Weight is an important wellness issue for the Human population, because too many people are over-weight, and because our (American) culture is obsessed with “weight” as a predictor of social success [and therefore of the probability of contributing genetic information to future generations, which is known to be an important driver of behavior in animals]. More importantly, weight has been shown to have a statistically significant relationship to life expectancy [still the average age at which 50% of an even aged population will die]; Actuarial Science studies the statistical relationship between geographical, biological, sociological, and psychological factors and probability of death, where probability of death is “interesting” to life insurance underwriters, and they have documented the relationship of weight relative to height as a predictor of premature death [“defined” as any death which occurs before enough premiums have been collected to cover the cost of paying the death benefit].
Actuarial scientists have documented that weight relative to height stastically predicts life
expectancy, and therefore can be used to estimate “insurance risk” or the amount
underwriters of life insurance policies can expect to pay out over the term of a class of policies
(from which the underwriters calculate the amount they must collect in premiums to ‘break
even’ [they make money by investing the premiums between the time premiums are collected until
death benefits are paid]). This led to medical professionals developing weight to height charts
1. under weight [more than one standard error below average],
2. normal weight [within one standard error, plus or minus, of average], and
3. over weight [more than one standard error above average].
However, you need to know that these charts, hanging in general practitioners' examining rooms, report statistical summaries of large populations (and not the same information [risk of premature death] as the actuarial charts). The chart in the doctor's office merely compares the patient to “the average American.” [note: the “average American” is a statistical construct and is approximately 50% male and 50% female; I personally have never met this hypothetical person]. Since the general population of the United States has been getting progressively heavier over the last 60 years, these charts keep shifting to higher weights as ‘normal,’ and the resulting charts say nothing about desirable weight for your height.
Recognizing the problems inherent in the statistical summary versions of weight - height charts, medical researchers tried to develop a single value index which could be used to evaluate wellness risks associated with excessive weight. The result was the Body Mass Index (BMI), which is “relatively easy” to calculate:
BMI = weight (kilograms) divided by height squared (meters2).
However, we [Humans in the United States] weigh ourselves in pounds, and measure our heights in feet and inches. So we have to convert:
BMI = weight (lbs) divided by height (as 12 X ft + in), then divided by height again, and multiplied by 703 [the conversion factor for lbs/in2 to kg/m2]. The resulting number, the BMI, can be compared to a chart to evaluate the your ‘weight status.’ Note: “obese” is a diagnosable medical condition, and can only be diagnosed by a licensed diagnostician (such as MD or licensed Nurse practicitioner), so you aren't obese until a Doctor says you are.
|underweight||under 18.5 kg/m2|
|normal||18.5 - 24.9 kg/m2|
|overweight||25.0 -29.9 kg/m2|
|obese||30 kg/m2 or higher|
BMI is not without its own problems. At the peak of his wrestling career, Arnold Schwarzenegger
was ‘obese’ according to the BMI guidelines, yet his body fat percent was near [or below]
the minimum acceptable value. The CDC (Centers for Disease Control) reports
(www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html) that, for non-athletes, the BMI
correlates (statistically) well with body fat estimated by more technological, and expensive,
methods. As the CDC points out, the weight and height of patients is routinely collected by Nurses
working for general practictitoners, so there is a very large database of weight - height data (and
a very small data base of “better” estimates of weight as a risk factor for compromised
wellness or even premature death).
The “best” predictors of weight as an issue in wellness and life expectancy are amount (volume) of and location of adipose tissue. The most precise [defined statistically as the repeatability of an estimate, see “Introduction to the Content” lecture] estimates of fat content of the body are MRI, CAT scan, and DEXA scan, which involve large, expensive high-tech equipment requiring highly trained technicians and radiologists. These are not practical for determining wellness… neither patients, nor their insurance underwriters, would be willing to pay for such testing. Next best would be underwater weighing, where the patient is suspended in a sling and weighed, then lowered into a swimming pool and reweighed. The lost weight in the water is due to bouyancy (and fat is bouyant; lean body mass is not). Most of the patients who have routinely agreed to this process were paid volunteers [mostly college students at residential campuses] in health and wellness research studies. And finally, we come to a method which is simple enough to actually use - bioelectrical impedance. While the patient is lying on the examining table, electrodes are attached to the ankles and wrists. A low voltage current is run through the patient's body to measure resistance to the flow of electricity. Fat is not a good conductor, but lean body tissue is; unfortunately water is an even better conductor, so this method is highly sensitive to hydration [you can ‘change’ your fat percentage by drinking a few glasses of water], and can vary by as much as 3 percentage points within a single day [data collected by Dr LaFrance using inexpensive bathroom scales capable of measuring resistance from one ankle to the other on a sixty-something male weighing approximately 157 lbs]. This method is not very precise (plus or minus 3%) yet research has now shown than the home scales are accurate [the measured value is statistically the same as values from high-tech devices]. The next best method is taking three measurements of circumference of the torso (see below). Not quite the worst method, but close, is skinfold thickness [“pinch an inch”] using calipers [most people not only don't own calipers, they probably don't know what calipers are, unless they are factory workers who use calipers for quality control measurements]. The winner of the worst method of determining whether or not weight is a problem is the standard bathroom scales, which is supposed to tell you how much you weigh. This instrument has exceedingly poor precision. Try this experiment yourself. Look at your bathroom scales; does it read 0.0 lbs [my old mechanical (spring) scales read 0 plus or minus 3]. Now step on the scales [you don't even have to read your weight], and step back off. Now what does the scale read; is it 0.0, or some other number [my old scales changed the zero point by as much as 5 lbs by my stepping on then off; this is why the package states “NOT LEGAL FOR TRADE”]. As for BMI, there are charts available showing desirable body fat for different groups of people:
