Why BMI is All Wrong

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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.1)http://mytrainerfitness.com/an-essential-piece-of-equipment-for-weight-loss-fat-loss-and-muscle-gain/
Now that the negative aspects of BMI have been described in detail, we can objectively ask the question, what’s a better way to discern body health and obesity, if not BMI? The opportunity to investigate different alternatives to BMI will allow us to gain a better understanding of ourselves and our bodies so that we can more readily address our current health and our possible future health concerns.

As new medical technologies and thought processes are being developed, there are exciting methods emerging to help us better measure one’s body fat.

BAI

One such advancement is known as BAI, or Body Adiposity Index. BAI differs from BMI in that it does not use body weight in the calculation of its figures. Instead, BAI multiplies hip circumference by height to obtain the percentage of body fat. In areas where scales may not be readily available, this method of body fat testing is regularly used. It is thoroughly believed that the BAI method for testing body fat is more accurate than BMI, although clinical studies have not shown any evidential proof.

BAI: Hip Circumference x Height = Body Fat Percentage.

Richard-Bergman-photo
Richard Bergman, PhD, Director, Diabetes and Obesity Research Institute

Richard Bergman, a Professor of Medicine at the University of Southern California in Los Angeles who focuses his research on obesity and type 2 diabetes, believes that it is time to do away with the old and outdated BMI system by ushering in the new BAI method.

Bergman is one of the leaders behind the BAI movement. Through his research findings, he states, “It turned out that hip circumference and height were more correlated with percentage body fat than anything else, including waist circumference and height. So we designed an equation that could take both of these into account. We call this the Body Adiposity Index.”

He continues, “It turns out that BAI is a good predictor of percentage adiposity, so if your BAI is 30, then your percentage body fat is around 30 per cent. It is reasonably accurate – not terribly accurate – but usable as a clinical tool.”

With this increased comprehension of what BAI means and how it is calculated, it can be understood how this method of body fat testing has the possibility to be more productive than the long time use of BMI.

When asked if BAI is better than BMI, Bergman responded, “We think it’s better, but we have still got to prove it. Unlike BMI, the BAI for men and women is the same if they have the same percentage body fat. We have validated the BAI in African American populations too. Its utility has not been confirmed in Caucasian subjects, although we have tested it on a small group and it seemed to fit.”

shutterstock_327075548

Like anything, BAI has its downsides in addition to its upsides. Relating to the downsides of BAI, Bergman explained, “The real challenge is to be able to predict the risk of obesity-related diseases such as cancer, diabetes, cardiovascular disease and hypertension, and then to intervene. It remains to be shown that BAI is a more useful predictor of these outcomes than other measures of body adiposity.”

With these understandings in mind, it would behoove you to take precaution if planning to rely solely on the BAI test. Since it is not clinically medically researched, you should proceed with caution with the test, especially if the test is going to be your only means of body fat testing (we recommend you utilize a variety of methods) and if you are at risk for the above health conditions.

Still, BAI is looking to be a promising improvement for body fat testing. Bergman is hopeful that BAI is better than BMI and will one day succeed BMI as a measure of obesity because BMI is often used incorrectly by a large number of medical practitioners who are unaware and do not realize that BMI is a poor measure of one’s body fat percentage.

Editor’s Note: math is not our thing and isn’t something we have much patience to slog through, so we didn’t spend much time sorting out the formula on Wikipedia, however, it’s here if you’d like to.2)https://en.wikipedia.org/wiki/Body_adiposity_index Meanwhile, there’s no need to bend your brain if math’s not your thing as there are several cool BAI calculators at the ready, such as this one on ShapeSense.com.3)http://www.shapesense.com/fitness-exercise/calculators/body-adiposity-index-calculator.aspx

We found our BAI percentage to be a bit off from our Tanita body composition monitor.4)http://mytrainerfitness.com/an-essential-piece-of-equipment-for-weight-loss-fat-loss-and-muscle-gain/The BAI calculator showed over 1% more in fat than the body scan, which we’ve found to be fairly consistently reliable.

The other issue we have with BAI is the premise of measuring the hips alone. Depending on the body type, there are definitely those who store most of their fat in their hip area and conversely, definitely those who have slim hips but store their fat in their gut and abs. Men are especially prone this way, but some women as well, so anyone In that latter category, (storing fat in the stomach), would show up as lower in fat than they actually are, while those who are hip storers might show up as having a  higher fat percentage than they do overall. Now this could even be dangerous since we know that abdominal fat tends to be a more dangerous fat for the heart and organs and even in the production of cancer cells. SO… we’re not yet convinced that BAI is a good thing. What do you think? We’d love to hear your thoughts via email or comments on the My Trainer Fitness Facebook page


Meanwhile, there are additional alternatives to BMI. These alternatives to BMI and BAI include Waist Circumference Measurement (WCM), Waist-to-Hip Ratio (WHR), Hydrostatic Weighing (HW), and Body Fat Measuring (BFM).

