Kind of a tangent but Michael Pollan's books always open my eyes about these topics. In particular for this subject https://en.m.wikipedia.org/wiki/The_Omnivore%27s_Dilemma gives a good overview of why fast food (and all highly processed food) are so much cheaper than eating whole food. In the process you start to understand the role corn has on it and why it's the biggest crop of grain in the world.