Katahn, the director of Vanderbilt University's Weight Management Program, herewith reveals the secret of this latest miracle pound-paring regimen. For women, it consists simply of a balanced 600-calorie diet for three days, followed by 900 calories the next four days, 1200 for one week and then back to 600 for three days and, finally, 900 for four days. For men, the rotation totals are 1200, 1500 and 1800. Also mandated is at least 45 minutes a day of whole-body exercise such as brisk walking, moderate jogging, swimming, bicycling, etc. At the end of the 21-day period, the dieter takes a week's to a month's break from stringent calorie counting, but not from daily exercise. No weight gain should occur during these breaks, says Katahn, because this diet is structured to prevent a slowdown in the metabolic rate. Calorie rotating should be resumed at fairly regular intervals until the desired weight is reached. Katahn's regimen permits an almost unlimited amount of certain low-calorie vegetables plus a snack of specified fruits. Otherwise, it provides for three strenuously stringent to moderately spartan meals a day, with lunches and dinners primarily based on small amounts of fish, seafood, diet cottage cheese, chicken and lean beef along with whole-grain bread, brown rice, small baked potatoes, etc. He includes a number of recipes that neatly vary the taste of the constantly reappearing basic ingredients. The recommended menus are nutritionally sound and his calorie quotas appear to be safe for most healthy men and women. One wonders, however, whether it makes sense to recommend a higher-calorie regimen for all men than for women, some of whom tower over a number of males.