Jean Carper's 20th book, Miracle Cures, is also her fastest-selling book. HarperCollins has gone back to press four times, bringing the in-print total to more than 175,000 copies; the book went on sale July 7. Carper, an authority on health and nutrition, focuses on 21 "miracle cures" that use natural remedies (among the case histories she recounts: a woman in her 50s lowered her cholesterol by 90 points in one month with grapefruit fiber). Her media tour includes interviews on Today, NPR, CBS and CNN (a familiar setting -- Carper was once the network's senior medical correspondent). She is also doing an eight-city tour.