A good place to start is to read Michael Pollan's Omnivore's Dilemma[1]. I was amazed at how much of our current food originates as corn. Corn is good at fattening cattle in record time, and seems to be having the same effect on humans who eat its derivatives.

[1] https://www.goodreads.com/book/show/3109.The_Omnivore_s_Dile...