What causes obesity?

Here is a Scientific American article about this.

I found this paragraph interesting:
“Bickham says three theories have been floated for the link between screen time and obesity: food advertising, unconscious eating and displacement—that is, the idea that the media use replaces physical activity. His team’s findings lent more support to the first two variables and less to the third. They found video games and computer use had no impact on BMI (body mass index). Television did, but only if it was the main event. Background TV, for example, didn’t matter.”