I wasn't aware that there is a newer, supposedly more accurate technique for measuring body fat percentage. It's the DEXA scanner, which is used for measuring bone density.
I had a bone density scan today as part of an osteoporosis research study conducted by a local medical school. Along with my bone density results, they also gave me my total body fat percentage.
I didn't realize that the DEXA scanner could be used for this. I looked it up and apparently it's the new "gold standard" for body fat measurement:
www.new-fitness.com/body_fat_analyzing.html
DEXA (Dual Energy X-ray Absorptiometry) - A relatively new technology that is very accurate and precise, DEXA is based on a three-compartment model that divides the body into total body mineral, fat-free soft (lean) mass, and fat tissue mass. This technique is based on the assumption that bone mineral content is directly proportional to the amount of photon energy absorbed by the bone being studied.
DEXA uses a whole body scanner that has two low dose x-rays at different sources that read bone and soft tissue mass simultaneously. The sources are mounted beneath a table with a detector overhead. The scanner passes across a person's reclining body with data collected at 0.5 cm intervals. A scan takes between 10-20 minutes. It is safe and noninvasive with little burden to the individual, although a person must lie still throughout the procedure.
DEXA is fast becoming the new "gold standard" because it provides a higher degree of precision in only one measurement and has the ability to show exactly where fat is distributed throughout the body. It is very reliable and its results extremely repeatable; in addition, the method is safe and presents little burden to the subject. Although this method is not as accurate in measuring the extremely obese and the cost of equipment is high, DEXA is quickly moving from the laboratory setting into clinical studies.
Three years and 20 lb. ago, I underwent a DEXA scan for an article on metabolism. Even though my weight was down then, I was a little afraid I would prove to be one of those generally skinny guys with enormous guts that have been increasingly classified of late as "weight normal, metabolically obese."
Here, for your possible amusement and/or scientific interest, is my memory of the DEXA experience:
Michelle H., an attractive 26-year-old scan technician at PBRC, tells me to take off my clothes and change into a zipperless gown. I’ve just gotten sprung from the metabolic chamber, and Tuong Nguyen has arranged for me to bivouac with Michelle in the DEXA lab while he compiles my metabolic results. At Michelle’s instructions, I feel a spike arise somewhere deep in my metabolic physiology.
“I used to be almost a quarter pure lard,” I say, emerging from the changing room in the gown, which may or may not be on backwards. “You think I’m any less now?”
“Hard to tell just from looking at you,” she replies with a North Carolina drawl. “We’ll know more soon.”
As she leads me over to a digital scale, Michelle explains that DEXA (dual-energy x-ray absorptiometry) was originally pioneered to diagnose osteoporosis in women. In recent years, it’s also emerged as the single most accurate way to determine body composition, supplanting the old “gold standard”—underwater weighing—at many obesity research centers.
Researchers even have a diagnosis for when otherwise skinny guys put on too much abdominal fat: "weight normal, metabolically obese." I hadn't reached this point--yet--but I worried it could one day prove my fate.
“Okay,” Michelle says, pointing to a digital scale. “Step up.”
Red numerals on the digital scale flicker around nervously before finally settling on 75.0 kilograms.
“Now we get to subtract the gown,” she says.
A few calculations later, and I get the Americanized results: 164.4 pounds, essentially identical to my college “fighting weight.” When Michelle next measures my height with a digital measuring stick, I brace myself for the likelihood of significant shrinkage. But once again the news is good: 6’ .76”—less than a quarter inch off my lifetime record. Maybe the tag team of life and gravity haven’t beaten me down quite so much as I thought. My body mass index, or BMI, is 22.0—safely in the “not too fat, not too thin” zone.
Now, however, comes the real money shot: the DEXA scan itself. True, I’ve cut 20 pounds in the five years since the underwater weighing, but the question remains what kind of pounds have I shed? If my body has simply cannabilized its skeletal muscle for fuel, something not uncommon in cases of significant weight loss, I may have only turned myself into a skinnier, weaker, slower-metabolic version of the fat guy I used to be.
“I need you to lie down here,” Michelle says, indicating a sliding gurney beneath a movable QDR 4500 Hologic scanner arm. For the next three minutes, the arm glides back and forth, spraying my body with a piddling 5 microsieverts of radiation (the same amount we get each day just living on earth.)
Once the scan is completed, I get dressed and go to look over Hall’s shoulder. She’s using a computer mouse to draw red boxes around my arms, legs, trunk, spine, and head. A grayish halo surrounds my bones. “That’s your skeletal muscle,” she says, adding that the even finer layer on the perimeter is fat.
