Hi. Thanks for your query. Noted the history about your wife who is 78 years old and understood your concerns. Surely yes, the recommended dose of 3400 max of Aspartame can cause loose stools and Hawaiian Punch Drink too can add on the problems. The sure shot diagnosis can be made by stopping both these and see whether the loose motions stop or not. If stopping these help means your wife has to stop these and find another alternatives so that the loose stools stop. Also watch for any other foods and beverages that can cause intolerance and thus IBS although the most important point in IBS is noral relevant investigations. Hence I would advise her the following considering her age. First of all to get the stool tested for a few days to see if there is any intestinal infection or any other problems and if present get treated accordingly say by an antibiotic, metronidazole and probiotics. If all the investigations are normal then this may be IBS and control of stress would be very important.