But you and your body aren't the only ones with a stake in this game. Your doctor has opinions about what you should eat. So does your family. And so too do the food purists who lately seem to be everywhere, insisting that everything that crosses your lips be raised and harvested and brought to market in just the right way. If you find this tiresome — even intrusive — you're not alone. "It's food, man. It's identity," says James McWilliams, a professor of environmental history at Texas State University. "We encourage people to eat sensibly and virtuously, and then we set this incredibly high bar for how they do it." (See whether you should buy organic or conventional food.)