Anxious,Interesting question about soft drinks,I work for one of the "big 2"soda companies and I have some answers that are liable to cause more questions. The syrup used to make prepacked and fountain are identical,there are,however,some differences in the finished product.Prepackaged and PREmix fountain(the kind of fountain you'll find in smaller restuarants,portables at sporting events etc) are made with water that has been highly purified at the point of production.POSTmix(Found in large volume distribution points,fastfood,plant cafeterias,sports arenas etc)is mixed with local water.There may be some food for thought there,I know water I'm not used to can be a trigger for me.Also,both "mixes"tend to be dispensed at a higher carbonation rate than prepacked,so that may be a problem also.Interestingly,I'm aware of a fellow IBSer who can apparently drink pepsi with no problem,but gets set off by coke.Go figure. Rosie,I'm curious to know how your experiment works.I'm a 4-5 cup a day coffee drinker,stopping doesn't help,starting up again doesn't make things worse.I seem to be able to handle the "stealth"caffiene sodas(most of the citrus based flavors have more than anything)but have to take it very easy on colas,regular or caff-free doesn't seem to matter.