Waist Circumference Measurement

shutterstock_248712676

The Waist Circumference Measurement is one of the most effective alternatives to BMI because of its simplicity. This measure utilizes only an old fashioned tape measure. The test is carried out by doing a measure of the natural waist. This measurement of the natural waist gives a good and reliable indication of the actual amount of abdominal body fat.

Women with a waist circumference that is greater than 35 inches and men with a waist circumference greater 40 inches

The knowing of waist circumference is helpful knowledge in determining possible risk of heart disease among with other medical conditions. Women with a waist circumference that is greater than 35 inches and men with a waist circumference greater 40 inches are both indicated to be in the “at risk” category, according to physicians.

Editor’s Note: As indicated in our comments under the BAI section, again, it doesn’t seem practical to base this measurement as valid for all people give the different body compositions and body types.

WHR — Waist-to-Hip Ratio

The Waist-to-Hip Ratio measurement is beneficial for numerous reasons. The calculation is useful for determining the amount of excess weight that is being carried around by an individual and is also useful as an indicator tool for various serious health issues, such as high blood pressure, heart disease, and diabetes.

The Waist-to-Hip Ratio is easily calculated by using a simple tape measure. The natural waist is to be measured along with the widest part of the hips. When these two measurements are obtained, the circumference of the waist is to be divided by the measurement of hip circumference. The calculated result that is given is then to be compared with a specified chart that is based upon the standards that have been set by the German Society for Sports Medicine and Prevention (DGSP).

WHR: Waist ÷ Hip = Result

WHR — Waist-to-Hip Ratio results plot is as follows:

Normal Weight:
Men: < 0.90
Women: < 0.80

Overweight:
Men: 0.90 to 0.99
Women: 0.80 to 0.84

Obese:
Men: 1.0+
Women: 0.85+

So for a woman with a 30″ waist and 39″ hips the calculation would look like this:

30″ waist ÷ 39″ hips = .769 for a result rate of of 76.9% and would be categorized as “normal”.

HW — Hydrostatic Weighing

Hydrostatic weighing is a process for determining body fat that has been debated in the recent years on its effectiveness. It has been shown to be highly effective for many individuals, however it’s certainly not an easy test to do. Put simply:

Hydrostatic weighing is a direct application of Archimedes’ principle, that an object displaces its own volume of water.5)https://en.wikipedia.org/wiki/Archimedes%27_principle

The hydrostatic weighing process takes places underwater on a chair placed on a set of scales, (or in a special tub scale. The scales are zeroed out. A unique process follows where the individual being tested sits on the chair and then exhales as much air from the lungs as possible and places his or her head underwater. At this moment when the scales stabilize, the weight of the individual is taken. Once the weight is gathered and determined, the numbers are passed through a series of formulas that will produce a body fat reading.

Even though this process can be beneficial to many, there are many downsides and downfalls to the method. Perhaps the biggest obstacle is obtaining the resources to complete this method. Since there are many large pieces of highly-specialized equipment involved, the hydrostatic weighing body fat test is one that will not be readily available to the masses. This makes the hydrostatic weighing method difficult to understand as a widely-utilized method because it is very limited in its availability, compared to other methods like BAI, Waist Circumference Measurement, and Waist-to-Hip Ratio which are more accessible to the everyday user.

If you’re really interested in this the hydrostatic body weight test, there are places—often mobile units—that travel around and run this test for you. When you have this option, then it’s not a big deal.

Here’s an example of that—in detail—in this video from BodyFatTest.com.6)http://www.bodyfattest.com/


Body Fat Measuring

The last major alternative to body fat testing is body fat measuring. This method is known as being one of the most simple methods to testing body fat; all that is needed to complete this method is a special set of calipers.

With this test, skin and fat measurements are taken, using the calipers, from the waist, shoulder blade, biceps, and triceps. The locations on the body where the measurements are to be taken differ for men and women. Additionally, this test, also known at the Jackson-Pollock Method, can be completed with three, four, or seven different locations on the body to get an accurate representation of one’s body fat.

Dr. Andrew Jackson, professor emeritus.7)http://www.uh.edu/class/hhp/people/emeritus-listing/andrew-jackson/

The Jackson-Pollock 3 point method can be completed using a minimum of 3 skinfold measurements from any of the following locations on the body:

For men:
  • To gather the pectoral measurement, obtain a diagonal skin fold that is halfway between the nipple and the upper portion of the pectoral muscle from the armpit.
  • For the abdominal measurement, take a vertical fold of skin that is one inch to the right of the belly button.
  • Lastly, for the thigh measurement, a vertical fold of skin is to be taken that lies halfway between the knee cap, or the patella, and the inguinal crease, the location where the top of the thigh connects with the hip.
For women:
  • The triceps measurement is to be a vertical skin fold that is taken halfway between the top portion of the shoulder and the elbow.
  • For the suprailiac measurement, take a diagonal skin fold measurement above the the superior anterior iliac crest, or the area above the upper and forward protrusion of the hip bone.
  • Lastly, the thigh measurement is to be a vertical skin fold taken halfway between the knee cap, or the patella, and the inguinal crease, the location where the top of the thigh connects with the hip.

