Craig Leonard

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Why BMI Measurements Are Terribly Flawed And Tell You Nothing

Craig Leonard September 13, 2014
BMI Measurement

Body mass index, or BMI, is a measurement that’s used by insurance companies and medical professionals to gauge an individual’s current health status, and overall health risk. Most personal trainers also use BMI measurements to assess the composition of their clients’ bodies.

Whether being used to establish critical markers of personal health, or to evaluate body composition, BMI measurements are terribly flawed.  Before I expose the inherent problems of using BMI measurements, let’s look at how a person’s BMI is calculated and how it’s used.

BMI is calculated by simply dividing a person’s metric weight by the square of their metric height. When using U.S. Standard units of lbs and inches a factor of 703 must be applied. Mathematically, it looks like this:

BMI Calculation Formula

Pretty simple, right? Qualitatively, BMI is used to place people into 1 of 4 categories: underweight, normal, overweight, obese.

If a person’s BMI is below 18.5, they’re considered underweight; 18.5 to 24.9 is considered normal; 25.0 to 29.9 is considered overweight; and 30.0+ is considered obese.

I’m currently standing at 6′ tall (72″), weigh 189lbs, and have a body fat percentage of approximately 12% (measured with calipers). My abs are easily visible without flexing. I’d consider myself to be fairly lean, though not shredded. By any body fat measurement standard I’m at a healthy body fat percentage for my age.

According to my BMI calculation, however, I’m considered slightly overweight at a value of 25.6. This, of course, has to do with the fact that BMI doesn’t take the composition of an individual’s body mass into consideration.

Hypothetically speaking, let’s look at what would happen to my BMI measurement if I were to add 10lbs of lean muscle mass to my body, taking me to a total body mass of 199lbs. My 25.6 BMI measurement would downgrade to a more “overweight” value of 27.0. However, my body fat percentage would have decreased and I think we’d all agree that this would be anything but a downgrade to my physical stature, bodily composition or overall health status.

I’d agree that the downgrade moving me closer toward the obese category would be completely warranted if I happened to pack on 10 additional pounds of fat, but not 10 pounds of muscle.

And that is precisely the problem with BMI. It doesn’t differentiate between muscle and fat – a differentiation that makes all the difference – making BMI a terribly flawed method for evaluating one’s health or determining how close one is to their ideal body composition.

This is why it’s completely possible for a jacked, steroid-using bodybuilder to have the same BMI as a 250lb couch potato. Or why an athlete can have a BMI that’s similar to an out of shape, skinny-fat individual, with a high amount of body fat, an embarrassingly low amount of muscle mass and a body weight that is around what would be considered “normal”.

Just as BMI isn’t a viable measurement of body composition, it’s equally unreliable when used to measure health quality, as recent research paradoxically shows that those in the “overweight” BMI category are actually at less risk of dying than those in the “normal” category.

This 2013 meta-analysis by the National Center for Health Statistics looked at 97 studies covering nearly 3 million people. The conclusion drawn by this expansive study stands in stark contrast to conventional wisdom. What this study found was that those with “overweight” BMIs were 6 percent less likely to die in a given year than those in the “normal” range. These counterintuitive results were even more pronounced for middle-aged and elderly people. This unexpected finding has since become known as the obesity paradox.

With an almost comical twist of irony, this study exposes that what the World Health Organization (WHO) derogatorily calls “overweight” is actually what is healthiest for middle-aged Americans.

It’s important to note, too, that BMI is the metric used by the National Institutes of Health to calculate national obesity statistics. We often hear about the alarming statistics showing how many Americans are overweight or obese. And, because the term “overweight” is synonymous with the term “unhealthy”, results like those shown in the following 2013 Gallup poll can be quite unnerving, indeed:

BMI Statistics of American Adults - 2013 Gallup PollIn light of this data, the impact of the 2013 meta analysis linked to above, which determined that “overweight” is actually ideal for most adults, can’t be overstated enough. What used to be interpreted as 70%+ of American adults being unhealthy (because of their “overweight” or “obese” BMI designation) can now be reasonably interpreted to be more like 35%.

