I am not sure what your dietician is telling you, but why not ask your surgeon? Won't it be his guidelines you are/will follow? Or did he refer you to your dietician?
I don't know, but it sounds CRAZY to me. The only pre-op diet I had was a liquid diet the day before surgery. ONE DAY. After surgery, I was on a liquid diet of broth and jello for I think a day and a half...my supper that 2nd day included mashed potatoes and gravy and some pureed chicken noodle soup. So at that point I was on a "soft foods only diet." When I was released from the hospital, day 5 I was eating pasta, jello, mashed potatoes, banannas, watermelon, strawberries...soft foods. I started eating more because I was starving, not because my doctor recommended at like 8 days. I started eating tuna fish and chicken. At my 2 week appointment my doctor said that I could start adding that chicken and fish that I had already started on. I am 3 1/2 weeks out and I can eat ANYTHING. I mean, the taco bell I tried gave me a good case of gas, but I ate it without getting "sick." Of course, I ate very little. My son had his 11th birthday last weekend (I was just 3 weeks out) and we went to the fair. I had a bit of cake, a spoonful of strawberry ice cream at his party, a few bites of corn on the cob, some nacho chips and mexicali dip and I even had a couple sour cream and onion potatoe chips...at the fair...I tried a couple bites of cotton candy, a bite of pizza and even bought myself a baby chocolate ice cream cone (which I had to have my mother keep licking for me as if I were 3) and the majority of it ended up on my shirt because I just couldn't eat it as fast as ice cream cones need to be eaten on warm summer days. I wouldn't recommend to anyone, let alone a DSer to eat like this but it was a special day packed with "fun" food and I was feeling pretty good and decided that a bite or two couldn't hurt. I am sure most would not recommend this either, but I am just trying to tell you that if at 3 weeks out I can eat ANYTHING, I have no idea why you would need to be on a liquid diet for 2 weeks after. I know that some doctors recommend a soft food diet for quite a while, but liquids seems extreme to me.
The ONLY thing I have not tried is salads...but I plan on doing that as soon as I am able to eat a bit more at one time.
I also probably eat a bit differently than most. I do not eat meals. I eat a few to several bites or a handful or dixie cup full of something every couple of hours throughout the day.
I would double check. Four weeks of liquid diet seems like undue torture to me.
Best of luck!