>I'm not sure we have any clear sense of what, in out hyper-efficient industrial food economy does this. Come to think of it, we don't even know it's the food -- could be something else environmental.

Food or environmental, but in a larger sense, it's likely to be some additives, is my uneducated gut-feel (pun unintended) guess. Here by additives, I don't mean only ones in food, but also fertilizers, pesticides, other synthetic chemicals, and agricultural and industrial effluents.