Abstract
In late February, an article by Ogden and colleagues was published in The Journal of the American Medical Association with the seemingly bland title, “Prevalence of childhood and adult obesity in the United States, 2011–2012.” 1 Packaged within a morass of data pertaining to all age groups was a downward deflection in the obesity rate in children ages 2–5 years. Somehow, this yielded the following headline in The New York Times: “Obesity rate for young children plummets 43% in a decade.” 2
If, indeed, obesity rates in young children had plummeted over the past decade, it would be cause for celebration in the editorial offices of this journal with champagne all around. But, alas, the champagne bottles remain corked and unperturbed where they lie. Why?
The first reality check is the study conclusion in the researchers' own words: “Overall, there have been no significant changes in obesity prevalence in youth or adults between 2003–2004 and 2011–2012.” 1 My friend and colleague, David Allison, PhD, at the University of Alabama, publishes a weekly overview of important studies related to obesity, including a feature on discrepancies between what headlines say and what the corresponding studies actually say. This one topped that list.
What the investigators actually reported, tracking data over a decade, is, as noted, no overall change in the population rate of obesity. In the survey sample of just over 9000 people, representing the population of 300 million, obesity rates were stable in most age groups, including infants under the age of 2 years. Rates rose significantly in women over age 60 and fell significantly—although barely so (p=0.03)—in children between the ages of 2 and 5 years. 1
That, then, was the tale that shook the dog in late February, spawning a deluge of hyperbolic headlines: in 871 children between the ages of 2 and 5 years, obesity prevalence declined whereas it remained steady or rose in all other age groups, including children younger still.
Even so, a decline of 43% as reported in The New York Times, and elsewhere, still seems fairly impressive. But, what does 43% mean? The 43% decline reported was not an absolute percentage, but a relative percentage. This audience doubtless appreciates the difference, but an illustration can do no harm. Imagine a population of exactly 100 children, ages 2–5 years; and imagine that 60 of them are obese. Compare this group to another group the same age a decade later in which only 17 of the kids are obese. The absolute difference in the obesity prevalence here would be 43%.
Now, imagine instead that in the original group, a decade ago, approximately 15 of the kids were obese; and currently, in a comparable group, approximately 9 of the kids are obese. The absolute decline in obesity prevalence is, obviously, only 6% (i.e., 15%−9%). However, what about the relative decline in obesity? That would be 40%. The formula for it is: ([15%−9%]/15%)=40%. The 6% decline is 40% of the baseline number. That is the difference between absolute and relative percentages. Absolute percentages are out of 100, which is what most of us expect. Relative percentages are out of the starting number, whatever that happens to be. On a relative scale, a drop from 2 people per hundred having X to 1 person per hundred having X is not 1%; it is 50%. That would still be true if the drop were from 2 per million to 1 per million. Relative percentages are often reported in the medical literature, and routinely reported in the popular press, for the most obvious of reasons: They tend to sound a whole lot more dramatic than the much smaller, absolute numbers.
What were the actual, absolute numbers in this case? Obesity rates in the 2- to 5-year-old age group fell from 13.9% to 8.4%, an absolute difference of 5.5%. I trust you can see why the relative change made the headlines. An announcement that “overall obesity rates are unchanged over the past decade, with some increases seen, and a possibly encouraging decline of roughly 5.5% in children 2 to 5” is accurate, and about as dull as dishwater. It does not well suit the media mantra: afflict the comfortable, comfort the afflicted. 3 We have long been afflicted with bad news about the obesity epidemic; it was, apparently, time for a 43% dose of comfort.
In setting the record straight, I do not want to go too far. A whole lot of attention has been directed at the problem of childhood obesity over the past decade, including the signature efforts of the First Lady, as well as the establishment of this very journal. We recently saw study data indicating that obesity by age 5 years is a potent predictor of lifelong weight struggles to follow, 4 thereby implying the converse: weight control before age 5 years could confer lifelong benefit. That being the case, any decline in obesity prevalence in this age group is of particular importance.
The new study offers some potentially quite encouraging and important news. However, I say “potentially” advisedly. First, the “good” news here is that nearly 1 in 10 of our kids under age 5 years is obese. That such a statistic is cause for celebration says more about how bad we let things get than about how good they now are.
Second, looking at the detailed data tables in the article, I see that obesity rates did not fall steadily over the past decade, even in the one group of putative winners, children age 2–5 years; they fell, then rose, then fell again. 1 This suggests that we may not yet have a reliable trend established, and the most recent numbers are just part of a fluctuating baseline. More time will tell. I am also concerned that the prevalence of excess weight for length among infants and toddlers under age 2 years has not trended down. It, too, has bopped around and, overall, is statistically unchanged over the past decade. This, of course, is the next cohort of 2 to 5 year olds, so if their propensity for obesity is not falling, it is a portent of bad things to come. To see real promise in this study, as we all would like to do, requires an embrace of optimism, as well as a glass half full firmly grasped.
Some years ago, I established my nonprofit organization, Turn the Tide Foundation. 5 As the name implies, our mission was, and is, to contribute all we can to efforts to contain and reverse the ever-worsening trends in obesity and related chronic diseases in adults and children alike. Over the years since, we have developed, tested, and disseminated a number of helpful programs free of charge, some of which now have considerable traction all around the world. 6
The name I chose for the Foundation is closely related to how I view the origins of the obesity and chronic disease pandemics we are pledged to combat. Rather than seeing obesity as a disease, which implies something wrong with the bodies it affects, I see it as much like drowning—the consequence of bodies interacting with an environment for which they are ill suited. 7 Our problem, at its origins, is a vast, obesigenic flood. 8
With that metaphor reflecting my view of the problem, it naturally invites another as the corresponding solution: a levee. When you want to contain and reverse menacing floodwaters, you build something like a levee. In doing so, you know that no one sandbag, however “good,” will do what the whole levee can do. It will take a whole lot of sandbags to top the height of the floodwaters and turn the tide. Similarly, no one thing will fix the scourges of modern epidemiology; it will take all the right programs in all the right settings to put opportunities for health reliably and accessibly back on dry ground.
We should all recall that floodwaters crest not when the snow stops melting and precipitation stops falling, but quite some time after. Globally, the tempest of obesity in adults and children alike continues unabated with both the prevalence and price, in human and monetary terms, rising for as far ahead as we can see. 9
Here in the United States, we are, at best, still producing a sizable cohort of obese 5 year olds, despite our considerable efforts, and the even larger cohort of obese 5 year olds from several years back is just now entering the age of risk for serious metabolic complications. Here, too, the most severe consequences of rampant childhood obesity are yet to come. Here, too, the floodwaters have yet to crest. The lack of change in children under age 2 years looks a bit like storm clouds on the horizon to me. We must, therefore, remain committed to stacking sandbags, and raising the levee, for the foreseeable future. We should, if anything, redouble those efforts.
The good news about childhood obesity trends is not nearly good enough to warrant champagne or confetti. The tide has not yet turned. But, there is some good news just the same, suggesting that maybe—just maybe—the rain is slowing. Though not inclined to raise a glass, I am inclined to lower my umbrella and enjoy a bit of sunshine in what has, for far too long, been a very overcast sky.