I think for the most part, the diet we follow post-surgery (whether sleeve or bypass) is what is known as protein-prioritized keto (there's a FB group if you are interested). Keep protein high, fats low to moderate, and carbs low. In fact, I really don't understand the (traditional keto) focus on high fat since the reason most people lose weight is because of low carbs. And of course protein is better for you than fat. That said, some people may be more sensitive to fatty foods after bypass (I just had a bypass revision myself and this is something I'm concerned about). I would talk to your doctor/nutritionist to see what they think.