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Nutrition for Nursing Students, independent study

Optimal Body Weight

Weight is an important wellness issue for Nursing professionals, 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 in turn is an important Biological factor in driving behavior in all animal species]. 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 life expectancy.

Height - Weight as predictor of life expectancy

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 benefits are paid]). This led to medical professionals developing weight to height charts showing
      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 weigh our patients in pounds, and measure their 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, is compared to a chart to evaluate the patient's “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).

Reading BMI
weight status BMI
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 could have been diagnosed as ‘obese’ according to the BMI guidelines, yet his body fat percent was near [or below] the minimum acceptable value, so he was never diagnosed as obese [although he could have been diagnosed as ‘under weight’]. 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. The CDC also points out that 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 a 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]. ‘Best available 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 Health 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, 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%,) however, research has shown than the home scales are accurate [although they measure only lower body fat (thighs and hips), missing much of the critical abdomenal fat]. 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]. As for BMI, there are charts available showing desirable body fat for different groups of people:

% Body Fat guidelines
(from unreliable website)
female male
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 Human men are attracted to strangely located fat deposits [compared to other mammals] on women. Many textbooks try to pretend that 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 claims the chart came from the American Council on Exercise (ACE), an organization involved in licensing fitness and exercise trainers, but I was unable to find the chart on the the ACE website. The categories used do not match those in Nutrition texts, so I will give you my interpretation of how they compare:
      “essential fat”, anything less than this is probably clinically under-weight
      “athlete”, applies only to actual athletes and muscle builders, and not to casual ‘athletes’
      “fitness”, is optimal for wellness
      “acceptable”, is probably subclinically over-weight
      “obese”, is signs & symptoms of clinically over-weight, and potential obesity [remember, obese is a medical diagnosis of clinically over-weight]
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].

Cultural expectations for body shape

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 “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. [Now watch a Geico commercial where the ‘naturalist’ is narrating his observations of the spokes-geckgo; did you see any similarities to the above narratives? I have a feeling, based on body language, that most of my former students would have skipped the above unless it was considerd by them to be sufficiently entertaining, which it probably isn't].

Circumferences, meaningful and extraneous

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 [we 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 [lateral] and the navel for those without a natural waist); and the hips (measured at their widest point [usually at the head of the femur, but not always]. 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 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 (waist greater than about 31.5 [juniors or misses]).
      males (low risk): waist slightly larger than chest; hips slightly larger than chest (waist greater than about 39).
      females (high risk): waist larger than chest; waist larger than hips (waist greater than 35).
      males (high risk): waist considerably larger than chest; waist noticably larger that hips (waist greater than 40).
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 patient 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 patients 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 visceral adipose deposits 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.

Over-weight & Under-weight, classification of…


© 2004-2010 TwoOldGuys ™

revised: 16 Nov 2009