I can't recommend any websites, but I can tell you some personal observations as far as gastric bypass surgery.
I know 2 women who were both morbidly obese, who had gastric bybass. Both these women are nurses.
The percentage of comeplete protein MUST constitute a larger percentage of your diet after such a surgery, in order for you body to function properly.
In other words, since you are restricted in the amount of food you can eat (as in a stomach reduction) or the amount of nutrients absorbed, you have to take advantage of the nutrition in every food you eat.
Person "A" took excellant care of herself, eating much lean meat, not wasting her time on starches, taking supplements, and exercise. When she reached her proper weight, she had surgery to remove excess skin. Which required her to be even more careful with what she put in her body, as far as being able to heal properly..Your body needs protein to heal. Today, she looks years younger than her true age, and has general good health.
Person "B" at first lost a lot of weight, and looked better, as far as losing 100 pounds or more would make anyone look better. However, I was in her company 3 or 4 times to eat in buffet situations, and was surprised by her choices.....taking bread products, other food that were bulky but not particularly nutritious. She actually chose not to eat any protein at one of the meals so that she could have a piece of baklava
During that time she showed me her surgery scar....she'd had the operation a year before.....it was a angry red scar running down her abdomen. I said "Wow! That doesn't look like it's even healed!!!"
Her response was...."yes, it's hard to get enough protein for it to heal." Well, yeah, especially when you're eating pastry. Plus, she refused to exercise.
Last time I saw her, about 2 years after the surgery, she was back to being obese.
That said, I'd say one of the most important side effects of the surgery is the bodies ability to heal itself, depending on what you choose to put into it.