OAKLAND, Calif. DR. PRESTON MARING was striding along a hospital corridor at double speed on a recent Friday morning, his tall frame, white hair and frequent gesticulations prompting waves of greetings from colleagues, who also took care to sidestep his forward momentum. His destination was the weekly farmers’ market he started in 2003, just outside the front door at the Kaiser Permanente medical center here. “Since it’s mine, I made the rules — all organic,” he said as he skimmed by a line of stalls where fresh fruits and vegetables are sold to hospital workers, passers-by and even, he said, those bringing patients to the emergency room. Dr. Maring, 64, a gynecologist and obstetrician with three decades as a surgeon, is well known as a former physician in chief at the hospital, the man who spearheaded the creation of its new pediatric neurosurgery unit. But increasingly, his reputation and perpetual motion revolve around his conviction that in the health professions, the kitchen must
