It's cheaper to go to the grovery store and buy the same raw potatos and oil that would go into the potato chips than buying the potato chips themselves.
Also, fine, 80/20 beef is cheaper than lean beef, but then the products made with that 80/20 beef are more expensive than their ingredients (not always, but frequently.)
This correlation hardly proves your point.
For example, there are simply no grocery stores in a lot of poor urban neighborhoods where one can buy produce, which forces people to buy and consume processed foods.
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