Starting out in GQ because I believe there is a factual answer.
What is the best way to measure body fat %, when given the three most popular choices?:
calipers
buoyoncy tanks
electrical impedence
As common as bathroom scales are now, they may very well be replaced by a combo scale and body fat analyzer. Most department stores that sell scales are now selling devices that you step on barefooted. The scale calcs your weight and uses electrical impedence to measure body fat. You then get your weight total, your body fat total and fat as a %, among other things.
These new scales keep records to track changes.
Are these things accurate? Could they be sold if they weren’t?
Is electrical impedence better than the caliper/pinching technique and/or the buoyancy tanks?
What is the science behind electrical impedence to measure body fat? What could throw off the accuracy?
Considering the convenience, if these things are accurate, I’m getting one soon. I don’t have the time/money to pay professionals for buoyancy or caliper tests.
let me start by saying i am not familiar with the actual equipment, only somewhat familiar wit hthe processes behind it:
electrical impedance body fat analysis measures the body’s electrical impedance and plugs this into a formula involving height, weight etc to estimate body fat %. Each company will have it’s own formula and probably its own results. The overall impedance is heavily weighted towards the limbs (higher impedance) so this must be accounted for in the final calculations. Other factors such a body hydration, etc also come into play. Muscle > Fat > Bone when it comes to electrical conductance.
various current frequencies can be used (typically 50KHz, 1 mA) to penetrate different tissues. ~50kHz is typically used because it will “penetrate” the skin. the skin has many reactive components that are time and mood affected(major source of error).
if you end up getting one of these, make sure you have the same stance each time you measure. wear pants as your thighs can short out the path and affect measurements.
it depends on your application, but i would just buy a caliper and use that. Body fat has less to do with overall health than many other elements you could be monitoring and you don’t need a fancy piece of equipment to tell you how much impedance is beween your two feet…
One of the major drawbacks to calipers that I most familiar with is the consistency needed in taking the measurements. In order to get comparable readings you have to take the measurements at the same point on the body everytime. The last time I had my body fat done this way it took the person a few tries to get it right. That leads me to believe that there’s more room for error.
One method you didn’t mention is the “bod pod.” It measure the bodies displacement in an air filled chamber. My gym has one and I’ve had my body fat analysis done there a few times. I believe “bod pod” also had a web site devoted to explaining the whole process.
When I was in college, my phys ed professor told us that the water-tank measurement is the most accurate. The caliper test uses measurements which extrapolate to measurements made with water-tank tests, IIRC. I do not know if the electrical impedence test was available back then (ca. 1986).
Best method is the tank. Others have too many variables.
But the impedence method is good for watching changes. I have a scale with an impedence thingy built in and it’s useful for watching whether it goes up or down. You have to be consistent in how you use it (same time of day, naked, etc.).
I participated in a lab demonstration of exactly this issue some years ago. We tested body composition using each of the methods listed above and graphed the results. The range was astounding.
Hydrostatic weighing is by far the most accurate (something on the order of +/- 3% I believe). But it’s a lenghty procedure that involves specialilzed equipment.
The point of the demonstration I participated in was to be cautious in reporting estimates of peoples’ body fat. However, for an INDIVIDUAL who understands that the other methods carry some large-ish margins of error, they might be acceptable.
As I recall, caliper measurements was the least accurate. However, it should be noted that their accuracy goes up significantly as more skin sites are utilized, and by the expertise of the person administering the test.
I have one o’ those scales. Like CookingWithGas says, it’s most useful for tracking over time. I did some research before I bought it, and basically, there’s no real “accurate” method for gauging body fat other than autopsy. Given that most of us don’t want to go through an autopsy simply to find out our body fat, electrical impedence is as good a measure as any.
This isn’t something that you would be able to do yourself, but AFAIK the most accurate way is dual absorbance X-ray.
I once participated in an USDA diet study that measured food intake correlated with body fat. I don’t know a lot about the specifics, but apparently fat and muscle absorb X-rays differently. Since most people exaggerate their height and understate their weight, the researchers insisted on measuring the subjects themselves. I also had to get the X-ray scan, which entailed laying flat on my back while the scanner passed over me. It generated a full body X-ray of my skeleton and supposedly my body fat compared to muscle mass information.
I measured out at 17% body fat, which is in the normal healthy range. I have veins visible on my arms and legs and probably would be considered lean/ or at least not fat. I?m always amused by the guys at the gym who claim they are something like less than 5% body fat when they?re not really leaner than me. Just like height and weight, people seem to estimate their body fat in the most favorable light?whether they really know it or not.
As far as the other methods of measuring body fat, the researchers seemed skeptical and told us X-ray was the most accurate and that?s why they used it. And since they had the equipment, they used it instead of calipers or water tanks?which they claimed were too inaccurate and unreliable for the study.