At the end of Fear of Food: A History of Why We Worry about What We Eat by Harvey Levenstein (2012), an historian at McMaster University, the author summarizes what he has learned:
During the course of writing this book, I have often been asked what lessons I personally draw from it. . . . The hubris of experts confidently telling us what to eat has often been well-nigh extraordinary. In 1921, for example, the consensus among the nation’s nutritional scientists was that they knew 90% of what there was to know about food and health.
Yeah. Two questions for an expert giving advice, especially apocalyptic advice (“You’ll die if you don’t . . . “): 1. What fraction of what there is to be known on your subject do you know? 2. May I quote you?
When I was a freshman in college, I went to hear a talk (off campus) about the chance of life elsewhere in the universe (or was it the galaxy?). The speaker multiplied a bunch of numbers together and came up with an estimate. “What’s the error in that estimate?” I asked. The speaker had no answer. He didn’t know. It’s essentially the same thing.