18 months post op, RNY, and I drink sugar free soda daily, not that I should, but I do. And I don't have any issues with it. I can gulp water if I have an empty stomach, can't gulp soda, but I can sip it like normal and I love it. I even drink it with a straw. Everyone's experience will be different. I waited at least 6 months before experimenting, and I would recommend going very slow, a sip or two at a time until you know what will happen.