It’s clean. It’s neat. It’s pretty. It’s a number derived from a formula! It’s the BMI! (*cue fanfare*) For years, the BMI has been used to determine whether someone is underweight, at the ideal weight, overweight, or obese. It is calculated by dividing your bodyweight [lbs] by the square of your height [in*in] * 703. (703 is a conversion factor to modify the formula from kg/m*m to lbs/in*in) It is one of the most widely used measures of health by individuals, doctors, insurance companies, Wii Balance Boards, and our government alike – and it doesn’t amount to squat.
Having a high BMI doesn’t mean you have excess body fat – lean, healthy, muscular individuals are regularly categorized as “overweight” or “obese”. How is this possible? Because bones are almost TWICE as dense as fat, and muscle is about 18% more dense than fat. The BMI does not take into account the distribution of bones/muscles/fat within an individual. (Density figures: fat 0.9 gm/ml, muscle 1.06 gm/ml, and bone 1.85 gm/ml). Case in point, yours truly. (Sorry for the shirtless photo, but my fiancee thought it would get the point across. Thanks Paleo + MovNat for helping me look OK!)
The BMI as it is currently used in health care is a logical fallacy. We hear numbers like “66% of Americans are overweight” and “33% are obese” — but these numbers are calculated using the BMI (read: population statistics). And a high BMI has no direct causation to being unhealthy for the individual. Even though most obese people do have a high BMI, they aren’t obese BECAUSE they have a high BMI. There is more to your overall health that height and weight (as any skinny person with type 2 diabetes can tell you.) Treating the BMI as a stand-alone marker of your health, therefore, says nothing at all about how healthy you actually are.
The Birth of the BMI
You may now be wondering, where does the BMI even come from? As it turns out, the formula was created over 200 years ago to measure the degree of obesity in populations (again, not in individuals), by mathematician Lambert Adolphe Jacques Quetelet. [Quetelet explicitly stated that his formula shouldn’t be used for individuals when he presented it.]
As a mathematician, Quetelet was looking to create a statistical formula to match data he already had about the average man (the one, as Tim Ferris points out, that has 2.4 children). He was NOT a health expert looking at individuals in practice. What health-related reason could he possibly have to square someone’s height? None. But it made the numbers look better. And maybe that’s why doctors and patients alike are still so infatuated with the BMI today – it’s a clean, simple number that makes us feel like we know how healthy we are. Unfortunately, things aren’t so simple.
One telling clue of the BMI’s shortcomings is that in many current medical studies, a higher, ‘overweight’ BMI is actually associated with longer, healthier lives!
In a study that followed “ideal weight” and “overweight” individuals after heart attacks, it was shown that individuals with a high BMI were LESS likely to experience heart attack related complications, ESPECIALLY in: “…those who had a high BMI who didn’t have insulin resistance or type 2 diabetes.” How does this make sense? Because a high BMI minus insulin resistance or T2DM would point to an individual with higher bone density and more muscle mass (i.e. generally good things), not increased mid-section fat (i.e. generally a bad thing).
In another study, it was determined that men with a BMI of 26 have the longest life expectancy. This led researchers to believe that being slightly overweight was actually protective against disease, when really, it doesn’t say that at all. It just affirms that the BMI doesn’t say squat about how healthy we are. There are far better markers of health, if we wish to use them.
“Visceral fat (a.k.a. “beer gut”, “spare tire”, and “wheat belly“) is distinguished from subcutaneous fat by a large waist circumference and waist-to-hip ratio. As it turns out, the amount of visceral fat you have is far more important than body-mass index (BMI) in predicting whether you’ll develop type 2 diabetes or metabolic syndrome.” (Read more about the relationship between diabetes and weight here.)
Metabolic syndrome is the name of a group of risk factors associated with an increased risk of obesity, heart disease, diabetes, and stroke. The factors include: a large waistline (or “apple” shape), high triglycerides, low HDL cholesterol (the “good” cholesterol), high blood pressure, and higher than normal fasting blood sugar. It is estimated that 25% of the population in the United States has Metabolic Syndrome. While alarming, this number is a far cry from the 66% of overweight individuals counted by the Body Mass Index.
These factors can be tracked, not by height and weight, but by checking the aforementioned W2H ratio, triglycerides, cholesterol (including particle size), blood pressure, and A1C’s (though there is some discussion among the VLC community about the efficacy of this last test, as on a low-carb diet your blood cells actually live longer and so could give a false reading.)
Next Up, the Scale
Do yourself a favor. Go into your bathroom right now, grab your scale, and chuck it out the window. Seriously. (Okay, maybe just donate it to Goodwill or something.) In much the same way as BMI, weight alone doesn’t tell the whole story about our overall health. Started a new diet and exercise program and found you gained 5 pounds over a month instead of dropping weight? It could be that you actually put on muscle and increased bone density through resistance training. Or it could even be water weight. In the big scheme of things, 5 LBS IS NOTHING! (I invented the piano key neck-tie, I invented it. What have you done, Derek? NOTHING! NOTHING! #likethatkindofnothing)
The scale is a judge. It only can tell us about one aspect of our physical nature, and usually just serves to make us neurotic and stressed out about our weight. I’ve been there, stepping on the scale every morning and pinching my waist-line in the mirror, and I can honestly tell you the moment I put the scale out of sight, out of mind, I felt free. And with what we now know about how much stress can affect your health, it’s not worth the trouble.
A Final Note on How to Track Your Own Health
So what can you do if you’re still interested in tracking your health? Well, for starters you could go to your doctor and get some of these other tests done. But perhaps the simplest way is this: how do you look, feel, and perform? Are your strength training numbers going up? Are your distance times going down? Do you have energy throughout your day? Are you constantly sick? Do you have overt belly fat (not the imagined kind)?
If you want to get a little more down and dirty, how about taking some simple waist-to-hip measurements and some before-after photos? This doesn’t need to be done often (maybe once a month) so it’s not invasive, and will give you a much better picture of health in the long-term. Just get out a tape measurer, and measure the narrowest part of your waist and the widest part of your hips. Divide the former by the latter, and presto! Track over the long term to ensure you are trending towards healthier numbers. In women, a waist-to-hip ratio of 0.7 and in men a ratio of 0.9 is a solid indication of good health (though again, it’s not EVERYTHING) and attractiveness besides (watch from 11:50min on for details)!
How do you track progress? What’s your experience wit the BMI?
-Stay healthy everybody.