(Since you happened to bring that up)
I’ve thought for a while that that advice needs updating, if he hasn’t done so already.
IMO it’s fine advice for older people: Michael Pollan himself is currently 67 years old, so his grandmother might be from an age where that advice would hold.
But take someone who is currently 18-20 years old, say, and their grandmother could be, say, in her 50s—easily young enough to have grown up in the days of artificial-everything food 
