first of all
Now,

my doctor gave me guidelines such as stay under 100 fat grams...which was a very high and attainable number. I didn't lose much during the 6 month supervised diet but that was not the plan...I just had to show that I could follow a plan and stick to it. My BMI was 44 and my insurance didn't want me under a 40 so maintainance was ideal for me.
My surgeon didn't require any pre-surgery diet as long as I didn't gain much weight. But there are some advantages to letting go of high fat foods such as Fast Food and the like. One being that your liver is larger when trying to process that kind of fat making it harder to do surgery laporscopicly and the smaller you are before hand, the safer the surgery is and easier it is to recover from.
I spent my last 2 months before surgery "saying goodbye" to food. Once I said goodbye to something, I didn't eat it any more. I am very glad that I did that!
Good luck to you on the beginning of a grand (as in large and life changing) journey, iswood!
Angela