|Percent Body Fat guidelines|
|10% - 12%||  2% -  4%|
|athlete||14% - 20%||  6% - 13%|
|fitness||21% - 24%||14% -17%|
|acceptable||25% - 31%||18% - 25%|
|obese||≥ 32%||≥ 25%|
Skinny young adult women might be shocked to learn that they have 3 to 5 times as much (by
percentage) fat as their male counterparts, but the rest of you have probably already noticed that
men tend to have less fat than women do. It's not luck that we (men) have less fat, it's evolution
of the type called sexual selection, which (in English) simply means
that men are attracted to strangely [compared to other mammals] located fat deposits on women, while
women do not find body fat to be attractive on men. Many
textbooks try to pretend than higher fat content of women is there to feed a fetus or two, but
evolutionary biologists know it's mainly there to attract potential sperm to create a fetus or two.
Unfortunately for those of you who are women, the sperms are delivered by creatures that are
annoying on their best days [I know this because I'm one of them, and I'm glad I don't have
to put up with me; that's my wife's problem]. I borrowed the chart above from the HealthCheck
Systems [a vendor of products for fitness and health] website, which cited the American Council on
Exercise as the source of the chart. The American Council on Exercise (ACE [www.acefitness.org])
is an organization involved in licensing fitness and exercise trainers, and the chart is from a
copy-righted book (ACE Lifestyle & Weight Management Consultant Manual) published by ACE. The
categories used do not match those in Nutrition texts, so I will give you my interpretation of how
“essential fat”, anything less than this is probably dangerously unhealthy
“athlete”, applies only to actual athletes and muscle builders,
and not to the casual ‘athlete’
“fitness”, is optimal for wellness
“acceptable”, is probably in the high end of ‘normal’
“obese”, is sufficiently over-weight to be a complicating factor in other medical conditions,
or possibly morbid obesity [a medical condition in which the excess weight causes other medical problems]
Current thinking suggests that even fat percentage is not a good indicator of risks associated with excessive weight. It is now being suggested that the storage location of body fat is more important than how much fat is being stored. [this reminds me that we did the same thing with fat intake… it's not so much the quantity of fat (or cholesterol) consumed, but the type of fat (Ω-3 versus Ω-9) that really matters].
All cultures that have been studied from an anthropological point of view have cultural expectations
of what members of each sex ought to look like, or their ‘ideal’ body shape. Note:
shape can be determined without knowing weight, BMI, body fat percentage, etc; you just give the
subject a quick glance to determine whether or not he/she is attractive. The only examples which are
“interesting” for this course are from Western Civilization, but there are several
sub-groups of this broad category. Obviously, there are separate cultural standards for men and for
women, but there are also minor differences in different regions [which roughly match the tribal
groups described by Julius Caesar in his Gallic Wars [De Bello Gallico], which begins
with the sentence fragment known to every one who took High School Latin, “Gallia est omnis
divisa in partes tres, …” [or in the translation made famous by an obscure comedian
from the dark ages, circa A.D.1957, “All Gaul is quartered into three halves”].
Beginning with the male perspective, or what women are supposed to look like. Out here in “the Colonies” (U.S., Canada, Australia & New Zealand), available females are on the slender side of of healthy (sizes small to medium, 5/6 to 7/8), with a clear ‘hour-glass’ shaped body, and a hint of muscle tone suggesting the ability to engage in occasional sports (tennis, volleyball, skiing, surfing). Although exaggerated hour glass figures are quite common in printed images that capture the male's attention, in settings where men are looking for dating partners the exaggerated hour glass figures get noticed across the room, but are not approached as often as the more slender females. Males have frequently been observed to behave as if they think that any female who matches their mental image of an attractive (or even reasonably close to attractive) female is available in spite of abundant signals from the female that she has absolutely no interest in him.
Turning to the female perspective [where I am far from an expert], or what men are supposed to look like. Based largely on feedback from former in-class Nutrition students [and comments by my wife and her friends about actors in particular movies], available males should have shoulders wider than their waist, and have clearly defined muscles (but not bulging muscles). They should have a rugged, outdoors look suggesting the ability to do occasional manual labor (mowing the lawn, shoveling snow, doing minor repairs around the house). Unlike the males, the females do not seem to spend much time looking at the males who do not look like the female's mental image of an attractive male, and even exhibit negative body language signals when it appears one of the imperfect specimens is about to approach her. The females have also been observed to emit giggling sounds when the imperfect males give up and retreat from the encounter. [I have a feeling, based on body language, that most of my former students would have skipped the above unless it was sufficiently entertaining, which it probably isn't].