“Maybe my eyes are getting worse with age,” I say, “but I can’t see much fat.”
“You really don’t have much at all,” she replies, smiling. “The software will let us know exactly how much.”
The printout proves better than I could have hoped for. I’m down to 17.1 percent total body fat, which Hall says is distributed in a healthy, symmetrical way. My leanest parts are my legs—the left one at 14.2 percent fat, and the right one at 13.6. My abdomen, at 18.7 percent fat, is in no way suggestive of abdominal obesity, Hall says. To my surprise, my gut is not even my fattest body part. My head, at 20.1 percent, takes this dubious honor.
I wonder if researchers have a diagnosis for this, too: “weight normal, fat head.”
Three years and 20 lb. ago, I underwent a DEXA scan for an article on metabolism. Even though my weight was down then, I was a little afraid I would prove to be one of those generally skinny guys with enormous guts that have been increasingly classified of late as "weight normal, metabolically obese."
Here, for your possible amusement and/or scientific interest, is my memory of the DEXA experience:
Michelle H., an attractive 26-year-old scan technician at PBRC, tells me to take off my clothes and change into a zipperless gown. I’ve just gotten sprung from the metabolic chamber, and Tuong Nguyen has arranged for me to bivouac with Michelle in the DEXA lab while he compiles my metabolic results. At Michelle’s instructions, I feel a spike arise somewhere deep in my metabolic physiology.
“I used to be almost a quarter pure lard,” I say, emerging from the changing room in the gown, which may or may not be on backwards. “You think I’m any less now?”
“Hard to tell just from looking at you,” she replies with a North Carolina drawl. “We’ll know more soon.”
As she leads me over to a digital scale, Michelle explains that DEXA (dual-energy x-ray absorptiometry) was originally pioneered to diagnose osteoporosis in women. In recent years, it’s also emerged as the single most accurate way to determine body composition, supplanting the old “gold standard”—underwater weighing—at many obesity research centers.
Researchers even have a diagnosis for when otherwise skinny guys put on too much abdominal fat: "weight normal, metabolically obese." I hadn't reached this point--yet--but I worried it could one day prove my fate.
“Okay,” Michelle says, pointing to a digital scale. “Step up.”
Red numerals on the digital scale flicker around nervously before finally settling on 75.0 kilograms.
“Now we get to subtract the gown,” she says.
A few calculations later, and I get the Americanized results: 164.4 pounds, essentially identical to my college “fighting weight.” When Michelle next measures my height with a digital measuring stick, I brace myself for the likelihood of significant shrinkage. But once again the news is good: 6’ .76”—less than a quarter inch off my lifetime record. Maybe the tag team of life and gravity haven’t beaten me down quite so much as I thought. My body mass index, or BMI, is 22.0—safely in the “not too fat, not too thin” zone.
Now, however, comes the real money shot: the DEXA scan itself. True, I’ve cut 20 pounds in the five years since the underwater weighing, but the question remains what kind of pounds have I shed? If my body has simply cannabilized its skeletal muscle for fuel, something not uncommon in cases of significant weight loss, I may have only turned myself into a skinnier, weaker, slower-metabolic version of the fat guy I used to be.
“I need you to lie down here,” Michelle says, indicating a sliding gurney beneath a movable QDR 4500 Hologic scanner arm. For the next three minutes, the arm glides back and forth, spraying my body with a piddling 5 microsieverts of radiation (the same amount we get each day just living on earth.)
Once the scan is completed, I get dressed and go to look over Hall’s shoulder. She’s using a computer mouse to draw red boxes around my arms, legs, trunk, spine, and head. A grayish halo surrounds my bones. “That’s your skeletal muscle,” she says, adding that the even finer layer on the perimeter is fat.
“Maybe my eyes are getting worse with age,” I say, “but I can’t see much fat.”
“You really don’t have much at all,” she replies, smiling. “The software will let us know exactly how much.”
The printout proves better than I could have hoped for. I’m down to 17.1 percent total body fat, which Hall says is distributed in a healthy, symmetrical way. My leanest parts are my legs—the left one at 14.2 percent fat, and the right one at 13.6. My abdomen, at 18.7 percent fat, is in no way suggestive of abdominal obesity, Hall says. To my surprise, my gut is not even my fattest body part. My head, at 20.1 percent, takes this dubious honor.
I wonder if researchers have a diagnosis for this, too: “weight normal, fat head.”
