With John's recent frustrations over his body fat measurements, we decided to find out exactly how body fat calculators, monitors, analyzers, and scales work (lots of universal names, but one universal way of estimating your body fat percentage).
Holy Bioelectrical Impedance Analysis, Batman! Body fat scales use BIA to estimate your body composition (ratio of fat to muscle). When you step on the scale, it sends a 500 microampere current up your leg. Do not worry, humans can not even sense any current less than 1000 microamperes, much less be harmed by one.
The current travels through your body, navigating through your muscle and fat tissue. Muscle provides an easier path for the current, because it's made up of 73% water, which, of course, is a great conductor. Fat, on the other hand, offers more resistance and slows the current down. So, obviously, the less fat and more muscle you have, the faster the current will travel.
Once the current completes its path, the scale calculates the time it took to do so. It uses this information, along with your height and weight, to give you a rough estimate of your body fat percentage.
So remember, no matter what it says on the box or in the ad, no body fat scale is going to give you exact results every time. A number of factors ranging from what time of day you measure to what and when you last ate to the current room temperature can all affect the results. So, remember to use the body fat scale as a general guide to which direction your moving in, and not an absolute calculation of your exact body fat percentage.
Even with their less than perfect results, they are a great way to get a general idea of your body composition, instead of just your body weight. They are convenient, fairly accurate, and reliably inexpensive. For these reasons, they greatly outweigh (pun intended) traditional scales, because you can keep track of your changing body more accurately.
For example, if you are overweight and begin an intensive exercise routine to get in shape, you could be losing FAT while gaining MUSCLE at the same time. This is excellent and will improve your health and your physical appearance. However, if you were just using a normal scale, you would see that your weight is staying the same or maybe even increasing. This could leave you frustrated and make you give up on the excellent results you were actually achieving. If you were using a body fat scale, you could have seen that your body composition was changing for the better, and you were actually making great progress!
As with any product these days, there are literally hundreds, if not thousands, of body fat scales available. They can range in price from $ 20 to hundreds of dollars. Try to stick with one at at least the $ 50 range, and you should be alright, but if you can afford a more expensive one, you may get slightly better results. The general consensus looks to be that Tanita makes some of the most accurate models, but do a quick search on Google and / or Amazon, and you will find a wide array to choose from.