How can you do it?
Well for a start forget about worrying over the pre op diet. Its two weeks and you are at least 102 weeks away from it. In the same way you are 104 weeks away from the post op diet and to be honest unless you are stupid the post op diet kind of takes care of itself at first
As for the period between then and now! well don't they say 90% of diets fail? I believe WW is more about lifestyle than diet these days
and that's a good thing of it's true. Our brains are not wired for starvation diets or diets based on denial to work. The more we deny ourselves something the more our heads find reasons for us to have it. Thats why WLS is so much easier as a means to losing weight because it helps us break that yo yo denial/binge eating cycle. WLS gives us something that can help reduce the cravings if we do our bit and follow the rules.
I didn't diet pre op, but I was told that at 400 pounds I had an increased risk of surgical complications and the more weight I lost pre op the better chance of survival I would have. So I just cut down what I ate and when and how much. Nothing spectacular or severe I just made slghtly better choices. I lost 55 lbs during that time without really noticing it.
Just make small changes, park the car three rows down at the supermarket instead of waiting until the space near the door is free, take the stairs now again instead of the lift or escalator. Make protein foods your friends and even when you have to snack have a protein based snack such as dry roasted peanuts etc. Get in some chocolate covered protein bars or meal replacements instead of KitKats etc, not only are they much better for you, they cost so much one every two days is all you'll want to buy
Finally, take it one day at a time, but start to make these small changes
now. Don't do what most of us did and focus just on the surgery date and trick yourself into thinking that surgery will make it all OK.
It won't not on it's own it won't.
Forget you're on a diet, short term or fad diets don't work, its lifestyle that counts. Eat a little less, eat a little better, and move a little more. Do this and you'll be fine. Good luck x