I know plenty of people that allow their fizzy drink to go flat, then drink it...it's a fallacy that the heat in the stomach 're-activates' a carbonated drink...a drink it carbonated by dissolving CO2 into the fluid under high pressure, once the pressure is reduced, the CO2 begins to dissipate out of the fluid (seen as small bubbles), once to CO2 is out, it's out for good! One would literally have to go back through the process of re-carbonating the drink for it to become fizzy again. The main reason why WLS patients are advised not to drink carbonated drinks is because the build up of CO2 in the pouch can cause it to stretch.