Childhood obesity and a brief note on the BMI


Blame the food? Blame the child? Blame the parents? Work to find a solution?

Each year the latest reading on childhood obesity is released. The information is collected in the NHANES survey, published in a prestigious journal and interpreted by health reporters in media across the country and beyond. Last year gave us good news. The childhood obesity level reported in 2017 was lower than that reported in 2016. Were we finally making a dent in the epidemic? This year the level has gone back up, and the problem looms even larger. NPR reports that the most disturbing trend is the increase in obesity for 2-5 year old children.

In going directly to the article published in Pediatrics, the news is dire. The authors have used some different ways of recalculating obesity rates, so it is difficult to compare their results and conclusions with those from previous reports. From their calculations, however, we see no evidence for a leveling off or decrease in childhood obesity in recent years. Problems with past reports have included the up-and-down nature of the yearly information. Through a series of statistical techniques, the authors have smoothed out the data to show the clear trend that childhood obesity is still increasing. Part of this data smoothing involves averaging the results over two-year periods rather than reporting it from single years. The scientists who wrote the Pediatrics article caution readers to interpret the results carefully, because

  • individual children are not tracked from year to year,
  • the trends for subgroups (age, ethnicity etc.) are not as reliable as the overall picture, and
  • it is not clear that obesity across ethnic/racial subgroups represents similar health risks.

The NPR story and other reports in the media have tended to ignore these precautions.

My big issue with these news stories is that they focus in on a single year rather than to try to look at the big picture. Although Yoni Freedhoff and I frequently disagree with each other, I concur with his plea to the media to “Please stop!” Collecting this information on a yearly basis is important, but interpretation of the reports in context is necessary. Yearly news stories are not helpful. A report for any single year is just a snapshot in time, and a blurred one at that. In viewing such data, we need at least three points in a row going in the same direction to draw any conclusions about a meaningful trend. The Pediatrics article has smoothed out the data to show a clear trend. My question becomes

Is this a more useful way of interpreting the data or is it a manipulation of the data to confirm a preconceived conclusion?

All that I can conclude from the annual reports of the past several years is that (1) our children are too fat, (2) there are many solutions proposed to combat childhood obesity, many of them contradictory, and (3) no national program is currently in place to help solve the problem.  The closest thing to a national program to fight childhood obesity, Let’s Move, died in November, 2016. A major problem with science journalism in general and news stories on food and nutrition in particular is that too many journalists rely on oversimplified conclusions from single studies. A research article published in a scientific journal is like a piece of a jigsaw puzzle and not a completed picture. News stories tend to present the findings of these single studies as the final chapter in the search for truth that solves the problem once and for all.

When I am trying to learn about a topic outside my area of expertise, I look for review articles that provide a broader perspective and not the most recent newsworthy study. Such reviews put contradictory results from different research labs into a more rational context. I am convinced that where science gets the reputation of changing its mind—what was bad for us last year is good for us this year—is the sensational reporting of too many single studies. Nate Silver in the Signal and the Noise suggests that science never gets us to absolute truth. Rather, the body of scientific research in any one area helps us discard false information and gets us closer to the truth.

A brief note on the BMI

The Body Mass Index, or BMI, is the tool used by our society to assess obesity and has become the overall index for health of an American. As I pointed out last week on this site, the BMI has flaws as the relationship between BMI and body-fat composition is not linear. There are many other problems with using the BMI as the primary measure of a healthy weight and health in general. The index seems to give a reasonable estimate of over/underweight status of a general population but not necessarily for an individual person. It is a simple measure that gives a clear numerical answer, but what works for one ethnicity does not necessarily work for another ethnicity. The same reservations also relate to the elderly like me or children in general. BMI is an imperfect measure of weight status and weight, in and of itself, is an inappropriate guide to health.

Childhood obesity is defined as “a BMI at or above the 95th percentile for children and teens of the same age and sex.” According to an author of the Pediatrics study an historical cohort averaged across children measured and weighed from the 1960s to 1980s are used as the reference points. By the way, Yoni Freedhoff, a M.D. specializing in obesity and co-owner of the Bariatric Medical Institute, suggests that it is never a good idea for a parent to weigh their child. One further note; it strikes me as ironic that it was the advocacy in the 1970s of Ancel Keys that led to the establishment of the BMI as the measurement of weight status in the United States. Yes, that is the same Ancel Keys who is vilified by food evangelists everywhere as the person who made us focus on fat, specifically saturated fat, in the diet allowing Big Food to poison us with too much sugar. See The Case Against SugarOf course, the issue is much more complicated than what is being reported in the media.

 Next week: Harvest boxes and food stamps

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