Ok, maybe not so shocking.
In my talks on childhood obesity I'll always point out that the simple act of sitting on a sofa doesn't in and of itself cause weight gain and on my blog I'll also regularly point out that the rise in childhood obesity isn't a consequence of a lack of physical activity, but rather an increase in food. Putting those two together I've always presumed that TV watching was symptomatic of a less healthy lifestyle that included more calories than the lifestyles of kids who didn't watch much TV.
Well guess what? Maybe I was right. A fascinating study was recently published in the journal Obesity that specifically sought to answer what it is about watching TV that leads kids to gain weight. The study looked at the TV viewing habits, lifestyles and weights of 2,374 Greek children between the ages of 1 and 5.
Those kids watching the most TV were indeed the heaviest and this relationship persisted even after controlling for potential confounders like physical activity. What this means is that kids who exercised and watched lots of TV still had the same rates of obesity as the kids who didn't exercise and watched lots of TV.
So what was the cause? The researchers studied many different variables but at the end it came down to the simple fact that the kids who watched the most TV consumed the most calories.
Now exactly what, when and why they're eating more isn't yet clear. Are they eating more junk because they see more commercials for junk? Do they sit there with a bag of chips in their laps (the researchers think indeed, it's food consuming while watching TV that makes the difference), or are they eating more in the hours they're not watching TV? The stuff for future research.
Bottom line? Once again it seems it's about intake and not output.
Manios, Y., Kourlaba, G., Kondaki, K., Grammatikaki, E., Anastasiadou, A., & Roma-Giannikou, E. (2009). Obesity and Television Watching in Preschoolers in Greece: The GENESIS Study Obesity, 17 (11), 2047-2053 DOI: 10.1038/oby.2009.50