The Jackson-Pollock 4 point method is to be completed with four locations on the body. For this method, the body locations are the same for both men and women. The locations, with the same descriptions as listed above for the corresponding measurements, are the triceps, suprailiac, abdominal, and thigh.

Take a look at this visual representation of the locations for the Jackson-Pollock 4 point method:

 

male-4site-Jackson-Pollock

The Jackson-Pollock 7 point method is to be completed with seven locations on the body. Similarly to the four point method, this seven point method utilizes parts of the body that are both the same for men and women. The seven points are:

  1. Axilia
  2. Chest
  3. Abdominal
  4. Sub scapular
  5. Surailiac
  6. Tricep
  7. Thigh

For a visual representation of these locations, see the photo below:

 

female-7site-Jackson-Pollock

Tanita Body Monitor

Here at My Trainer Fitness, we really like, use and recommend the Tanita Body Monitor as a powerful and accurate way to measure various aspects of your body for immediate results, showing you the progress you are making toward your health and fitness goals.

The Tanita Body Monitor can be purchased in different models. My Trainer Fitness has two.

The first that we have is the Tanita BC-558 Ironman Segmental Body Composition Monitor. This monitor has the following features:

  • Weight
  • Full body fat %
  • Segmental body fat% (including right arm, left arm, right leg, left leg, and trunk)
  • Total body water %
  • Full muscle mass
  • Segmental muscle mass (including right arm, left arm, right leg, left leg, and trunk)
  • Physique rating
  • Basal metabolic rate
  • Metabolic age
  • Bone mass
  • Visceral fat
  • Automatic scrolling or results: weight, body fat% and segmental body fat %
  • Recall function: weight, body fat %, body water %, muscle mass, BMR, bone mass and visceral fat
  • Graph function for: body fat % (total and segmental), body water %, bone mass, visceral fat and BMR
  • Graph recall: calendar days / 52 weeks / 36 months
  • Clock & calendar
  • Backlit icon buttons
  • Guest mode
  • Weight only button

The second model we have is the Tanita RD-901 BK Ironman iPhone Scale, which links to the Apple iPhone. This model includes the following features:

  • Weight
  • Body fat %
  • Body water %
  • Muscle mass
  • Physique rating
  • Basal Metabolic Rate
  • Metabolic age
  • Bone mass
  • Visceral fat
  • BMI
  • Weight only button
  • 4 users
  • Guest mode included
  • Includes gravity setting for greater accuracy

Tanita Body Monitors are practical investments for your health and fitness. In fact, many of our bodybuilder friends recommend this product for its ability to capture their results in detail.

We’ve written more about this here8)http://mytrainerfitness.com/an-essential-piece-of-equipment-for-weight-loss-fat-loss-and-muscle-gain/

With the awareness of all the new alternatives methods to determining and calculating your body fat, you now have better options that will be more beneficial to you than the flawed and outdated BMI calculation. Let us know what you’re using and why by joining the conversation and commenting on the My Trainer Fitness Facebook page.

Resources:

4-Site Body Fat Calculator (Jackson-Pollock Formula) UPDATED, BurnTheFatInnerCircle.com9)http://www.burnthefatinnercircle.com/members/Jackson-Pollock-4-site-skinfold-calculator.cfm

5 Alternatives To Body Mass Index (BMI), TheCalculatorSite.com10)http://www.thecalculatorsite.com/articles/health/alternatives-to-bmi.php

An Essential Piece of Equipment for Weight Loss, Fat Loss, and Muscle Gain, MyTrainerFitness.com11)http://mytrainerfitness.com/an-essential-piece-of-equipment-for-weight-loss-fat-loss-and-muscle-gain/

Mens Percent Body Fat – Jackson/Pollock 4-Site Caliper Method, Unit-Conversion.info12)http://www.unit-conversion.info/othertools/4-site-mens-percent-body-fat/

Obesity expert: A better fat measure than BMI, NewScientist.com13)https://www.newscientist.com/article/mg20928030-200-obesity-expert-a-better-fat-measure-than-bmi/

Womens Percent Body Fat – Jackson/Pollock 7-Site Caliper Method, Unit-Conversion.info14)http://www.unit-conversion.info/othertools/7-site-womens-percent-body-fat/lth and obesity.

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