There's another diet program out there that touts 20 lbs in 28 days, can't recall the name... something Metabolism, authors first name is Haylie, and she is a veterinarian turned nutritionist and health coach. supposedly she knows about fattening animals up, or in the case of race horses, leaning them out without compromising muscle.
Her basic approach is cycling through 3 phases per week,
Phase 1 - 2 days carbs (650-750 cals),
Phase 2 - 2 days lean protein & non starch veg (800-900 cals), and
Phase 3 - 3 days 50% fat, 50% split between protein & non starch carbs (1100-1300 cals).
No wheat, no dairy, no sugar.
I did not read the book, I read some reviews. The basic menu on phase one looked like oatmeal & fruit, on phase 2 meats and salads, phase 3 is a good mix but even so, still low calorie.