Part of “Healthy 2010,” a series offering tips on the best ways to experience optimal health and fitness during the year. Forget about Atkins. Ditch South Beach and The Zone. Cut out cabbage and low-carb, faux-carb, no-carb and the rest of the gimmicks many people turn to when it’s time to lose weight. There’s really only one diet plan to follow for safe, long-lasting weight loss, according to a registered dietitian, and it’s based on simple math.