The arguments over diet go way back, said Dr. Rudolph L. Leibel, an obesity researcher at Columbia University's College of Physicians and Surgeons. "They are in fact an echo of the discredited scientific notion of vitalism," he said of the idea that living things are not governed by the laws of chemistry and physics.

Although vitalism was disproved 200 years ago, he said, it is behind the fevered search for a magic way of eating that can override the rigid scientific formula: calories in minus calories out govern weight gain and weight loss. Discovering a diet, Dr. Leibel says, "is almost like a revelation."

The 19th century saw, for example, the emergence of the Rev. Sylvester Graham, a promoter of vegetarianism for whom the Graham cracker was named. Graham insisted that people could rise above hunger and cravings if they would just stop being slaves to their stomachs. His followers favored fresh fruits and vegetables, grown without fertilizers, and made bran bread. They established "physiological boardinghouses" where people could live the Graham way. Skeptics were scathing. Dinner at a Graham house, they said, featured delicacies like "straggling radishes," "a soggy bunch of asparagus" and "corpses of potatoes," washed down with "a tumbler of cold water."