TV Viewing and Childhood Obesity – Less Related Than Expected?Friday, April 6, 2012
Never mind that it is usually impossible to infer causality from observational studies or, even if significant associations are noted, to predict what may or may not happen, when one of the variables is targeted (as in an intervention). It is also worth noting that many common stereotypic assumptions we make about what may or may not be driving the obesity epidemic continue to be challenged by the actual data on these issues.
A good example of this state of affairs is the recent paper by Valerie Carson (a former CON Bootcamper) and Ian Janssen (an enthusiastic Bootcamp faculty member), from Queens University, Kingston, Ontario, published in Pediatric Obesity on the relationship between TV viewing, snacking, and childhood obesity.
While we are all familiar with the ‘stereotypical’ pictures of the fat kid with a bowl of chips with eyes glued to the TV set, suggesting that fat kids are fat because they do little else than watch TV and eating chips (forgetting that skinny kids may do exactly the same), this paper certainly does not easily support this notion.
The study looked at the self-reported snacking and TV viewing habits in relationship to BMI in almost 16,000 youth in grades 6–10 who participated in the Canadian 2009/2010 Health Behaviour in School-Aged Children Survey (HBSC).
Participants reported the frequency of snacking while watching television and the frequency of eating junk food (sweets, soft drinks, baked goods, French fries, potato chips). Total hours per week of television were also calculated.
Although there was certainly a modest positive relationship between television viewing and BMI, this did not seem to be mediated by television snacking or junk food consumption. If anything, the relationship between the latter appeared to be slightly negative.
While there may well be all kinds of methodological and potential confounders of why these findings do not support the ‘hypothesis’ (increased snacking of junk food while watching TV is an important driver of childhood obesity), it certainly appears that this effect, even if it exists, is probably far less powerful than most of us would expect.
Sure, self-reported data (not just in kids) should always be taken with a grain (or teaspoon?) of salt, but then again, one would need to hypothesize that skinny kids are perhaps more ‘truthful’ about reporting their behaviours, something for which there is even less evidence. And yes, the study does not tell us about general snacking or junk food consumption outside of TV viewing but other studies have shown that the commonly held notion that fat kids apparently live on a staple of unhealthy junk foods and soda pop while skinny kids are more likely to be weight-conscious organic vegans, is not exactly true either.
The key learning for me from such studies is merely that much of what we so often assume as the ‘key drivers’ of obesity do not appear to be all that ‘key’, when we look at the actual studies published on these issues (regular readers may recall the results of the Canadian Measurements Survey, which did failed to show that fat kids were any less active than skinny kids).
Obviously, such studies also almost never look at the ‘whys’ (rather than the ‘whats’), as this would be a whole different line of research.
Perhaps, when data does not support the stereotype, it is time to question the stereotype rather than the data.
Carson V, & Janssen I (2012). The mediating effects of dietary habits on the relationship between television viewing and body mass index among youth. Pediatric obesity PMID: 22461393