I was asked a question yesterday that everyone needs to hear the answer to.
How accurate is my body fat scale?
The answer is that it is not very accurate and it is very accurate.
Here is the deal: for actually telling you how much body fat you have they are woefully inaccurate.
For telling you if you are gaining or losing body fat they are quite accurate. What does this mean for you?
First, let’s understand what these scales are and how they work. Bioelectrical impedance. The brief/simple explanation is that the device sends electricity through your body from one sensor to the other and measures how long it takes. More accurately it measures resistance to the electrical current.
From this information total body water can be estimated and when used in conjunction with your body mass an estimate of your body fat can be calculated.
Key words for you: estimates, body water, and speed.
Why is that important? Because there are so many variables that are being guessed that a truly accurate number CANNOT be gleaned from this method. The least accurate bio impedance is the two point setup.
Like that scale you stand on with a sensor under each foot. Two points. The next most accurate is the four point system, which is two sensors on your feet and one on each of your hands. There is also an eight point system, which as you can guess, is more accurate than the four point system.
Most people will purchase the scale you stand on, so it is safe to assume a two point system is the most common unit out there.
What will affect the signal? Water. How much water is in your body will determine the results. This is determined by a number of factors: how much muscle you have, how much fat you have, how hydrated you are, how long your limbs are, and a few other factors. Even how recently you ate or exercised will affect this.
That means that changes to any of these variables will affect the resulting reading.
The scales don’t know how long your legs are, so really, how can they know how to measure the resistance? And what if you store more fat in your abdomen? That won’t even really become a part of the measurement. Leg to leg.
What and when you eat, how hydrated you are, the length of your limbs, and a ton of other variables affect the reading and subsequent measurement.
So, no, the reading is NOT very accurate. They are notorious for UNDERESTIMATING your true body fat percentage.
Now, they can be useful for tracking changes in your body composition over time. If a person uses the same device (scale) regularly over a long period of time and averages the results you will have a fairly accurate guide as to changes in that individuals body composition.
We don’t use them. Or any other scale for that matter.
Take photos of yourself. If you like them –awesome! If you want to have less fat – eat well, exercise and in a month take more photos. If you like the changes you are on track! If not, tighten up the diet ad some more exercise intensity.
We will also use measurements such as hips, waist, chest, arms, and thighs. Measure them. In a month measure again. If they change, you are changing. Combine these with photos and you have the only body fat and weight tracking system you need.
Our base rule: if your clothes are fitting looser you are on the right track. If they are getting tighter you are heading in the wrong direction.