BMI versus Body Fat Percentage?

BMI-vs-Body-Fat-AdvoCare - Jonathan Weiner

Body Fat Percentage versus BMI?

When you get past the point of just dropping scale weight, e.g. muscle and fat, and you're truly trying to focus on body composition for overall health, fitness level, you need to be able to properly measure your body fat percentage. First, let me explain what BMI, Lean Weight and Body Fat Weight mean. BMI stands for Body Mass Index which is a simple measure of the weight of a person scaled according to their height. It doesn't factor in a lot of other components such as muscle and body types (endomorph, ectomorph and mesomorph). Lean weight is your muscle, organs, and bones which is basically everything except your body fat. Body Fat is extremely important. We live in a culture that demonizes body fat, however, it is actually essential for the human body to function properly. It helps protect our internal organs, regulates body temperature, and produces vital hormones and chemicals. It has many other roles that keep us alive and healthy but being in a certain range based on your fitness goals and levels is actually what this number is all about. Here are the guidelines for body fat percentage.

Ok, so once you know where you want to be, the question becomes how to measure body fat accurately. Here are the methods and my personal experiences with or without them.

Ideal-Body-Fat-Percentage - Advocare Jonathan Weiner

Body Fat Scales
Body-Fat scales use a technology called bioelectrical impedance to estimate how much body fat you have. When you step on sensors on the scale, an imperceptible electrical current passes up one leg, across the pelvis and then down the other leg. Because it contains much more water, muscle conducts electricity better than fat does, so the greater the resistance, the more body fat you have. The scales use formulas to calculate a body-fat percentage from this resistance information, along with other data that you enter (height, weight, age, gender). Some also include hand electrodes to better estimate overall body fat and an increasing number come with fancy features such as wireless transmission of data to your computer. Because the electric current passes through only your legs, the scales might underestimate body fat if you have a big belly but slimmer legs and overestimate it if you carry more weight on your hips and thighs. Results can also vary depending on whether your feet are wet or dry (they should be dry, according to the instructions), whether you recently exercised, and how much water you had to drink. And the devices don’t work well if you have an artificial hip or knee because the man-made materials can interfere with the electric current. They are extremely inaccurate with variances of 16-45% off.


DEXA is often referred to as the “gold standard” of body fat measurement, but research shows that it can be just as wrong as any of the other methods on this list. Here’s why DEXA isn’t as great as many people think.  The machines’ accuracy is affected by a number of variables, including gender, body size, body fatness, disease state, and hydration state.  Different machines rely on different algorithms to convert the raw data into a body fat percentage, and some are better than others.  The X-ray type (i.e. fan or pencil beam) affects the test’s accuracy.  Different machines can produce different results—even two machines made by the same manufacturer.

Unfortunately, there’s just no way to know if the results of a DEXA scan are truly accurate.

Bod Pod
The science behind Bod Pod testing is similar to hydrostatic weighing. You take a seat in a sealed chamber and sensors measure the amount of air that’s displaced by your body. Then, the readings are plugged into various equations that provide you with different body composition measurements. Well, we already know that hydrostatic weighing often yields faulty measurements, and it appears that the Bod Pod is even less accurate. Its readings can be influenced by many factors, including body temperature, facial hair, moisture, and even the tightness of a person’s clothing. Given all these variables, it’s no shocker that studies have found the Bod Pod to have rather large error rates. In one study, the test was off by up to 15 percentage points. In other research, error rates were up to 5 or 6 points.  I can also vouch for the Bod Pod’s inaccuracy.

Skin Fold Caliper Measurements
As a general rule, if your skin is getting thicker over time, you’re getting fatter. If your skin is getting thinner, then you’re getting leaner.

Here’s why I like this caliper. It utilizes one-site testing, which means you can do it yourself and there are fewer chances for making mistakes. Its body fat measurements are surprisingly accurate. This is the website I use and the one my trainer uses on me, click here. There are 5 different skin fold caliper tests you can use. We use the Jackson/Pollock 7.

What is the correct or ideal % body fat?  This is perhaps the most difficult question to answer.  Not all people have the same ideal % body fat. It varies with age, sex, and genetics.  One person might be better at a higher or lower body fat than another person of the same age and six. And the desirable body fat of athletes can vary depending on the sport. For example, swimmers seem to perform better at a higher % body fat than runners.

There’s really no way to calculate body fat percentage with 100% accuracy. The point is every method out there for assessing body fat percentage is an estimation. And as you’ve seen, some are better than others but none are as great as we would like to think. But at the end of the day, Skin Fold Caliper would be your best bet and the most affordable.

Body fat percentage is a much more accurate measurement in determining if you are healthy. BMI doesn't take into consideration how much of your weight is muscle and bone and how much of it is fat. So that means a person can have a healthy BMI, but can still carry weight in their belly, which can increase their risk for heart disease. So if you're trying to lose weight, or just wondering if your current weight is healthy, it's worth seeing someone to have your body fat percentage measured.