Going On the liquid Diet

Can anyone tell me what was the best liquid diet for losing weight fast?

Is this a pre-op liquid diet?  My surgeon requires his patients 4 weeks of this before surgery.  He recommends Ensure or Glucerna meal replacement drinks.  They're available here in Canada.  I think they actually say on them that they're good preparation for surgery.  I think they're about 300 calories each and include all the necessary vitamins and minerals.  They're milk based.

 My doctor put me on Champion Nutrition Ultramet Original High Protein Meal Replacement shakes for 2 weeks before my surgery which is on 12/27/12. They are thick, taste good, only use water, and are easy to make. I bought a small portable blender so I could make them in my office at work. The thickness makes them pretty filling too.

 I always add a teaspoon of sugar free pudding mix to my shakes to make them thicker. Or a few strawberries.