There is no dumping in IBS from D. The stomach absorbs the nutrients and in IBS the sigmoid colon is basically the problem. IBSers do not digest food differently then normal people. There is no malabsorbtion of nutrients due to the d.
"There is no evidence that digestion of food is different in those with IBS compared to those without IBS. Diet, food and eating do not cause IBS. However, muscles and nerves are over-reactive in IBS. This can cause the bowel to over-respond to stimuli. Even a normal event such as the act of eating itself, and not a particular food, may aggravate symptoms at times. Eating releases hormones that stimulate the gut."