Still weighing in at 128 pounds (after many years over 200), newspaper columnist Barbara Gibbons continues her pursuit of decalorizing good food. ""To hell with Julia and Craig,"" she exclaims, substituting diet margarine for butter and a variety of less caloric ingredients for cream or whole milk--cottage cheese, yogurt, skim milk. Like The Slim Gourmet Cookbook (1976), this features Gibbons' chummy remarks (""Make friends with fish!"") and undemanding kitchen techniques--none of that tricky Troisgrois stuff. And the substitutions are less exotic: turkey thigh for duck (a juicy 92 calories per ounce), chopped olives for olive oil, chicken browned in its own melted (and then discarded) fat. Some, however, are inexplicable: why should rice pudding include canned fruit cocktail and gin--the last heaps on 60 calories per serving. Overall, though, lots of cooks will go for these variations: they're easy, many yield an edible enough meal, and few foods are entirely proscribed.