Are Body Fat Scales Accurate?

I went shopping for a regular body weight scale the other day and was overwhelmed with options. It seemed most brands have added all kinds of features, including body fat measurements, but how accurate are they?

November 3, 2015
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I went shopping for a regular body weight scale the other day and was overwhelmed with options. It seemed most brands have added all kinds of features, including body fat measurements, but how accurate are they?

As a gym owner and personal trainer, tracking body composition is an extremely important aspect of fitness. That is why we purchased a state-of-the-art piece of equipment, the InBody, for our gym to track things like body fat and muscle mass for our clients.

Of course I have to raise an eyebrow when there is a $39.99 scale boasting it has some of the same features our high-dollar machine does. It took me years to pay for that machine!

While I had a good idea how these scales worked and what to expect, I decided to dive into the science behind body fat tracking devices to see if they really could track body fat accurately or if they were a big fat waste of money.

How It Works

Most of the scales and handheld devices on the market use the biolectrical impedance analysis (BIA) method to track body fat. BIA runs a light electrical current through your body, measuring the amount of mass impeding the current. Fat-free mass contains mostly water but fat contains very little water. As you know, water is a good conductor for electrical current. However, fat mass is not. The machine uses the data it receives from the impedance measurements to calculate body fat percentage.

Pros And Cons

The obvious pro of the new scales on the market is they are an affordable way to track changes in body fat. They are also easy to use. The problem with using these devices is the electrical current doesn’t go through the entire body, so it doesn’t measure the entire body.

Most of the units on the market only measure part of the body. For instance, the foot scales are only sending the current through one leg and out the other. Handheld devices send the current through one arm and out the other. Both miss the rest of the body entirely.

Also, an electrical current will only follow the path of least resistance. This means some of the tissue may be missed completely. So, not only are these machines not measuring the entire body, they aren’t even measuring all of the tissue in the part of the body the current is traveling though.

I was relieved to learn why our machine is so much more accurate. Not only does our machine have eight points of contact, connecting both hands and feet, it also uses multiple currents. Most scales only use one single frequency at 50kHz, while our professional body composition machine uses multiple broadband frequencies from 1kHz to 1,000kHz.

While I doubt you will go out and spend several thousand dollars on a professional unit to get accurate measurements, it is good to know the difference between a professional machine, like the InBody, and a retail device that advertises similar measurements.

Though the body fat scales on the market today are not very accurate, their measurements can still help track changes to some degree. For instance, if your first measurement says you are at 25% body fat and your second measurement says you are at 23% body fat, you know you are losing fat even if those percentages are not completely accurate.

It’s like weighing on an unbalanced scale. Even if your scale is not accurate, as long as it does not fluctuate, you can still track weight loss or weight gain pretty accurately.

Finally, in addition to these scale’s shortcomings, you yourself can throw the machine off even more by what you do or do not do prior to the reading. Hydration plays a big role in getting an accurate reading, even in high-dollar machines.

Remember, these scales are reporting body fat percentages. This means if you increase the percentage of fat-free mass, you are decreasing the percentage of fat mass. Even if you truly gain one pound of muscle, your body fat percentage can go down even if you haven’t lost one ounce of fat.

With that said, this is why eating and exercising before you weigh in matters. Body fat measurements can be lower if you measure yourself after a meal, which the machine may read as fat-free mass.

Exercise prior to your reading affects accuracy due to freshly trained, “pumped up” muscles. The temporary increase in muscle tissue throws the percentages off in the same way. Therefore, it is recommended you do not exercise, eat, or drink prior to measuring. You should also always measure your body fat at the same day and time each weigh in.

Fit Or Flop?

So, is it really worth it to upgrade your scale to one of these fancy high-tech scales? I say “no.” These body fat reading devices are a big fat flop. I would only consider purchasing one of these scales as a last resort.

You can get a more accurate reading at a local gym or doctor’s office. I spend your hard-earned money on accurate information instead. Most trainers offer body fat measurements with a skin calipers if they don’t have a professional body composition machine. One measurement per month is plenty to track changes in body composition to help you can reach your goals.

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