Dr. CĂ©line Gounder's appearance on CBS Mornings three days ago was long overdue in terms of clarifying the limits of the body-mass (BMI) index. She admitted as we've long known, it can give skewed results for athletes (like NFL Players) who have massive, muscle bound arms and legs. These guys often do register as "obese" according to the BMI - which is nonsense.
Thus, she admitted that while BMI may be useful in a "first pass" the physician then needs to dig deeper, and that means going to other metrics. She listed waist size at the top: No more than 40 inches for a male and 38 inches for a female. Also, the preference of an "pear-shape" body to "apple shape". It's thought that having a pear-shaped body — that is, carrying more of your weight around your hips and having a narrower waist — doesn't increase your risk of diabetes, heart disease and other complications of metabolic syndrome.
Back to the cockeyed BMI as an obesity measure. Ten years ago, in one of the Sunday magazines (Parade?) , I beheld a brief article (thankfully):” ‘What’s Your BMI and Why Should You Care?’ In the lead paragraph ‘the Doctors’ wrote:
“The BMI (body mass index) is a good indicator of how much
body fat you have. Health professionals use it to screen for weight problems in
adults.’
They did add that “it doesn’t paint a full picture of your
health” and that’s an understatement. As noted in a Penn & Teller ‘Bullshit’
episode at the time, lampooning BMI and the whole “obesity is an
epidemic” baloney, both Michael Jordan and Brad Pitt would be overweight, and
Russell Crowe and George Clooney would be “obese” on the BMI index scale.
Apart from such whacked out nonsense, as one Univ. of Virginia
prof quoted in the segment observed:
“Another problem with the government using BMI is that
it says everyone needs to be a certain weight within a certain height range in
order to be healthy.”
But this disdains the range of variations for most humans
pertaining to a host of attributes. It mandates that only a certain human
height-weight body profile is acceptable while labeling the outliers
“unhealthy” or “obese” or “overweight”. Using this bogus index we’ve actually
come to believe “one third of Americans are obese” – based on having a BMI of
30 or higher.
But this is nonsense!
As Penn & Teller observed it was a Belgian
polymath, Adolphe Quetelet who devised the BMI formula in
1832 in his quest to define the "normal man" in terms of everything
from his average arm strength to the age at which he
marries. Obviously and clearly, his numerical basis would be
irrelevant to today given the “normal man” ca. 1830s Belgium would not be in an
way comparable to the normal man today - especially in the US of A. His diet
would be more frugal, less protein for one thing as well as fewer nutrients, and
hence he’d naturally bear more a resemblance to reed-thin Stan Laurel than
George Clooney, or Russell Crowe.
So his project had nothing to do with obesity-related
diseases, nor even with obesity itself. Rather, Quetelet used the formula to
attempt to describe the standard proportions of the human build—the ratio of
weight to height in the average adult- in that reduced nutrition era. Using
data collected from several hundred countrymen, he found that weight varied not
in direct proportion to height (such that, say, people 10 percent taller than
average were 10 percent heavier, too) but in proportion to the square
of height. (People 10 percent taller than average tended to be about 21
percent heavier.)
The new formula had little impact among the medical community until long after
Quetelet's death. While doctors had suspected the ill effects of obesity as far
back as the 18th century, their evidence was purely anecdotal. The first
large-scale studies of obesity and health were conducted in the early 20th
century, when insurance companies began using comparisons of height and weight
among their policyholders to show that "overweight" people died
earlier than those of "ideal" weight. Subsequent actuarial and
medical studies found that obese people were also were more likely to get
diabetes, hypertension, and heart disease. (Of course, this later allowed
the medical insurers to either invoke "pre-existing conditions" to
bar people from coverage or, more often, have an excuse to increase their
premiums.)
By the early 1900s, it was fairly well-established that these ailments were the
result of having too much adipose tissue—so the studies used functions of
height and weight as little more than a proxy for determining
how much excess body fat people had. The problem with proxies, of course,
is that they are not direct quantifiers or indicators and are only so good as
the physical basis really allows.
It would actually have been more accurate for the actuaries to
compare longevity data with more direct assessments of body
fat—such as caliper-measured skinfold thickness or hydrostatic weighing. But
these data were much harder for them to obtain than standard information on
height, weight, and sex. So they punted!
Medical researchers , meanwhile, needed a standard measure of fatness, so they
could look at the health outcomes of varying degrees of obesity across an
entire population. For decades doctors couldn't agree on the best formula for
combining height and weight into a single number—some used weight divided by
height; others used weight divided by height cubed.
It arrived in 1972, when
physiology professor and obesity researcher Ancel Keys published his "Indices
of Relative Weight and Obesity," a statistical study of more than
7,400 men in five countries. Keys examined which of the height-weight formulas
matched up best with each subject's body-fat percentage, as measured more
directly. He concluded that the best predictor came from Quetelet’s BMI: weight
divided by height squared. Keys renamed this number the body mass index.
But this was decidedly premature.
A critique (in PDF) of the body mass index in the
journal Circulation suggests that BMI's imprecision and
publicity-friendly cutoffs distort even the large epidemiological studies. (For
example, there's no definitive count of how many people are misclassified by
BMI, but several studies have suggested that the error rate is significant for
people of certain ages and ethnicities. That old natural variation bugbear
again!) It's impossible to know which studies have been affected and in what
direction they might have been skewed.
Further, the BMI is actually a solid example of the “proofiness” that Charles
Seife referenced in his book, Proofiness: How You're Being Fooled by
the Numbers.
