@KetoRestartAnn you absolutely can do keto with a gastric bypass and no gallbladder! You must just learn and get to know your body. You still can digest fat, you just must pace it carefully at first to acclimate. I would not eat primarily fat at first. Gradually add more and see how it goes. Fasting may be tricky. Of course, we are still more efficient post-op than people dieting after fat adaptation. Our altered anatomy does give us an edge, however slight. Still, I also know many RNY patients that do intermittent fasting, if not monthly extended fasts, too. Just go very slowly and don't rush. You will probably feel 100x better, too, actually.
Many RNY/bypass patients do keto post-op, and many DS patients do keto post-op. They may call it "low carb" or "very low carb," however they are basically eating a ketogenic diet, too.
There is an enormous community of bariatric patients who do low carb/keto. It's unfortunate that most of the low carb/keto celebrities ignore us, because we are a huge demographic. There are over 200,000 surgeries a year alone in the US. Just think of what good it would accomplish to target this audience both pre and post-op.