I was told by my surgeon that carbonated beverages can cause bloating which can swell the stomach, cause acid reflux, deteriorate the stomach lining over time, can cause ulcers over time, and gas is certain. I was a Diet Cherry Pepsi-holic so that sucked for me. As far as the caffeine goes the day after my surgery I was given a 6 oz cup of unsweetened tea on my meal tray with a pack of Splenda and a Boost. I tried it out but it tasted like crap. I'm Southern I need my sweet tea so if I can't have it like I want it then I prefer to not have it at all. I've been drinking Vitamin Water Zero and the new Mio's where you squirt it into the drink. They are the two things I tolerate the best and they are no carbon, no caffeine, low sodium, and still taste sweet and good to me. I just prefer not to risk it being how hard this whole process has been on me.