While many American kids grow up eating peanut butter, in recent years, a wide variety of different kinds of nut and seed butters have hit the grocery store shelves. But what kind of nutritional value to they all provide? This week on “Take Care,” sports nutritionist Nancy Clark gives us a primer on nut and seed butters. Clark is the author of “Nancy Clark's Sports Nutrition Guidebook.” She writes the monthly nutrition column “The Athlete's Kitchen,” which appears in over 100 sports and fitness