BMI: Truth or Lie?
Thu, Oct 15, 2009
I’m going to talk about Body Mass Index (BMI). Basically, your BMI number is a number that’s used by physicians to categorize people into proportional weight classes in relation to their height.
There are several categories that are used: underweight, normal, overweight, and various classes of obesity. I’ve included another one of my high-tech diagrams below to illustrate the levels with the corresponding numbers:
Also, here’s a diagram discussing the risk of death.
Image Credit: FitnessCampus.com
This is the general idea with BMI: the closer to a BMI of 25 we are, the less risk of disease and death. Now, one area that I might contend with is where the lowest risk of mortality is located. I have seen research while in school that it’s around 26 (in overweight), but without finding the article for myself I can’t confirm this. But the concept is the same, the more deviation from a normal BMI, the higher risk of disease and death we face; more so in the higher BMIs.
BMI isn’t the be-all-end-all, however. There are some people where a BMI isn’t accurate for them. People that may be in the obese category could be muscular athletes. So the Arnold Schwarzenegger’s out there may have a BMI of 33, but aren’t obese. The opposite goes for elderly adults where their muscle mass is way down and replaced with fat, but their BMI underestimates it, say at a 22. So BMI is really a quick and dirty way to categorize our weight class as compared to a typical population.
Tactics that may be more accurate are measuring circumferences and taking a ratio between the waist (belly button height) and hips (mid-gluts/buttocks). There are also very accurate measures, like using calipers and bioelectric impedance (which measures fat and muscle by using electrical conduction). This is very accurate, but expensive, equipment.
So the first tool to use may very well be the BMI. You can calculate it yourself: BMI = (pounds x 703)/(inches2) OR kilograms/meter2. Or, you can just go here to calculate it and find out more.
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Tags: physical examination, weight
Great Post James ! Very informative. I think more people need to understand what and how their BMI relates to their health and well being. It is important though, as you pointed out, that it is only a guideline and not to take literally. As there are many factors; such as, different skeletal frame sizes, muscle mass, and body types.
I typically find that a “normal” BMI of 18.5 to 24.9 to be a little under weight for most and recommend to most of my patients to try and be between 25 to 29.
Thanks for the comment, Dr. Heins.
We do have to realize that the BMI isn’t the be-all-end-all. The numbers have to be adapted to the patient, I feel that most of the time this works. Personally, I feel that a more “Normal” normal is probably around 22-27. Obviously, we shouldn’t just rely on BMI, we should include other measurements like I mentioned in the post.