI measurements are good enough?

 

Don’t take it as gospel the next time you read that Suzie Fitness Model maintains a 6% body fat level – body composition measurements have been proven to be grossly underestimated. In a recent Texas A&M study, the body composition and bone mineral density of elite female college athletes were observed and tracked over competitive seasons. Although not the intent of the study, an interesting juxtaposition emerged between popularly reported body fat percentages, and those measured in elite athletes. For example, the DEXA-measured average body fat percentage of female swimmers was measured at 22.2%, and 15% for track sprint athletes. These numbers differ vastly to what we would assume they would have, due in part to the popular notions of single-digit leanness.

 

While body mass index (BMI) can be helpful to track your progress, body fat percentage is superior as a measure of healthy weight. Over the long haul, weight means nothing unless you can accurately assess whether that weight you’re trying valiantly to lose or gain actually consists of fat or muscle. Think your diet and training regimen is really working? The DEXA is a simple and sure-fire way of letting you know.