In the fall of 1957, a Minnesota doctor named Ancel Keys traveled from Naples to the southern Italian town of Nicotera. The road was long and dusty, winding for hours into the mountainous toe of the Italian boot. But the trip was worth it. Keys, a physiologist who had spent World War II developing combat food rations, was searching for the answer to one of the great questions of healthy living: Why did heart attacks plague some groups of people (say, Minnesota businessmen) while leaving others (southern Italian farmers, for instance) nearly untouched?
Keys spent his stay in Nicotera measuring body-fat...