Still not a number to be boasting about, to be sure, but a vast improvement from the way this data is typically interpreted and presented.

Now that I’ve discredited BMI as being a viable marker of health or bodily composition, it begs the question as to what method(s) should be used to evaluate these decidedly important metrics.

When it comes to assessing the composition of the body the only measurements we need to concern ourselves with is body fat % and lean mass. There are a number of ways to measure body fat and muscle mass – and some are more accurate than others. Still, a simple set of calipers provides you with enough accuracy that you can get a good idea of where your body composition stands in a matter of minutes from the comfort of your own home.

Here’s a post of mine that will give you more information on using calipers to assess your body’s composition.

Not surprisingly, the body’s composition and its overall level of health are intimately connected. For most people, the leaner they are the healthier they will be. Now, of course, my astute readers are decrying this advice as being dangerous.

Yes, there’s a point where an individual’s body fat becomes so low that it will shift from benefiting their health to becoming detrimental to it. Although most men and women are nowhere near being in danger of reaching this condition, men can generally maintain 6-7% body fat without it becoming a health concern. For women, the number is in the range of 10-12%.

Still, every person is different. So, if you think you may be getting so lean that it’s potentially harming your health, you should definitely see your physician to get their professional evaluation.

When it comes to overall health, the amount of belly fat a person has, in conjunction with how active they are, provides the best initial assessment of their overall quality of health. I have specifically honed in on belly fat – instead of overall body fat – because of the strong correlation between belly fat and disease.

The more belly fat a person has the higher the likelihood is that they will also have an accumulation of adipose tissue surrounding their organs. This organ-hugging fat is extremely problematic and is called visceral fat. This is why abdominal fat, in particular, is so dangerous.

A number of studies have concluded that the amount of belly fat a person has is directly related to their risk of dying from the two leading causes of death in America: Heart disease and cancer.

One such study was published in the Journal of the American College of Cardiology. The study included 3,086 people with an average age of 50. Researchers followed the study participants for as many as seven years and took note of their heart disease and cancer statuses. They also used CT scans to analyze where in the individuals’ bodies fat was accumulating.

At the end of the follow-up period, 71 people had died, 90 people had experienced a cardiovascular event and 141 people had developed cancer. After taking into account other risk factors and obesity, researchers found an obvious association between carrying fat in the abdomen and having higher risks of cancer and cardiovascular events.

WebMD also notes the link between belly fat and disease, specifically as it relates to women, as follows:

  • According to a Danish study, women who have both a big waist and high level of fats in their blood are nearly five times more likely to die of heart disease.
  • Women are twice as likely to need gallstone surgery if they have a large waistline.
  • Another study shows that women are at one-third higher risk of developing breast cancer if they have excess belly fat.

In addition to the amount of belly fat a person is carrying, the amount of exercise an individual engages in is a strong indicator of their overall health status.

In this study, researchers followed 831 veterans with type 2 diabetes for 10 years and found that the ones who exercised rarely and performed poorly on treadmill tests had a 70 percent higher death risk than those who engaged in regular exercise. Not surprisingly, the researchers’ conclusion was that an individual’s level of physical fitness provided a better indication of their quality of health than a BMI measurement.

I’m not holding my breath hoping that doctors, insurance companies and personal trainers like this come to their senses and consider abandoning the entrenched notion that BMI is a metric that holds a high level of value and accuracy for them. It doesn’t.

As I’ve conclusively shown, BMI isn’t a reliable indicator of health risk and it isn’t a reliable indicator of body composition. In fact, I can think of very little reason why anyone would bother using this terribly flawed measurement at all when there are more accurate – and just as convenient – means of assessing the metrics BMI is used to assess.

You’d be much better off focusing on the things that truly matter. I’m talking about eating a clean, nutritious, whole food diet, making regular exercise a priority, and reducing body fat to a lean and healthy level that will just so happen to make you look and feel incredible, as well.

So do yourself a favor and ditch the BMI measurement. It’s flawed beyond all recognition and tells you nothing meaningful anyway.

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