Seife decries the tactic of using numbers not just to lie but
to baffle the susceptible with bullshit. He refers to a common
failing of most people unversed in math to be hoodwinked merely because some
form of math or numbers are interjected into arguments. Not just
using numbers to bolster one's argument. In his words, to use fake numbers to
prove falsehoods and to seek to prove something is true - even when it's not-
is one of the most egregious forms of intellectual fraud.
In this regard, one of the surest signs of proofiness is the
failure to provide attached uncertainties to the measurements - any
measurements! Since BMI is always recorded as an absolute single number,
say 29, and never as 29 + 2 or whatever, then
it is inherently proofy - a bogus quantity. Seife emphasizes there can NEVER be
a 100 percent accurate number if based on physical measurements, and he's
right. Maybe the scale used is off by a pound or two, and maybe the height isn't
evaluated for the associated probable error - based on the instrument used
to measure it. OR......maybe, just maybe the presumed cutoffs along
the BMI chart indices have been majorly distorted by earlier
misclassifications in large epidemiological studies.
The BMI also takes this to new level because the
combination of the 2 quantifiers make no sense. I mean the ratio
of weight in pounds to height in inches squared? And then
multiplying by 703? That’s pure baloney and in no way even comparable to say
obtaining metric mass by dividing the weight (in newtons) by the acceleration
of gravity in N/kg.
Where does 703 come from anyway? Well it’s the correction factor introduced if one used Imperial units (foot, pounds) in stead of metric system. In the metric system the BMI is simply:
Mass (kg)/ [height (m)]2
Again, this is bollocks, since the result (mass per unit area) yields no conceptually consistent physical quantity as applied to human biology! It’s fully an example of more proofiness: In this case putting two unrelated units together in a ratio and making people believe the result (in kg/m2) has some innate core physical meaning. It doesn’t. It’s bullshit. (As Penn and Teller also pointed out in their show on “Obesity”.)
The medical -industrial -insurance- PhrMA whackos will try to tell you the ratio is valid because height and weight "are related", but this is a presumption unwarranted by the total constellation of data- especially applied to distinct ethnic groups. Also, if one investigates the fundamental units of physics that comprise it, s/he will find no such equivalent anywhere. (Which can also be deduced by using the basic SI units in various combinations.)
The closest one can come is the combination of units:
kg m -3 Which is mass divided by the length cubed or M L -3
This yields what we call “density”. And at least the use of density would make some physical sense, but the ratio for BMI makes zero sense, because no comparable physical quantity in terms of mass per unit area exists for human bodies. It make no difference how many idiotic trials were used to attempt to validate it in the health sense.
I could as well take the Martian mass in kg, and divide it
by its assorted Earth opposition values in meters to show that UFO
sightings increase whenever the ratio approaches a certain value (say 1013 kg m-1.)
It is pure nonsense, and any “findings” add up to little more than lucky
coincidence.
The use of this dumb obesity quantifier is even more enraging
given there’s at least a more rational alternative. It turns out that the circumference
around a person's waist provides a much more accurate reading of his
or her abdominal fat and risk for disease than BMI. One unit, no hocus pocus.
Simple. Besides, wrapping a tape measure around your belly is no more expensive
than hopping on a scale and standing in front of a ruler. That's why the
American Society for Nutrition, the American Diabetes Association, and other
prominent medical groups have lately promoted waist circumference as a
replacement for, the body mass index. (Some have indicated as a “supplement” but
why waste time with proofy contrived numbers at all?)
Alas, few doctors - including our own - have made the switch. This
is probably because waist measurements require slightly more time and training
to interpret than it takes to record a BMI reading and use some fake
out chart, which doesn’t come with any “official cutoffs”. (Right now, my BMI
is 29.5 but I laugh when anyone says I am “over weight” for the reasons given
above, especially the proofiness of the index and nonsensical
units.) The sensitivity of doctors to these slight inconveniences
signals just how difficult it will be to unseat Quetelet's antiquated and
irrational, proofy formula. See, the body mass index is cheap and easy to get
(never mind the absence of uncertainty), and it has the incumbent advantage in
that the Lords from On High in Health Central have conferred their benediction
– along with the political-Pharma –lobby enclave – so who’s going to argue with
them? Well, I am!
Sadly, just like tea leaves, natal horoscopes and palm reading, BMI is here to
stay—despite its flaws – the chief of which is that it’s irrational and has no
bearing to any real physical quantity (as the examination of its units
discloses)
But that doesn’t mean I have to treat it any more seriously than other monkey fool bollocks, including horoscopes, palm reading and tarot cards.
As for rationality in terms of obesity these are the
key obesity- BMI myths you need to know, summarized from
Prof. Paul Campos in his book, 'The Obesity Myth':
1) Weight is a good proxy for health ("97 percent
false" according to Campos)
2) Health improvement comes via transition from being fat to
thin. (Hardly ever, for most people - especially the elderly who are more at
risk if they become frail.)
3) We know how to produce long term weight loss.
In respect of the last, Prof. Campos makes it clear that
despite the bloviations of the medical-industrial-insurance complex and the
government health brigade as well as the health diet faddists, no one really
has a clue how to sustain long term weight loss. Yes, they say, "balance
intake of food with exercise" -but if a lot of weight gain is traced to
gut bacteria this is a non-starter.
Then there is the leptin factor, which hormone levels decrease when
people don't get enough sleep - and which causes them to eat inordinately. As
explained on one medical site (WebMD):
"When you don't get enough sleep, it drives leptin levels down, which
means you don't feel as satisfied after you eat. Lack of sleep also causes
ghrelin levels to rise, which means your appetite is stimulated, so you want
more food,"
The sad fact is too many overworked and tech over- connected
Americans are in this latter category. Dieting won't help them but getting on a
regular, decent sleep schedule might!
Stay tuned, and in the meantime don't get hysterical over your
BMI!
