Mr. Pollan talks about his food rules on NPR program "Earth Eats." Here's a snippet:
I do know some vegetarians and vegans who don't really pay attention to the origins of their food (e.g. Oreos). For me, the source of my food is of the utmost importance and I always read labels, remain loyal to ecologically friendly, small food producers and always support local farmers and/or grow my own food. The reason I'm vegan: I don't really like meat and don't agree with how it's produced on mass scale. I may be slapped by the vegan police for writing this, but, if my family or friends want free-range eggs or locally raised meats, I'd be happy to buy it for them if I know where it comes from. This doesn't mean I'm going to eat it, but it's the first step in helping them to start a new ethical eating regime.
Even if you're vegetarian, be a discriminating eater and ask questions! Not just the obvious ones about the existence of animal by-products, but how and where you food is grown. It's great if we can convert some of our friends to meat-free lifestyles, but it can't be the end-all if we want to create a dialogue on and enact change to our food system.