Immediately after GB removal, you need to eat lightly and blandly. D right afterwards is fairly common and there's not a whole lot you can do to stop it except take preemptive imodiums, but there are some things that make it worse. White starches are your friend right now. I found right after my surgery that red meat and pork bothered me, but chicken was okay, so that was my meat of choice (lean fish, like tuna, should also be okay). Pork and beef are both higher in fat and harder to digest. Even with the chicken (or turkey), you need to stick to white meat only. Dark is too fatty. Stay away from fats and caffeine and hot spices (e.g. Mexican food) and acidic things, inluding fruit, fruit juices and tomatoes. White bread, pasta, white rice and potatoes are all good sides. Also stay away from dairy products.
Mind you, this bland, monotonous diet only needs to go one for 4-6 weeks, then you should be more or less stabilized, to whatever your body will tolerate or not tolerate, and then you can start adding things back in. While I'm still mostly a chicken person (was before anyways), I can tolerate red meat and pork fine. I also can do dairy products and veggies. Fruit juices and most all raw fruits are out, although tomatoes are okay in moderation and provided I don't already have the start of heartburn. Caffeine is still evil. I can only, on rare occasion, have fast food and tolerate it. Bad fats, such as partially-hydrogenated junk, are still bad on my guts. Sugar alcohols, from sugar-free candies, are so terrible on me I tell people I'm allergic to them. Nothing is worse than 1 gram of sugar alcohol except 2 grams of sugar alcohol.
What you will and won't be able to eat will depend entirely on your body alone. Some people are capable of eating anything they want after this adjustment period is over with, while some people are like me and have limitations.