The Maintenance Library - Top 10 reasons why the BMI is bogus

07-06-2009, 10:38 AM
I saw this link from NPR and thought I'd pass it along.

Summary (the actual article has explanations of these points):
1. The person who dreamed up the BMI said explicitly that it could not and should not be used to indicate the level of fatness in an individual.
2. It is scientifically nonsensical.
3. It is physiologically wrong.
4. It gets the logic wrong.
5. It's bad statistics.
6. It is lying by scientific authority.
7. It suggests there are distinct categories of underweight, ideal, overweight and obese, with sharp boundaries that hinge on a decimal place.
8. It makes the more cynical members of society suspect that the medical insurance industry lobbies for the continued use of the BMI to keep their profits high.
9. Continued reliance on the BMI means doctors don't feel the need to use one of the more scientifically sound methods that are available to measure obesity levels.
10. It embarrasses the U.S.

Personally, I think #10 is ridiculous. Basically the author is saying that since the BMI scale says Americans are overweight, we shouldn't use it because it's embarrassing. That is frankly ridiculous. Americans ARE overweight. There's no denying it!

Some of his other points are pretty valid though IMO. Also I personally would much prefer if my doctor's office would tell me my body fat % at a physical instead of just my weight.

07-06-2009, 01:12 PM
Personally, I think #10 is ridiculous. Basically the author is saying that since the BMI scale says Americans are overweight, we shouldn't use it because it's embarrassing. That is frankly ridiculous. Americans ARE overweight. There's no denying it!

We have another thread on this in weight loss support, but this is not what he's saying. That section of the article reads:

It is embarrassing for one of the most scientifically, technologically and medicinally advanced nations in the world to base advice on how to prevent one of the leading causes of poor health and premature death (obesity) on a 200-year-old numerical hack developed by a mathematician who was not even an expert in what little was known about the human body back then.

He's saying that using a medically bogus measurement to prescribe health information, when we should really know better, is embarrassing...not that the numbers we get as a country are embarrassing!

07-06-2009, 01:33 PM
Amanda, thanks, you're right. I guess I read what I expected to read instead of what he actually said!

This issue is close to my heart at the moment since I gained just enough weight to drop me right on the line between "normal" and "overweight" on the BMI scale. I know that most of the weight I gained is muscle, and I'm far more muscular now than I was before. Based on BMI I should be trying to lose weight, but since I don't know how much of my weight is muscle vs fat, I'm not sure if it's worth it.

07-06-2009, 01:57 PM
See, that's why I think BMI is bogus...because I've been in the same position as you! Just on the low end of "Overweight", very active, small waist, healthy eating habits. I had to come to the conclusion that a "normal" BMI was not, and could not be, a sustainable goal for me. Which of course results in doctors (and the Wii Fit, :lol: ) telling me that I need to lose weight on a fairly constant basis...all based on a fairly arbitrary scale that was never intended to prescribe advice to a single individual.

How's your waist size? That's a much more solid measure of health risk than BMI has ever been, on an individual level.

07-06-2009, 02:08 PM
Applying populations measures to individuals has been a side effect of the explosion in evidence-based medicine. High quality research is fantastic. But now there's a movement realizing that what describes the population is not necessarily applicable to the individual.

07-06-2009, 02:35 PM
But if treatment with a certain medication shows that in 80% of the patients the disease is cured, I suspect that this would be a first-line treatment, no? I may not work, but odds are...given the population studies that lead to evidence-based conclusions and recommendations...I'd be taking the first-line medication, myself...



07-06-2009, 03:16 PM
Kira, it's not all or nothing ;)

07-06-2009, 04:34 PM
True, but applying the results of population studies IS valid when defining some sort of treatment rationale and basis for diagnosis. And sometimes the most common thing, population wise, is actually the truth for the individual.

As for the original post, I personally think that it doesn't matter WHAT yardstick is chosen. If we choose, say, waist size as a marker, the results would be the same. The facts are there that the American population is increasing in size, especially in the last 20 years. And this trend is something that IMHO needs to be explored, especially from a public health point of view.

BMI is just a screening tool that leads to further investigation. Whether you feel that your BMI number is valid is something to be further investigated with your MD.

The article sounds like someone just trying to shoot the messenger -- the facts are there, regardless of how they are measured. And it is a bit concerning when the intro to the piece urges Americans NOT to believe these facts because some mathematician without any training in human sciences dislikes the yardstick...

The study found that nearly two-thirds of states now have adult obesity rates above 25 percent.

But you may want to take those findings — and your next meal — with a grain of salt, because they're based on a calculation called the body mass index, or BMI.



07-06-2009, 04:44 PM
I think we may be talking about two different things.

Using BMI as a marker to study the changes of the whole population over time is a valid use of that measure. It's what it was intended for, and if you're using the same measure across the timespan, it provides a useful comparison of a large population across that timespan.

Using BMI as a specific treatment goal or guideline for a single individual is not, in my opinion or the opinion of the person who invented the measure, a valid use of that metric. It is not what it was intended for, and there are other measures that are more accurate in terms of studying individual health risk, such as waist size, and just as easy to assess.

That doesn't mean the BMI has no utility as applied to populations, but I do think it has a very limited value for a single individual as compared to other measures, from the non-invasive (waist size) to the very involved (DEXA scans, etc).

07-06-2009, 04:54 PM
Absolutely, Ms Mandalinn. Unfortunately, the headline and the intro of the article indicates that one should disregard the population studies because the concept of BMI is flawed, according to the mathematician involved.
Which is what my big beef with the article IS.
BMI is a marker, as we both point out. It isn't a diagnosis, just a marker along the way. But the population trend is important, and if you notice, the stats prompting the discussion involve the identification of OBESE people, and not those in the grey area of normal/overweight, and that one should take population studies based on BMI "with a grain of salt"...



07-06-2009, 10:53 PM
At one time, news media attempted to be impartial, or at least attempted to appear impartial. Editorials are more popular now. Apparently people don't want their information provided in "boring" news article format, they want persuasive or emotional pieces. So writers provide it, because it translates into more sales or more attention.

So we get persuasive, editorial pieces, and the reader is left to decifer the truth from the propaganda. To a degree, this has always been true, but now the job is just a little more difficult.