The cause could be that people with poor SES still have worse nutrition (lack of some nutrients) and thus the urge to consume.
(I mean, in addition to the urge caused by malnutrition in childhood.)
What are the most common kinds of bluff food and do you think anything could be done about it?
What we do know is that animals and humans have a natural ability to balance their diet (by developing seemingly random cravings?) and that this ability is increasingly breaking down in "western civilisation". It is a small jump from that to the idea that market driven "yummy engineering" could be the perfect setup to find the fault lines in our diet balancing instincts.
http://archinte.jamanetwork.com/article.aspx?articleid=57792...
http://www.tandfonline.com/doi/abs/10.1080/08880010590896486
http://www.samj.org.za/index.php/samj/article/viewFile/358/3...
http://www.sciencedirect.com/science/article/pii/00029343829...