Zanthe Taylor M.F.A.

A Million Meals

The Perils of BMI Screening

When public health becomes public hazard

Posted Jan 28, 2013

We live in a time of aggressive self-improvement. We are constantly told that if we can grab the reins, wrestle for control over our lives, we can solve all (or most of) our problems. Moreover, we hold self-evident the maxim that Knowledge is Power: the more information we have, the better off we will be. From exhortations to “eat mindfully” to continuing scientific exploration of the human body and mind, science and the media work hand-in-hand to popularize the notion that knowing more is the essential first step towards curing all that ails us—and perhaps the second or third step as well.  Yet there are many efforts to harness knowledge to the service of improving our health and well-being that may seem beneficial but actually have negative and even destructive results. The currently popular theory of mindfulness does not always lead to better decision-making.

One telling example is the decision of some states to measure and report public school students’ BMIs (Body Mass Index) as an attempt to curb childhood obesity. Twenty states require BMI or similar screening, and nine recommend either BMI screening or a formal fitness assessment that includes a body composition component. This decision may appear as innocuous as the principle of “healthy eating,” but it can be equally damaging.

The BMI is an extremely fuzzy number masquerading as a hard scientific fact. The calculation, dividing one’s weight by the square of one’s height, was devised in the 1830s; although it is popularly explained as a measurement of body fat, it actually doesn’t measure body fat. The calculation itself has recently come under attack for its imprecision, overestimating the BMI for taller people and underestimating that of shorter people. Not to mention that however it’s calculated, the number is only useful after some expert source informs us whether our BMI falls into the category of underweight, healthy/normal, overweight or obese. Who determines these ranges? And do they shift or have they been fixed since the mid-nineteenth century? These very basic questions, requiring some research to answer, ought to point out to you how imprecise and subjective a number the BMI is, and how foolish it is to place our faith in it as an indicator of our health. Even the experts will tell you, albeit only in the fine print, that BMI is useful as a large-scale analytical tool rather than a measure of individual health. It is inappropriate for the latter task, and yet we are subjected to it constantly as a measure of our individual health.

Of course, we are, as adults, at liberty to calculate and fixate on whatever numbers we choose. Though I don’t envy people who weigh themselves daily (or more) and calculate their well-being based on the loss of gain of a few pounds, it’s not in my purview to tell them they have to stop. But it’s quite a different thing when a school or local government is requiring these calculations and then either using them or passing them on to parents—or, in the most egregious cases, to the students themselves. How much do parents understand about the utility or limitations of the BMI, and what are the consequences of their receiving this number from their child’s school?

Some parents, certainly, will do nothing. But others will, or will have to face children who have been told their “number.” It’s easy to feel pressured by a BMI that falls outside the variously described “healthy” or “normal” range into making decisions that may not be appropriate or truly healthy for your child. How much information do schools provide parents with about the significance of the number? Anecdotally, no one I corresponded or spoke with who received a BMI report from their child’s school could recall any accompanying context or guidance on what they were supposed to do with that information. Children with a high BMI in some states were sent a follow-up letter, which contained information about how to live a so-called “healthier lifestyle.” But discharging the responsibility onto families to alter things which they may be either powerless or disinclined to change is an egregious example of passing the buck, regardless of whether one even accepts the validity of the BMI as a useful measure in that context.

Finally, do schools examine family backgrounds to see whether there may be underlying disordered eating behavior in the home, or provide parents with sufficient resources to address the perceived problem? The BMI is a blunt tool being used to tackle an extremely nuanced and complicated problem. It doesn’t take much research to discover how close below the surface lie misgivings and problems. The CDC’s online pamphlet on school BMI programs uses anodyne, scientific language to outline the benefits of “surveillance” and information gathering. Yet even here, reading further, we find warnings that these programs can be harmful to families and children. Results may be stigmatizing, the report mentions, though it falls back on the less controversial stand that “more research is needed to assess the validity of these concerns.” The authors conclude:

Schools that initiate BMI measurement programs should have in place a safe and supportive environment for students of all body sizes and a comprehensive set of science-based strategies to promote physical activity and healthy eating. In addition, BMI screening programs should ensure that parents receive a clear and respectful explanation of the BMI results and appropriate follow-up actions; and that resources are available for safe and effective follow-up. 

Yet what are these “science-based strategies” that magically ensure better health? If they were readily available wouldn’t we already be applying them? And it’s one thing to say schools “should” do this and that, but quite another to examine whether they do.      

Talking to parents whose children have been part of BMI screening or surveillance programs reveals what confusion the results provide. One New York City family received a “fitnessgram” from their daughter’s school that put her child's BMI in the zero perentile. Another mother could barely bring herself to tell me what a painful, traumatizing experience the process had been for her middle-school daughter and her friends. A parent who is also a teacher wrote that she recalled her own adolescent transition from slender child to womanly adolescent as well as the attendant discomfort and shame; she has watched her students undergo these transitions with empathy and would, she says, “fight this kind of ‘educational activity’ tooth and nail in any school where I taught; the benefits would not outweigh the harm when done in this environment.”

Programs such as this one, ostensibly harnessing information to action, are in reality so confusing to families that they run the real risk of creating problems that may not have existed in the first place. The Eating Disorders Coalition, a group working to promote federal action on eating disorders as a public health issue, is strongly opposed to BMI reporting in schools because of the strong possibility that it will lead to harmful behaviors. The BMI of a pre-adolescent child measures a moment in time, while obsessive thinking and eating disorders can last a lifetime. While I am an enthusiastic proponent of public health initiatives in general (even some controversial ones like Bloomberg's soda tax), I do see BMI testing—even in a doctor’s office—as the tip of a particularly treacherous iceberg. Public health policy too often treats weight as a quasi-mathemetical issue that can be separated from essential factors such as mental health, family or community dynamics, and government policy. Numbers such as the BMI provide fuzzy or false information, which is then used to questionable or even disastrous effect, all under the false gloss of scientific clarity. More information doesn't always lead to true knowledge, and we should be more skeptical of claims that it does, especially in the arenas of health and weight.

What I cooked this week: