Dr. Atkins is dead and never before has this country been more suspicious of the fad ''diet.'' You can count calories till the cows come home and cry out over every carbohydrate, but NONE of these activities will you take off the pounds and keep your weight at a healthy level for life. In Ultrametabolism, Dr Mark Hyman uses the latest findings from the exploration of genetics to create a new science of weight loss. From the genetic research of the last few years, scientists have learned that food acts as ''messages'' or ''signals'' that activate and instruct the metabolism to function in a fast, healthy manner or a sluggish, sick one. Eat the right ''messages'' and you will maintain a lean, healthy body weight for life. Ultrametabolism includes a six-week programme of detox, rebalancing the metabolism, and stabilizing it for a life of healthy weight loss and maintenance. Menus and recipes created with a nutritionist from the famous Canyon Ranch in the Berkshires offer suggestions for the reader embarking on the plan.