Why obesity?

I choose Obesity in the United States for my blog because it seems to be a growing issue.  My parents have always talked about how they grew up seeing fewer cases of obesity then they do mow.  I am interested in what has happened that spurred this growth.  I also think that this will also allow me to look into other projects / studies to see what may have changed (examples:  growth of technology / portion distortion / instant gratification).