We tend to think of health food as a modern invention, but humans have made the connection between food and well-being at least since the beginning of written history—although it's always been as much a matter of educated guesswork as solid science.
Ancient Greeks believed that good health was dependent on maintaining the balance of the body's four "humors"—black bile, yellow bile, phlegm and blood—and that modifications in diet could restore balance if levels got out of whack. Hippocrates, Plutarch and other thinkers wrote books on the relationship between food and health, including Galen's On the Power of Foods, a title that sounds like it could have been written last year.