So far, we have examined, and mostly rejected, numerous attempts to find some easily measured
value(s) that real people could use to determine when they have changed their body parameters enough
to improve their wellness. Our research-based thinking has now suggested that the location of fat
storage is important as a causal agent in risks associated with excess weight. The actual point of
the “naturalist's” narrative of Human behavior driven by cultural norms of attractiveness
was not to confirm that I am an alien who got here by flying saucer, but rather to suggest a
mechanism by which evolution could have improved wellness before the U.S. federal government decided
to become the nagging mother to the nation, if not to the entire World. If the early cavemen, a
million years or so ago had selected their mates on the basis of traits which are associated with a
lack of wellness, they should not have have much reproductive success; the population should have
gradually declined; and we should have gone extinct rather than taking over the World. Not only have
we taken over the World, we now act as if we think we can actually control it. At some point over
the last several thousand generations of our species, we began selecting mates on the basis of traits
associated with wellness, longevity, and high reproductive capabilities [in spite of having litters
of one, sometimes two; mice have litters of 6 to 8, and have had less success taking over the World
than we have]. The best evidence for how we did that is, since we select our mates on the basis of
how attractive they were, attractive must have something to do with wellness. But, we wondered, what
part of ‘attractive’ is important [Scientists tend to overthink things a lot]. For a hint
at the answer, we wander off to the weight management [diet] industry and learn that they have been
measuring circumferences of miscellaneous body parts for a long time, so they can tell their clients
how many inches they have lost as if that improves self esteem [although it actually does, but the
scientific types hope it's only the placebo effect]. There is no reason to believe that the effect
on self esteem is not real; dieters do exhibit a temporary increase in self esteem when they lose
inches instead of pounds. I am inclined to suspect that this is an intuitive understanding of
something the over-thinkers have only recently noticed.
There are three critical circumferences to be measured while assessing risk factors associated with a decline in wellness and life expectancy [and one of those may be unnecessary]: the chest, measured just below the breast (in females, basically the bra band size [as described on the Playtex/Bali/Hanes website]; in males, approximately at the lowest part of the pectoralis [pecs] muscles); the natural waist (measured at its narrowest point, or half way between the top of the hip bone [on the side] and the navel for those without a natural waist); and the hips (measured at their widest point. The lower half of the optimum range for these three measurements is as follows:
females: chest larger than waist; hips equal to or slightly larger than chest; the chest-waist-hip equals (34 to 36)-(27 to 29)-(37 to 39) (juniors sizes) or (34 to 36)-(27 to 29)-(37 to 39) (misses sizes) [measurements approximate based on U.S. Junior Size Chart and U.S. Misses Size Chart].
males: chest equal to or larger than waist; hips slightly larger than waist; the chest-waist-hip equals (36 to 38)-(34 to 36)-(35 to 37) [measurements approximate based on suit coat sizes, slacks sizes, and ‘no size data found’].
And the unhealthy:
females (low risk): waist larger than chest; hips slightly larger than waist
males (low risk): waist slightly larger than chest; hips slightly larger than chest.
females (high risk): waist larger than chest; waist larger than hips
males (high risk): waist considerably larger than chest; waist noticably larger that hips.
There is some good evidence that the chest measurement could be skipped, because the critical parameter is waist to hip ratio; but remember the effect on self esteem as a result of losing inches; the people will lose more off three measurements than they will off only two of the three. Besides, the three measurements seem to match the parameters describing the intuitive understanding of the attractive body shape. You can even tell people what the opposite sex expects as an ideal body, as long as you say it as if you knew what you're talking about [I don't have that problem - I have a PhD which gives me license to make up my facts as I need them for lectures; see the ‘optimal shape’ described above for an example of made-up facts (which are actually part of a hypothesis of mine, where the other word for hypothesis is “guess”)].
The most recent advice from ‘experts’is that you need only the waist measurement. Females should not exceed 35 inches (88 cm), and males should not exceed 40 inches (102 cm). Whether 3, 2, or 1 measurement is included in the assessment, the goal is to estimate internal fat deposits [in the gut] which are hypothesized to be the causal mechanism that allows excess weight to adversely impact life expectancies. Based on my hypothesis [untested] that the three measurement version (chest; waist; hip) is based on an intuitive assessment of health (estimated as attractiveness) developed over evolutionary history, I will predict that when the research has reached its logical end, we will have concluded that the three measurements are a better predictor of risk factors than the one (waist) or two (waist and hips) measurements. In the diet industry, you will find instances where miscellaneous other body parts are measured. The ones I have heard of include upper arms, wrists, ankles and thighs. As near as I can tell, these measurements were added so the clients of one diet company would lose more inches than clients of diet company “X” at least for advertising purposes. Pending scientific evidence to the contrary, I will continue to believe that they are meaningless in predicting life expectancy.
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© 2004-2010 TwoOldGuys
revised: 20 Aug 2010