Afterward, I grab Gardner as he is heading for his vegan lunch. He explains that what we know about nutrition so far comes from big studies like Willett's and small targeted trials like his. Willett watches thousands of people, year after year, to see who dies and who lives. But Willett can't prove that it was, say, the whole grains in their diet that protected them — so Gardner runs randomized trials to isolate one element and try to determine cause and effect. Here's what he finds instead: "One little thing at a time never makes a difference."

not much of a surprise.