I would say that generally speaking the media's influence is not a good thing. To be sure there are some exceptions, like Jamie Oliver and his food revolution movement and some good documentaries on food and the importance of eating well or studies on how food is produced. However, there are so much more on unhealthy choices through the media. There is a reason for this.
When it comes to the media, you have to sell airtime to advertisers. In the end, it is all a business. There is almost a conflict of interest, because companies that buy air time for commercials owns the media in a sense. So, when MacDonald's, Burger King, and a whole bunch of other vendors that produce unhealthy foods bombards the airwaves, television, and internet with their products, it creates for a society that is saturated with unhealthy food choices. In light of this, the media does not help much when it comes to healthy food choices.