How fat is fat?

The perception
of one’s body can change when a more accurate equation is used to determine fat percentages
Thursday, October 16, 2003 | 12:00 a.m. CDT; updated 4:25 a.m. CDT, Tuesday, July 22, 2008


The subject of a photo on Page 6A of Thursday’s Missourian was misidentified. The photo was of Casey Camp, a clinical instructor in the MU Radiography Program. For an additional correction and clarification, please see page 2A.

A few weeks ago, I was dumbfounded to learn that my left arm is the fattest part of my body.

I discovered this after having a body composition assessment that used a “dual energy x-ray absorptiometry” procedure, or DXA, to look at the percentage of fat versus muscle or lean tissue in the body.

The DXA, a technique originally used to measure bone density, scanned my entire body with a dual x-ray beam while I lay on a padded table wearing a blue and white hospital gown. The procedure lasted less than 10 minutes, and radiologic technologists immediately analyzed the results.

Here they are:

  • Left Arm: 40.7 percent
  • Right Arm: 35.8 percent
  • Trunk: 24 percent
  • Left Leg: 35.7 percent
  • Right Leg: 33.3 percent
  • Head (head fat — who knew?): 18.5 percent
  • Total: 28.7 percent

I wanted to measure my body fat percentage after reading about MU researcher Stephen Ball's revisions to a 20-year-old equation for measuring body fat. Ball’s new equation for measuring body fat was developed using DXA technology. Ball compared results of skin-fold equations with results from DXA technology.

Ball took results from traditional skin-fold tests — a widely used method in the field — and those using the DXA technology, then he computed them using a traditional equation, the Jackson and Pollock equation. He then compared the results and created a new equation to minimize the difference in results between DXA and skin-fold, more accurately measuring body fat.

Ball’s research, which will be published in an upcoming issue of “Research Quarterly for Exercise and Sport,” shows that the field method underestimates body fat measurements by 3 to 5 percent in women and by about 3 percent in men. His results imply that the cutoff standards for being overweight and obese need to be raised.

“If we measure them with the old skin-fold equations and they had 28 percent body fat, they wouldn’t be above that cutoff. But if we put them on the DXA machine, they’d be 32 percent,” said Ball, an assistant professor of nutritional sciences. “The old standards didn’t come from DXA, so if we are using this new equation, everybody’s going to be a little fatter. It’s not that they gained percent fat, it’s just that we think the standards need to be raised a little bit.”

To test Ball’s research, I decided to have both a DXA procedure and a skin-fold test done, but it didn’t go quite how Ball had predicted.

Ginger Dial, a personal trainer at Gold’s Gym, performed a skin-fold test using four places on the body: two on the arm, one on the back and one on the stomach. The test used Skyndex, a gun-like machine with a claw apparatus on the end to pull fat away from muscle and tissue.

I was surprised when Dial told me that I had about 30 percent body fat. According to Ball’s research, the skin fold test’s results should have been 3 to 5 percent lower than those from the DXA procedure. Instead, the skin fold test results came back 1.3 percent higher.

“Skin folds are very subjective,” Ball said when I asked him about the discrepancy. “It takes a lot of practice to get good at them, and it also depends on which sites and equations were used.”

He gave several possibilities why the skin fold test didn’t match his research, including incorrectly calibrated calipers or that Dial used a different equation than the one used in his research, which she did. Ball used the “Jackson and Pollock equations” recommended by the American College of Sports Medicine, while Dial used the Durnin formula, the preprogrammed formula used by the Skyndex gun.

Ball said that in comparing skin fold equations to DXA, he only examined one field method, but that there are many field methods other than skin folds and a multitude of equations to pick from.

I then had Ball perform a traditional seven-site skin fold test — on the thigh, chest, tricep, abdomen, above the hip, under the armpit and below the shoulder blade — using the Jackson and Pollock equations. This time, Ball’s results showed that I had 26 percent body fat, which is about a 2.7 percent difference from the DXA scan.

Both Ball and Dial said that knowing your body fat percentage is important, in part because it allows you to gauge how healthy you are. It is important to accurately access body fat because high amounts of body fat are related to diseases such as diabetes and heart disease, Ball said.

“It helps you know how healthy your client is,” Dial said. “It’s just another way to gauge your health besides the number you see on the scale.”

But Dial said she encourages people to not get too obsessed about their body fat percentages. Some people think having a very low amount of body fat makes you healthy, and that’s not true, she said.

Another way knowing your body fat percentage can help is that it can be used to help trainers develop the most effective weight loss and muscle building programs, said Mary Sebacher, clinical assistant professor in the radiography program at MU.

Although DXA scans are more accurate than the current field methods, they are not practical for everyday use. Ball said DXA machines are expensive and that is why accurate skin fold equations are important. He said accurate skin fold equations allow everyday practitioners to feel fairly certain that they are getting a reasonable estimation of body fatness.

Last winter, MU was able to purchase a DXA machine with federal grant money, said Jack Stiefvater, director of outreach and distance education for the department of cardiopulmonary and diagnostic sciences at MU. Stiefvater said one DXA instrument costs around $65,000 to $70,000.

For $50 per scan, anyone can schedule a time to have his or her body composition assessed. The DXA procedure can be performed on campus at Lewis Hall in the Missouri Mobile Health Coach, a 30-foot mobile coach where the DXA is stored, Stiefvater said. The Missouri Mobile Health Coach has traveled to central and northeast Missouri to perform body composition and bone density tests at hospitals that do not have DXA technology available.

Typically, a person does not need a doctor’s recommendation or prescription to have a DXA scan done, but most health insurance companies will not reimburse a person for a DXA scan, Stiefvater said.

To schedule the procedure, call Marilee Spencer at 884-8986.

Like what you see here? Become a member.

Show Me the Errors (What's this?)

Report corrections or additions here. Leave comments below here.

You must be logged in to participate in the Show Me the Errors contest.


Leave a comment

Speak up and join the conversation! Make sure to follow the guidelines outlined below and register with our site. You must be logged in to comment. (Our full comment policy is here.)

  • Don't use obscene, profane or vulgar language.
  • Don't use language that makes personal attacks on fellow commenters or discriminates based on race, religion, gender or ethnicity.
  • Use your real first and last name when registering on the website. It will be published with every comment. (Read why we ask for that here.)
  • Don’t solicit or promote businesses.

We are not able to monitor every comment that comes through. If you see something objectionable, please click the "Report comment" link.

You must be logged in to comment.

Forget your password?

Don't have an account? Register here.