Three Reasons Why The 40% Drop in Infant Obesity Means Less Than Some May Think

EscalatorEven the casual reader will not have escaped the recent exuberant media reports that, when it comes to childhood obesity rates in the US, the worst may be over.

There was certainly also no shortage of folks claiming credit for this “success”.

Interestingly enough, this enthusiasm was not shared by Cynthia Ogden and colleagues in their JAMA paper on the Prevalence of Childhood and Adult Obesity in the United States, 2011-2012, came to the following conclusion:

“Overall, there have been no significant changes in obesity prevalence in youth or adults between 2003-2004 and 2011-2012. Obesity prevalence remains high and thus it is important to continue surveillance.”

Indeed, the overhyped media report was based on an isolated subgroup analysis in infants and toddlers (2 to 5-year olds), where obesity rates dropped from from 13.9% to 8.4% a difference that barely scraped statistical significance (P = .03).

No changes or increases were seen in every other subgroup with rates as high as 16.9% in 2- to 19-year-olds and 34.9% in all adults 20 years or older. In women aged 60 years and older, obesity rates actually increased from 31.5% to 38.1% (P = .006).

So here are my three reasons why these results of the putative drop in toddler obesity mean almost nothing.

1) This is a subgroup analysis of a subgroup – anyone with any knowledge of statistics should treat any such results with extreme caution (as clearly the authors themselves do).

2) We are talking infants and toddlers – this is not the group where obesity powerfully tracks into adulthood (or even into adolescence).

3) Infants and toddler don’t generally make “independent” behavioural decisions (although parents of young kids will agree that this is not at all what life with toddlers feels like). Thus, it is entirely unclear what “behaviours” of these toddlers will carry over as they get older and become more independent.

If the findings are at all true and representative, then at best, they suggest that parents of very young kids may be “getting the message”, though exactly what that “message” is and what exactly the parents are doing about it is quite unclear to me.

On a happier note, overall obesity rates appear to have stabilised at least in the US. Perhaps we have now reached that point in the epidemic, where everyone who can be obese is obese.

Edmonton, AB

ResearchBlogging.orgOgden CL, Carroll MD, Kit BK, & Flegal KM (2014). Prevalence of childhood and adult obesity in the United States, 2011-2012. JAMA : the journal of the American Medical Association, 311 (8), 806-14 PMID: 24570244