Dr. Jana Klauer's high-profile, hard-charging Manhattan patients can't afford to be off their game. Maybe it's the after-lunch slump, or the inability to focus on a crucial task at deadline time. It could be a constant nagging tiredness, or a thickening waistline, even when they're exercising. Klauer's patients go to Park Avenue's premier nutritionist for results: to look and feel better. And they get them.In "The Park Avenue Nutritionist's Plan,"...