Thanks a lot!

The details of what's done/required vary from surgeon to surgeon and also depend on insurance requirements. Plus, there are three common types of surgery that are performed and each has its own peculiarities.

In my case (and I had the Roux-en-Y procedure because it is the one that is most effective at treating Type II diabetes) I had to be on a medically supervised diet for at least six months. No requirement that it be LC or any other particular diet, just that it be medically supervised.

Post surgery (for this procedure) you need to avoid certain types of foods as they cause "dumping syndrome" (a fancy term for severe diarrhea) because the duodenum has been bypassed. The biggest culprit is sugar. But fats in any significant quantity are also problems as is alcohol. You are also highly discouraged from drinking carbonated beverages.

Your intake is limited to about 2 oz (volume) per meal, but this increases as the new stomach pouch expands and eventually settles in at about 8 oz. Once the initial liquid/pureed/soft diet phases are over (about six weeks total) you are typically at about 500 Cal/day (say 300 Cal to 800 Cal) with the general guideline that you eat protein first, then veggies, then fruit, then starches in very limited quantities. Most people stay at this level throughout most of their weight loss phase and then increase it to a sustainable level as they near the end of that.