Understanding Body Composition and Testing for It

  • 3 Minutes Read

Curious about what your body weight really means? There are options to test your body composition, but why would you, what are the pros and cons, and are they reliable?

Understanding Body Composition and Testing for It

Let’s face it, the most common tool used for collecting data on our changing bodies is the scale. While how loose our favorite jeans are fitting is what we talk about, it’s the numbers that flash in front of us when we step onto the small platform in our bathroom that stick with us. But sometimes we want more information. Perhaps you have heard the term, “body composition,” and we’ve covered it before, in part. But let’s look at it in more detail.

First, let us remind you that Body Fat is not BMI. BMI (Body Mass Index) is a good indicator of body fat, but it is not an actual measurement of body fat percentage. That’s what body composition is.

While there are a few methods of determining body fat composition, we’ll focus on the two most accurate/accessible: the “pinch test” and hydrostatic weighing. Others, like the Omron Body Fat monitor, are not recommended due to their erratic measurements.

In January, I did a little comparative test and had my body composition tested two ways, back to back. I went to my local university and for $25 I had a hydrostatic weigh test. Immediately after I went to my personal trainer and had him do a seven-point pinch test. As instructed for the hydrostatic test, I had fasted for at least 12 hours.

The difference was notable. The hydrostatic weigh results showed a body fat percentage 6% more than the pinch test, and at my weight that translates to a difference of about 15 pounds of fat! If I wanted to lose that at a modest rate of 1.5 pounds per week, that’s an extra 10 weeks of dieting and calorie tracking.

So what number do I go with?

After researching a bit more and talking with my trainer, I found out that the hydrostatic test has a 2-3% margin of error (American College of Sports Medicine), and the pinch test comes with a 6% margin of error. Therefore I could deduce that the hydrostatic result fell within the margin of error of the pinch test but the pinch test did not fall into the margin of the hydrostatic test. By those facts it seemed appropriate to split the difference, add 3% to the pinch test and deduct 3% from the hydrostatic test, which falls into each one’s margin of error.

But what contributes to margin of error? Going through the hydrostatic weigh test I learned that it’s all about water displacement inside a controlled tank (see pic above). The test itself consisted of three individual tests and averaging out the results, unless there was a notable outlier, which would be removed from the average.

The test is this: Enter the tank, submerge yourself so the volume of water in the tank can calibrate. Sit on a platform and expelling all your breath submerge, crunch down, and grab onto two handles at the bottom of the pool. You hold this position until all visible air bubbles are gone + three seconds. It’s this “+ three seconds” that’s the hardest. You have no air in your body and it seems like forever before the assistant bangs on the tank signalling you can come up. But if there’s any temptation to keep a half-breath of air in your lungs, know this, air = fat in this test.

Since the test is about water displacement, any pocket of air, inside your body or outside, gets translated as fat in the system. This goes for air in your digestive tract or a bubble in your shorts pocket.

With the pinch test, the margin of error is greater because there are more complications to alter the results, ranging from water retention, time of month for women, and if you’ve recently lost a lot of weight and have loose, extra skin. Another important factor is the skill of the tester. If possible, find a certified trainer who has experience and a high quality tool.

What I valued from the pinch test that the hydrostatic test could not provide is that I had measurements for seven different points on my body. Not only did I have my overall body fat percentage, but I knew that my belly had a higher percentage of fat than my thighs. As I’m lifting weights and changing my muscle tone, I can now track changes for specific parts of my body. With the hydrostatic test, I have one number that represents my body as a whole. For me, that’s not as useful.

With my comparison, I have essentially calibrated my personal trainer’s test against the gold standard of the hydrostatic weigh test. As part of my training regimen this year, I’ll have monthly body composition tests to track changes and I’ll be confident in the results. While I won’t get a hydrostatic test every month, I’ll know to add percentage points to the pinch test results.

Knowing my percentage of body fat and muscle mass helped me redefine my personal weight loss goals. I can place my weekly weigh-ins in a bigger context and know I’m striving to reach a 15% body fat percentage. I’m less discouraged by weight fluctuations because I know I’m trying for gains in mass and reductions in fat.

Since using MyNetDiary is about tracking and understanding data, a body composition test is one piece of the overall puzzle that may help you with your health goals. Have you had one?

Need more reason to consider knowing your body composition? Adrienne Osuna shows what a two pound “weight loss” can really look like. I like her term “body recomposition.”

Weight Loss->Body composition
Feb 24, 2017
Ryan Newhouse - health writer, MyNetDiary

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