Why BMI is All Wrong: Part 1

2133

Have you ever taken a BMI test and were unpleasantly surprised with the results you received? Did your health care professional tell you that the BMI test you were taking might not have been the most accurate?

Well, as we are learning more and more about health and wellness as a society and as we are progressing in the medical and fitness fields, there’s increasing awareness on how  BMI is not a good way to measure your body fat; in fact, it is flawed.

BMI is all wrong.

Lambert Adolphe Jacques Quetelet (French: 22 February 1796 – 17 February 1874. Image from Wikipedia.
Lambert Adolphe Jacques Quetelet (French: 22 February 1796 – 17 February 1874. Image from Wikipedia.

Body mass index, commonly referred to as BMI, is based simply upon the height and weight of an individual. BMI is calculated by the mathematical equation weight in kilograms divided by height in meters squared. This equation was developed in the 1830s by a Belgian mathematician, sociologist, statistician, and astronomer named Lambert Adoplhe Jacques Quetelet. During the time in which this equation was developed, there were no calculators, computers, or electronic devices that would have been able to help calculate one’s BMI. Therefore, a simple mathematical equation was utilized to calculate BMI.

However, in this day and age with our evolution and advancement of technology, the conversation surrounding how BMI is calculated is finally being challenged. Nick Trefethen is a Professor of Numerical Analysis at Oxford University’s Mathematical Institute explains that BMI leads to confusion and misinformation. He feels that the current equation divides the weight by too much in people who are short and too little in people who are tall. As a result, tall people get a BMI result that makes them believe they are more fat than they actually are while short people get a BMI result that makes them feel they are thinner than they actually are.

Prof. Nick Trefethen FRS, Research Group: Numerical Analysis Oxford Centre for Collaborative Applied Mathematics
Prof. Nick Trefethen FRS, Research Group:
Numerical Analysis
Oxford Centre for Collaborative Applied Mathematics

Professor Trefethen argues that an equation of weight divided by height to the 2.5 power would be more accurate. He remarks, “Certainly if you plot typical weights of people against their heights, the result comes out closer to height^2.5 than height^2.”

However, he continues to wonder why the old and flawed equation for calculating BMI is still in prevalent use around the world today. He theorizes:

“Perhaps nobody wants to rock the boat.”

The Flaw in BMI

The biggest flaw in the use of BMI today arises when BMI is calculated in relation to fitness. This is because the current BMI equation does not take into consideration an individual’s lean muscle tissue content versus their body fat content. This lack of consideration leads to misleading and erroneous results for many.

The same mass in muscle weighs more than an identically sized mass of fat since it is more dense than fat. In other words, a cubic inch of muscle weighs more than a cubic inch of fat. As a result, according to current BMI calculations, athletic individuals who are very muscular will be classified by BMI as being more fat than they truly are.

For example, a six-foot tall Olympic sprinter who weighs 200 pounds might have the same BMI as someone of the same height and weight who lives a sedentary lifestyle. According to BMI, they would both be classified as overweight. While this classification might be correct for the person living a sedentary lifestyle, it would likely not be correct for the fit individual.

Don't rely on BMI alone.
Don’t rely on BMI alone.

Time for a Change

Even with the flaws of the current BMI system, major institutions continue to use BMI as a standard protocol for determining one’s body mass. According to the CDC, the Centers for Disease Control and Prevention, “BMI is a fairly reliable indicator of body fatness for most people.” The National Institutes of Health, NIH, states, “A good way to decide if your weight is healthy for your height is to figure out your body mass index.”

The good news: Doctors are starting to attack the current BMI system.

Dr. Rex Ahima of University of Pennsyvalnai Rexford S. Ahima, M.D., Ph.D., Professor of Medicine University of Pennsylvania Perelman School of Medicine. Image from Penn Medicine.
Dr. Rex Ahima of University of Pennsyvalnai Rexford S. Ahima, M.D., Ph.D., Professor of Medicine
University of Pennsylvania Perelman School of Medicine. Image from Penn Medicine.

Dr. Rexford Ahima, MD, PhD, Professor of Medicine and Director of the Obesity Unit in the Institute for Diabetes, Obesity and Metabolism remarks, “There is an urgent need for accurate, practical and affordable tools to measure fat and skeletal muscle, and biomarkers that can better predict the risks of diseases and mortality. Advances to improve the measurement of obesity and related factors will help determine the optimal weight for an individual, taking into account factors such as age, sex, genetics, fitness, pre-existing diseases, as well novel blood markers and metabolic parameters altered by obesity.”

Editor’s note: These factors are one of the reasons we recommend the Tanita body scan scale. Far better to track your muscle mass and fat percentage over just the weight on your scale.((http://mytrainerfitness.com/an-essential-piece-of-equipment-for-weight-loss-fat-loss-and-muscle-gain/))

In Part 2, we are going to take a look at better options for discerning body health and obesity.

SHARE
Previous articleThe Best Whey Protein Powders… How do you Know?
Next articleWhy BMI is All Wrong: Part 2
Kevin Martin is a Professional Writer and Certified Personal Trainer who has a passion for helping everyone reach goals and achieve dreams of positive health, wellness, and fitness. Kevin's personal writings can be found here: http://www.joshuaonenine.org