Emily (![[info]](http://l-stat.livejournal.com/img/userinfo.gif){kind=small} torrilin) wrote,@ 2007-10-11 19:58:00 |
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BMI and body image
Illustrated BMI Categories
It ain't perfect. But boy is it eye opening.
As I went through the images, I noticed a couple patterns. The BMI categories work fairly well on women in the 5' to 5'6" range. Outside that height range, the results seem to skew around wildly.
Women with breasts larger than a B cup *will* have at least an overweight BMI, no matter what their height. Women with a narrow waist and full hips are more likely to have an overweight BMI, no matter what their height. Women with visible collarbones will generally get classed as "normal". Women with starkly visible collarbones (ie, does not appear actively anorexic on camera) will get classed as "underweight".
So, we can see some obvious problems.
1. The bell curve of bras purchased centers around a B cup. Most bra fitting advice indicates that the more correct average size is C, possibly D.
2. Full hips tend to be associated with a larger pelvis. A larger pelvis tends to be associated with a larger birth canal. A larger birth canal is associated with easier childbirth. Biologically, full hips are a good thing.
3. Starkly visible collarbones are an indicator of anorexia (nervosa and otherwise). Rib count is also useful in a medical exam. 2-3 visible ribs are ok. Entire ribcage in relief is not usually ok, speaking as one who has been there. Details of spinal structure, pelvic structure or joint structure may also indicate anorexia. Biologically, a human with visible skeletal structure is at risk. We can run a very long time that way, but it is not the default state when there is an abundance of food.
So, BMI says any breast size over a B is unhealthy. If this is correct, it seems unlikely that women would have an average cup size in the C to D territory. It also seems unlikely that women who gain weight in their breasts would have consistently better health outcomes. Yet both of these are true... BMI says full hips are bad. This has serious structural implications for childbirth. If full hips really *were* bad, the pelvic structures that let a narrow hipped woman give birth easily would be common. There are structural defects that won't kill you (say, the malformed bone in my feet). A pelvic structural defect in a woman is often lethal (not just for her but for her genetic line). Until caesarean section was invented, it was lethal for her and her genetic line. BMI does not ring warning bells about disease. It treats visible bone structure as the normal state for an adult female, and very visible bone structure as a minor health problem.
What this tells me is that BMI is *not* an index. It's that same damn ectomorph height and weight chart, repackaged with a new name. You can generate the standard height and weight chart for adult women from some simple baselines.
60" of height = 100 lbs.
(num_inches_over_60 * 5) + 100 = ideal_weight
Go look at some of those images again. Notice anything about the heights and weights? Yeah. That. You don't get a "normal" BMI without matching the formula. (I am not male, so I do not have the male version of the equation memorized)
It doesn't matter how often doctors repeat that damn formula. It is biologically incorrect, since it encourages a body type that is not well suited to reproductive success. Doesn't matter if we *want* to reproduce or not, a body type that's potentially lethal should not be the baseline. Worse, it conceals lethal disease. Anorexia nervosa kills.
Another pattern that's hard to see in the images is also nasty. It's easiest to see the effects in the male images, tho with practice you can see it in some of the female ones as well. A muscular person, no matter what their gender, will have at least an overweight BMI. You do not get muscles without regular exercise. Regular exercise is necessary for good health. People who get regular exercise have better medical outcomes. Impact exercise is necessary to maintain bones. Aerobic exercise is necessary for the cardiovascular system. Ideally, people would do many sorts of exercise regularly, and thus would have good muscle structure, strong bones and a well developed cardiovascular system. Because BMI penalizes most people for having muscle mass, it discourages healthy behavior.
So. The formula has serious biological problems, and serious long term health implications. Why are we using it again?
Illustrated BMI Categories
It ain't perfect. But boy is it eye opening.
As I went through the images, I noticed a couple patterns. The BMI categories work fairly well on women in the 5' to 5'6" range. Outside that height range, the results seem to skew around wildly.
Women with breasts larger than a B cup *will* have at least an overweight BMI, no matter what their height. Women with a narrow waist and full hips are more likely to have an overweight BMI, no matter what their height. Women with visible collarbones will generally get classed as "normal". Women with starkly visible collarbones (ie, does not appear actively anorexic on camera) will get classed as "underweight".
So, we can see some obvious problems.
1. The bell curve of bras purchased centers around a B cup. Most bra fitting advice indicates that the more correct average size is C, possibly D.
2. Full hips tend to be associated with a larger pelvis. A larger pelvis tends to be associated with a larger birth canal. A larger birth canal is associated with easier childbirth. Biologically, full hips are a good thing.
3. Starkly visible collarbones are an indicator of anorexia (nervosa and otherwise). Rib count is also useful in a medical exam. 2-3 visible ribs are ok. Entire ribcage in relief is not usually ok, speaking as one who has been there. Details of spinal structure, pelvic structure or joint structure may also indicate anorexia. Biologically, a human with visible skeletal structure is at risk. We can run a very long time that way, but it is not the default state when there is an abundance of food.
So, BMI says any breast size over a B is unhealthy. If this is correct, it seems unlikely that women would have an average cup size in the C to D territory. It also seems unlikely that women who gain weight in their breasts would have consistently better health outcomes. Yet both of these are true... BMI says full hips are bad. This has serious structural implications for childbirth. If full hips really *were* bad, the pelvic structures that let a narrow hipped woman give birth easily would be common. There are structural defects that won't kill you (say, the malformed bone in my feet). A pelvic structural defect in a woman is often lethal (not just for her but for her genetic line). Until caesarean section was invented, it was lethal for her and her genetic line. BMI does not ring warning bells about disease. It treats visible bone structure as the normal state for an adult female, and very visible bone structure as a minor health problem.
What this tells me is that BMI is *not* an index. It's that same damn ectomorph height and weight chart, repackaged with a new name. You can generate the standard height and weight chart for adult women from some simple baselines.
60" of height = 100 lbs.
(num_inches_over_60 * 5) + 100 = ideal_weight
Go look at some of those images again. Notice anything about the heights and weights? Yeah. That. You don't get a "normal" BMI without matching the formula. (I am not male, so I do not have the male version of the equation memorized)
It doesn't matter how often doctors repeat that damn formula. It is biologically incorrect, since it encourages a body type that is not well suited to reproductive success. Doesn't matter if we *want* to reproduce or not, a body type that's potentially lethal should not be the baseline. Worse, it conceals lethal disease. Anorexia nervosa kills.
Another pattern that's hard to see in the images is also nasty. It's easiest to see the effects in the male images, tho with practice you can see it in some of the female ones as well. A muscular person, no matter what their gender, will have at least an overweight BMI. You do not get muscles without regular exercise. Regular exercise is necessary for good health. People who get regular exercise have better medical outcomes. Impact exercise is necessary to maintain bones. Aerobic exercise is necessary for the cardiovascular system. Ideally, people would do many sorts of exercise regularly, and thus would have good muscle structure, strong bones and a well developed cardiovascular system. Because BMI penalizes most people for having muscle mass, it discourages healthy behavior.
So. The formula has serious biological problems, and serious long term health implications. Why are we using it again?
